diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c index b1c4ceb..aef0fcc 100644 --- a/drivers/base/devtmpfs.c +++ b/drivers/base/devtmpfs.c @@ -413,7 +413,7 @@ static noinline int __init devtmpfs_setup(void *p) { int err; - err = ksys_unshare(CLONE_NEWNS); + err = ksys_unshare(UNSHARE_EMPTY_MNTNS); if (err) goto out; err = init_mount("devtmpfs", "/", "devtmpfs", DEVTMPFS_MFLAGS, NULL); diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c index 10e8c43..79c9a5f 100644 --- a/drivers/block/rnbd/rnbd-srv.c +++ b/drivers/block/rnbd/rnbd-srv.c @@ -11,6 +11,7 @@ #include #include +#include #include "rnbd-srv.h" #include "rnbd-srv-trace.h" @@ -734,7 +735,8 @@ static int process_msg_open(struct rnbd_srv_session *srv_sess, goto reject; } - bdev_file = bdev_file_open_by_path(full_path, open_flags, NULL, NULL); + scoped_with_init_fs() + bdev_file = bdev_file_open_by_path(full_path, open_flags, NULL, NULL); if (IS_ERR(bdev_file)) { ret = PTR_ERR(bdev_file); pr_err("Opening device '%s' on session %s failed, failed to open the block device, err: %pe\n", diff --git a/drivers/char/misc_minor_kunit.c b/drivers/char/misc_minor_kunit.c index e930c78..e85210c 100644 --- a/drivers/char/misc_minor_kunit.c +++ b/drivers/char/misc_minor_kunit.c @@ -5,6 +5,7 @@ #include #include #include +#include #include /* static minor (LCD_MINOR) */ @@ -160,18 +161,22 @@ static void __init miscdev_test_can_open(struct kunit *test, struct miscdevice * char *devname; devname = kasprintf(GFP_KERNEL, "/dev/%s", misc->name); - ret = init_mknod(devname, S_IFCHR | 0600, - new_encode_dev(MKDEV(MISC_MAJOR, misc->minor))); - if (ret != 0) - KUNIT_FAIL(test, "failed to create node\n"); - filp = filp_open(devname, O_RDONLY, 0); - if (IS_ERR(filp)) - KUNIT_FAIL(test, "failed to open misc device: %ld\n", PTR_ERR(filp)); - else - fput(filp); + /* Tests run in a nullfs kthread; borrow the init fs to resolve /dev. */ + scoped_with_init_fs() { + ret = init_mknod(devname, S_IFCHR | 0600, + new_encode_dev(MKDEV(MISC_MAJOR, misc->minor))); + if (ret != 0) + KUNIT_FAIL(test, "failed to create node\n"); + + filp = filp_open(devname, O_RDONLY, 0); + if (IS_ERR(filp)) + KUNIT_FAIL(test, "failed to open misc device: %ld\n", PTR_ERR(filp)); + else + fput(filp); - init_unlink(devname); + init_unlink(devname); + } kfree(devname); } diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c index ca473ca..0f72352 100644 --- a/drivers/crypto/ccp/sev-dev.c +++ b/drivers/crypto/ccp/sev-dev.c @@ -260,20 +260,16 @@ static int sev_cmd_buffer_len(int cmd) static struct file *open_file_as_root(const char *filename, int flags, umode_t mode) { - struct path root __free(path_put) = {}; - - task_lock(&init_task); - get_fs_root(init_task.fs, &root); - task_unlock(&init_task); - CLASS(prepare_creds, cred)(); if (!cred) return ERR_PTR(-ENOMEM); cred->fsuid = GLOBAL_ROOT_UID; - scoped_with_creds(cred) - return file_open_root(&root, filename, flags, mode); + scoped_with_init_fs() { + scoped_with_creds(cred) + return filp_open(filename, flags, mode); + } } static int sev_read_init_ex_file(void) diff --git a/drivers/target/target_core_alua.c b/drivers/target/target_core_alua.c index 10250ac..140154d 100644 --- a/drivers/target/target_core_alua.c +++ b/drivers/target/target_core_alua.c @@ -18,6 +18,8 @@ #include #include #include +#include +#include #include #include @@ -856,10 +858,17 @@ static int core_alua_write_tpg_metadata( unsigned char *md_buf, u32 md_buf_len) { - struct file *file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600); + struct file *file; loff_t pos = 0; int ret; + if (tsk_is_kthread(current)) { + scoped_with_init_fs() + file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600); + } else { + file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600); + } + if (IS_ERR(file)) { pr_err("filp_open(%s) for ALUA metadata failed\n", path); return -ENODEV; diff --git a/drivers/target/target_core_pr.c b/drivers/target/target_core_pr.c index 1a77b4b..25b1bca 100644 --- a/drivers/target/target_core_pr.c +++ b/drivers/target/target_core_pr.c @@ -18,6 +18,7 @@ #include #include #include +#include #include #include @@ -1969,7 +1970,8 @@ static int __core_scsi3_write_aptpl_to_file( if (!path) return -ENOMEM; - file = filp_open(path, flags, 0600); + scoped_with_init_fs() + file = filp_open(path, flags, 0600); if (IS_ERR(file)) { pr_err("filp_open(%s) for APTPL metadata" " failed\n", path); diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 6eab4cc..dc5f4a1 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -12,6 +12,7 @@ #include #include #include +#include #include "misc.h" #include "disk-io.h" #include "extent-tree.h" @@ -2125,8 +2126,16 @@ static int btrfs_add_dev_item(struct btrfs_trans_handle *trans, static void update_dev_time(const char *device_path) { struct path path; + int err; - if (!kern_path(device_path, LOOKUP_FOLLOW, &path)) { + if (tsk_is_kthread(current)) { + scoped_with_init_fs() + err = kern_path(device_path, LOOKUP_FOLLOW, &path); + } else { + err = kern_path(device_path, LOOKUP_FOLLOW, &path); + } + + if (!err) { vfs_utimes(&path, NULL); path_put(&path); } diff --git a/fs/coredump.c b/fs/coredump.c index e68a76f..ac3cd74 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -921,15 +921,10 @@ static bool coredump_file(struct core_name *cn, struct coredump_params *cprm, * with a fully qualified path" rule is to control where * coredumps may be placed using root privileges, * current->fs->root must not be used. Instead, use the - * root directory of init_task. + * root directory of PID 1. */ - struct path root; - - task_lock(&init_task); - get_fs_root(init_task.fs, &root); - task_unlock(&init_task); - file = file_open_root(&root, cn->corename, open_flags, 0600); - path_put(&root); + scoped_with_init_fs() + file = filp_open(cn->corename, open_flags, 0600); } else { file = filp_open(cn->corename, open_flags, 0600); } diff --git a/fs/fs_struct.c b/fs/fs_struct.c index 394875d..34699f3 100644 --- a/fs/fs_struct.c +++ b/fs/fs_struct.c @@ -8,6 +8,7 @@ #include #include #include "internal.h" +#include "mount.h" /* * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values. @@ -60,8 +61,11 @@ void chroot_fs_refs(const struct path *old_root, const struct path *new_root) read_lock(&tasklist_lock); for_each_process_thread(g, p) { + if (p->flags & (PF_KTHREAD | PF_EXITING | PF_DUMPCORE)) + continue; + task_lock(p); - fs = p->fs; + fs = p->real_fs; if (fs) { int hits = 0; write_seqlock(&fs->seq); @@ -89,12 +93,13 @@ void free_fs_struct(struct fs_struct *fs) void exit_fs(struct task_struct *tsk) { - struct fs_struct *fs = tsk->fs; + struct fs_struct *fs = tsk->real_fs; if (fs) { int kill; task_lock(tsk); read_seqlock_excl(&fs->seq); + tsk->real_fs = NULL; tsk->fs = NULL; kill = !--fs->users; read_sequnlock_excl(&fs->seq); @@ -126,7 +131,7 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old) int unshare_fs_struct(void) { - struct fs_struct *fs = current->fs; + struct fs_struct *fs = current->real_fs; struct fs_struct *new_fs = copy_fs_struct(fs); int kill; @@ -135,8 +140,10 @@ int unshare_fs_struct(void) task_lock(current); read_seqlock_excl(&fs->seq); + VFS_WARN_ON_ONCE(fs != current->fs); kill = !--fs->users; current->fs = new_fs; + current->real_fs = new_fs; read_sequnlock_excl(&fs->seq); task_unlock(current); @@ -147,9 +154,99 @@ int unshare_fs_struct(void) } EXPORT_SYMBOL_GPL(unshare_fs_struct); +/* + * PID 1 may choose to stop sharing fs_struct state with us. + * Either via unshare(CLONE_FS) or unshare(CLONE_NEWNS). Of + * course, PID 1 could have chosen to create arbitrary process + * trees that all share fs_struct state via CLONE_FS. This is a + * strong statement: We only care about PID 1 aka the thread-group + * leader so subthread's fs_struct state doesn't matter. + * + * PID 1 unsharing fs_struct state is a bug. PID 1 relies on + * various kthreads to be able to perform work based on its + * fs_struct state. Breaking that contract sucks for both sides. + * So just don't bother with extra work for this. No sane init + * system should ever do this. + * + * On older kernels if PID 1 unshared its filesystem state with us the + * kernel simply used the stale fs_struct state implicitly pinning + * anything that PID 1 had last used. Even if PID 1 might've moved on to + * some completely different fs_struct state and might've even unmounted + * the old root. + * + * This has hilarious consequences: Think continuing to dump coredump + * state into an implicitly pinned directory somewhere. Calling random + * binaries in the old rootfs via usermodehelpers. + * + * Be aggressive about this: We simply reject operating on stale + * fs_struct state by reverting to nullfs. Every kworker that does + * lookups after this point will fail. Every usermodehelper call will + * fail. Tough luck but let's be kind and emit a warning to userspace. + */ +static inline void validate_fs_switch(struct fs_struct *old_fs) +{ + might_sleep(); + + if (likely(current->pid != 1)) + return; + /* @old_fs may be dangling but for comparison it's fine */ + if (old_fs != userspace_init_fs) + return; + pr_warn("VFS: Pid 1 stopped sharing filesystem state\n"); + set_fs_root(userspace_init_fs, &init_fs.root); + set_fs_pwd(userspace_init_fs, &init_fs.root); +} + +struct fs_struct *switch_fs_struct(struct fs_struct *new_fs) +{ + struct fs_struct *fs; + + scoped_guard(task_lock, current) { + fs = current->fs; + VFS_WARN_ON_ONCE(fs != current->real_fs); + read_seqlock_excl(&fs->seq); + current->fs = new_fs; + current->real_fs = new_fs; + if (--fs->users) + new_fs = NULL; + else + new_fs = fs; + read_sequnlock_excl(&fs->seq); + } + + validate_fs_switch(fs); + return new_fs; +} + /* to be mentioned only in INIT_TASK */ struct fs_struct init_fs = { .users = 1, .seq = __SEQLOCK_UNLOCKED(init_fs.seq), .umask = 0022, }; + +struct fs_struct *userspace_init_fs __ro_after_init; +EXPORT_SYMBOL_GPL(userspace_init_fs); + +void __init init_userspace_fs(void) +{ + struct mount *m; + struct path root; + + /* Move PID 1 from nullfs into the initramfs. */ + m = topmost_overmount(current->nsproxy->mnt_ns->root); + root.mnt = &m->mnt; + root.dentry = root.mnt->mnt_root; + + VFS_WARN_ON_ONCE(current->pid != 1); + + set_fs_root(current->fs, &root); + set_fs_pwd(current->fs, &root); + + /* Hold a reference for the global pointer. */ + read_seqlock_excl(¤t->fs->seq); + current->fs->users++; + read_sequnlock_excl(¤t->fs->seq); + + userspace_init_fs = current->fs; +} diff --git a/fs/kernel_read_file.c b/fs/kernel_read_file.c index de32c95..9c2ba92 100644 --- a/fs/kernel_read_file.c +++ b/fs/kernel_read_file.c @@ -150,18 +150,13 @@ ssize_t kernel_read_file_from_path_initns(const char *path, loff_t offset, enum kernel_read_file_id id) { struct file *file; - struct path root; ssize_t ret; if (!path || !*path) return -EINVAL; - task_lock(&init_task); - get_fs_root(init_task.fs, &root); - task_unlock(&init_task); - - file = file_open_root(&root, path, O_RDONLY, 0); - path_put(&root); + scoped_with_init_fs() + file = filp_open(path, O_RDONLY, 0); if (IS_ERR(file)) return PTR_ERR(file); diff --git a/fs/namespace.c b/fs/namespace.c index 87c365f..eca22ce 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -6184,12 +6184,14 @@ static void __init init_mount_tree(void) struct path root; /* - * We create two mounts: + * We create three mounts: * * (1) nullfs with mount id 1 * (2) mutable rootfs with mount id 2 + * (3) private nullfs for kthreads (SB_KERNMOUNT) * - * with (2) mounted on top of (1). + * with (2) mounted on top of (1). The init_task's root and pwd + * are pointed at (3) so all kthreads start isolated in nullfs. */ nullfs_mnt = vfs_kern_mount(&nullfs_fs_type, 0, "nullfs", NULL); if (IS_ERR(nullfs_mnt)) @@ -6229,12 +6231,14 @@ static void __init init_mount_tree(void) init_mnt_ns.nr_mounts++; } + nullfs_mnt = kern_mount(&nullfs_fs_type); + if (IS_ERR(nullfs_mnt)) + panic("VFS: Failed to create private nullfs instance"); + root.mnt = nullfs_mnt; + root.dentry = nullfs_mnt->mnt_root; + init_task.nsproxy->mnt_ns = &init_mnt_ns; get_mnt_ns(&init_mnt_ns); - - /* The root and pwd always point to the mutable rootfs. */ - root.mnt = mnt; - root.dentry = mnt->mnt_root; set_fs_pwd(current->fs, &root); set_fs_root(current->fs, &root); diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c index bb35f88..368d20d 100644 --- a/fs/nfs/blocklayout/dev.c +++ b/fs/nfs/blocklayout/dev.c @@ -4,6 +4,7 @@ */ #include #include +#include #include #include #include @@ -363,15 +364,22 @@ static struct file * bl_open_path(struct pnfs_block_volume *v, const char *prefix) { struct file *bdev_file; - const char *devname; + const char *devname __free(kfree) = NULL; devname = kasprintf(GFP_KERNEL, "/dev/disk/by-id/%s%*phN", prefix, v->scsi.designator_len, v->scsi.designator); if (!devname) return ERR_PTR(-ENOMEM); - bdev_file = bdev_file_open_by_path(devname, - BLK_OPEN_READ | BLK_OPEN_WRITE, NULL, NULL); + if (tsk_is_kthread(current)) { + scoped_with_init_fs() + bdev_file = bdev_file_open_by_path(devname, + BLK_OPEN_READ | BLK_OPEN_WRITE, + NULL, NULL); + } else { + bdev_file = bdev_file_open_by_path(devname, + BLK_OPEN_READ | BLK_OPEN_WRITE, NULL, NULL); + } if (IS_ERR(bdev_file)) { dprintk("failed to open device %s (%ld)\n", devname, PTR_ERR(bdev_file)); @@ -380,7 +388,6 @@ bl_open_path(struct pnfs_block_volume *v, const char *prefix) file_bdev(bdev_file)->bd_disk->disk_name); } - kfree(devname); return bdev_file; } diff --git a/fs/nullfs.c b/fs/nullfs.c index fdbd3e5..c6f5b94 100644 --- a/fs/nullfs.c +++ b/fs/nullfs.c @@ -40,14 +40,9 @@ static int nullfs_fs_fill_super(struct super_block *s, struct fs_context *fc) return 0; } -/* - * For now this is a single global instance. If needed we can make it - * mountable by userspace at which point we will need to make it - * multi-instance. - */ static int nullfs_fs_get_tree(struct fs_context *fc) { - return get_tree_single(fc, nullfs_fs_fill_super); + return get_tree_nodev(fc, nullfs_fs_fill_super); } static const struct fs_context_operations nullfs_fs_context_ops = { @@ -57,9 +52,8 @@ static const struct fs_context_operations nullfs_fs_context_ops = { static int nullfs_init_fs_context(struct fs_context *fc) { fc->ops = &nullfs_fs_context_ops; - fc->global = true; - fc->sb_flags = SB_NOUSER; - fc->s_iflags = SB_I_NOEXEC | SB_I_NODEV; + fc->sb_flags |= SB_NOUSER; + fc->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; return 0; } diff --git a/fs/proc/array.c b/fs/proc/array.c index 479ea8c..f6f75d2 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -168,8 +168,8 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, cred = get_task_cred(p); task_lock(p); - if (p->fs) - umask = p->fs->umask; + if (p->real_fs) + umask = p->real_fs->umask; if (p->files) max_fds = files_fdtable(p->files)->max_fds; task_unlock(p); diff --git a/fs/proc/base.c b/fs/proc/base.c index 780f812..6a39de4 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -211,8 +211,8 @@ static int get_task_root(struct task_struct *task, struct path *root) int result = -ENOENT; task_lock(task); - if (task->fs) { - get_fs_root(task->fs, root); + if (task->real_fs) { + get_fs_root(task->real_fs, root); result = 0; } task_unlock(task); @@ -225,8 +225,8 @@ static int proc_cwd_link(struct dentry *dentry, struct path *path, int result = -ENOENT; task_lock(task); - if (task->fs) { - get_fs_pwd(task->fs, path); + if (task->real_fs) { + get_fs_pwd(task->real_fs, path); result = 0; } task_unlock(task); diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c index 5c555db..036356c 100644 --- a/fs/proc_namespace.c +++ b/fs/proc_namespace.c @@ -254,13 +254,13 @@ static int mounts_open_common(struct inode *inode, struct file *file, } ns = nsp->mnt_ns; get_mnt_ns(ns); - if (!task->fs) { + if (!task->real_fs) { task_unlock(task); put_task_struct(task); ret = -ENOENT; goto err_put_ns; } - get_fs_root(task->fs, &root); + get_fs_root(task->real_fs, &root); task_unlock(task); put_task_struct(task); diff --git a/fs/smb/server/mgmt/share_config.c b/fs/smb/server/mgmt/share_config.c index 6f97f8d..e00aee1 100644 --- a/fs/smb/server/mgmt/share_config.c +++ b/fs/smb/server/mgmt/share_config.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include @@ -193,7 +194,8 @@ static struct ksmbd_share_config *share_config_request(struct ksmbd_work *work, goto out; } - ret = kern_path(share->path, 0, &share->vfs_path); + scoped_with_init_fs() + ret = kern_path(share->path, 0, &share->vfs_path); ksmbd_revert_fsids(work); if (ret) { ksmbd_debug(SMB, "failed to access '%s'\n", diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 76f63f9..d092709 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -5949,7 +5950,8 @@ static int smb2_get_info_filesystem(struct ksmbd_work *work, if (!share->path) return -EIO; - rc = kern_path(share->path, LOOKUP_NO_SYMLINKS, &path); + scoped_with_init_fs() + rc = kern_path(share->path, LOOKUP_NO_SYMLINKS, &path); if (rc) { pr_err("cannot create vfs path\n"); return -EIO; diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c index d324585..e493725 100644 --- a/fs/smb/server/vfs.c +++ b/fs/smb/server/vfs.c @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -67,8 +68,9 @@ static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf, } CLASS(filename_kernel, filename)(pathname); - err = vfs_path_parent_lookup(filename, flags, path, &last, - root_share_path); + scoped_with_init_fs() + err = vfs_path_parent_lookup(filename, flags, path, &last, + root_share_path); if (err) return err; @@ -623,7 +625,8 @@ int ksmbd_vfs_link(struct ksmbd_work *work, const char *oldname, if (ksmbd_override_fsids(work)) return -ENOMEM; - err = kern_path(oldname, LOOKUP_NO_SYMLINKS, &oldpath); + scoped_with_init_fs() + err = kern_path(oldname, LOOKUP_NO_SYMLINKS, &oldpath); if (err) { pr_err("cannot get linux path for %s, err = %d\n", oldname, err); diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h index 0070764..97eef8d 100644 --- a/include/linux/fs_struct.h +++ b/include/linux/fs_struct.h @@ -6,6 +6,7 @@ #include #include #include +#include struct fs_struct { int users; @@ -16,6 +17,7 @@ struct fs_struct { } __randomize_layout; extern struct kmem_cache *fs_cachep; +extern struct fs_struct *userspace_init_fs; extern void exit_fs(struct task_struct *); extern void set_fs_root(struct fs_struct *, const struct path *); @@ -40,6 +42,8 @@ static inline void get_fs_pwd(struct fs_struct *fs, struct path *pwd) read_sequnlock_excl(&fs->seq); } +struct fs_struct *switch_fs_struct(struct fs_struct *new_fs); + extern bool current_chrooted(void); static inline int current_umask(void) @@ -47,4 +51,34 @@ static inline int current_umask(void) return current->fs->umask; } +/* + * Temporarily use userspace_init_fs for path resolution in kthreads. + * Callers should use scoped_with_init_fs() which automatically + * restores the original fs_struct at scope exit. + */ +static inline struct fs_struct *__override_init_fs(void) +{ + struct fs_struct *old_fs; + + old_fs = current->fs; + WRITE_ONCE(current->fs, userspace_init_fs); + return old_fs; +} + +static inline void __revert_init_fs(struct fs_struct *old_fs) +{ + VFS_WARN_ON_ONCE(current->fs != userspace_init_fs); + WRITE_ONCE(current->fs, old_fs); +} + +DEFINE_CLASS(__override_init_fs, + struct fs_struct *, + __revert_init_fs(_T), + __override_init_fs(), void) + +#define scoped_with_init_fs() \ + scoped_class(__override_init_fs, __UNIQUE_ID(label)) + +void __init init_userspace_fs(void); + #endif /* _LINUX_FS_STRUCT_H */ diff --git a/include/linux/init_task.h b/include/linux/init_task.h index a6cb241..61536be 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -24,6 +24,7 @@ extern struct files_struct init_files; extern struct fs_struct init_fs; +extern struct fs_struct *userspace_init_fs; extern struct nsproxy init_nsproxy; #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE diff --git a/include/linux/sched.h b/include/linux/sched.h index 373bcc0..1e4136c 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1191,6 +1191,7 @@ struct task_struct { unsigned long last_switch_time; #endif /* Filesystem information: */ + struct fs_struct *real_fs; struct fs_struct *fs; /* Open file information: */ diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index 41ed884..e0c1ca8 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -31,6 +31,7 @@ struct kernel_clone_args { u32 io_thread:1; u32 user_worker:1; u32 no_files:1; + u32 umh:1; unsigned long stack; unsigned long stack_size; unsigned long tls; diff --git a/init/init_task.c b/init/init_task.c index b67ef60..ba5c252 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -162,6 +162,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = { RCU_POINTER_INITIALIZER(cred, &init_cred), .comm = INIT_TASK_COMM, .thread = INIT_THREAD, + .real_fs = &init_fs, .fs = &init_fs, .files = &init_files, #ifdef CONFIG_IO_URING diff --git a/init/initramfs.c b/init/initramfs.c index 20a18fc..4e27b97 100644 --- a/init/initramfs.c +++ b/init/initramfs.c @@ -6,6 +6,7 @@ #include #include #include +#include #include #include #include @@ -716,7 +717,7 @@ static void __init populate_initrd_image(char *err) } #endif /* CONFIG_BLK_DEV_RAM */ -static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) +static void __init unpack_initramfs(async_cookie_t cookie) { /* Load the built in initramfs */ char *err = unpack_to_rootfs(__initramfs_start, __initramfs_size); @@ -724,7 +725,7 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) panic_show_mem("%s", err); /* Failed to decompress INTERNAL initramfs */ if (!initrd_start || IS_ENABLED(CONFIG_INITRAMFS_FORCE)) - goto done; + return; if (IS_ENABLED(CONFIG_BLK_DEV_RAM)) printk(KERN_INFO "Trying to unpack rootfs image as initramfs...\n"); @@ -739,9 +740,14 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err); #endif } +} -done: - security_initramfs_populated(); +static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) +{ + scoped_with_init_fs() { + unpack_initramfs(cookie); + security_initramfs_populated(); + } /* * If the initrd region is overlapped with crashkernel reserved region, diff --git a/init/initramfs_test.c b/init/initramfs_test.c index bc55306..9cf316c 100644 --- a/init/initramfs_test.c +++ b/init/initramfs_test.c @@ -3,6 +3,7 @@ #include #include #include +#include #include #include #include @@ -562,7 +563,7 @@ static struct kunit_case __refdata initramfs_test_cases[] = { {}, }; -static int __init initramfs_test_init(struct kunit_suite *suite) +static int __init initramfs_suite_init(struct kunit_suite *suite) { /* * unpack_to_rootfs() uses module-static state (victim, byte_count, @@ -574,9 +575,23 @@ static int __init initramfs_test_init(struct kunit_suite *suite) return 0; } +/* Tests run in a nullfs kthread; always use the init fs for path resolution. */ +static int __init initramfs_test_init(struct kunit *test) +{ + test->priv = __override_init_fs(); + return 0; +} + +static void __init initramfs_test_exit(struct kunit *test) +{ + __revert_init_fs(test->priv); +} + static struct kunit_suite __refdata initramfs_test_suite = { .name = "initramfs", - .suite_init = initramfs_test_init, + .suite_init = initramfs_suite_init, + .init = initramfs_test_init, + .exit = initramfs_test_exit, .test_cases = initramfs_test_cases, }; kunit_test_init_section_suites(&initramfs_test_suite); diff --git a/init/main.c b/init/main.c index e363232..92d34e4 100644 --- a/init/main.c +++ b/init/main.c @@ -103,6 +103,7 @@ #include #include #include +#include #include #include #include @@ -670,6 +671,11 @@ static __initdata DECLARE_COMPLETION(kthreadd_done); static noinline void __ref __noreturn rest_init(void) { + struct kernel_clone_args init_args = { + .flags = (CLONE_VM | CLONE_UNTRACED), + .fn = kernel_init, + .fn_arg = NULL, + }; struct task_struct *tsk; int pid; @@ -679,7 +685,7 @@ static noinline void __ref __noreturn rest_init(void) * the init task will end up wanting to create kthreads, which, if * we schedule it before we create kthreadd, will OOPS. */ - pid = user_mode_thread(kernel_init, NULL, CLONE_FS); + pid = kernel_clone(&init_args); /* * Pin init on the boot CPU. Task migration is not properly working * until sched_init_smp() has been run. It will set the allowed @@ -1540,6 +1546,8 @@ static int __ref kernel_init(void *unused) { int ret; + init_userspace_fs(); + /* * Wait until kthreadd is all set-up. */ diff --git a/kernel/fork.c b/kernel/fork.c index f0e2e13..94e021e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1618,9 +1618,27 @@ static int copy_exec_state(u64 clone_flags, struct task_struct *tsk) return task_exec_state_copy(tsk); } -static int copy_fs(u64 clone_flags, struct task_struct *tsk) +static int copy_fs(u64 clone_flags, struct task_struct *tsk, bool umh) { - struct fs_struct *fs = current->fs; + struct fs_struct *fs; + + /* + * Usermodehelper may copy userspace_init_fs filesystem state but + * they don't get to create mount namespaces, share the + * filesystem state, or be started from a non-initial mount + * namespace. + */ + if (umh) { + if (clone_flags & (CLONE_NEWNS | CLONE_FS)) + return -EINVAL; + if (current->nsproxy->mnt_ns != &init_mnt_ns) + return -EINVAL; + fs = userspace_init_fs; + } else { + fs = current->fs; + VFS_WARN_ON_ONCE(current->fs != current->real_fs); + } + if (clone_flags & CLONE_FS) { /* tsk->fs is already what we want */ read_seqlock_excl(&fs->seq); @@ -1633,7 +1651,7 @@ static int copy_fs(u64 clone_flags, struct task_struct *tsk) read_sequnlock_excl(&fs->seq); return 0; } - tsk->fs = copy_fs_struct(fs); + tsk->real_fs = tsk->fs = copy_fs_struct(fs); if (!tsk->fs) return -ENOMEM; return 0; @@ -2277,7 +2295,7 @@ __latent_entropy struct task_struct *copy_process( retval = copy_files(clone_flags, p, args->no_files); if (retval) goto bad_fork_cleanup_semundo; - retval = copy_fs(clone_flags, p); + retval = copy_fs(clone_flags, p, args->umh); if (retval) goto bad_fork_cleanup_files; retval = copy_sighand(clone_flags, p); @@ -2819,6 +2837,7 @@ pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags) .exit_signal = (flags & CSIGNAL), .fn = fn, .fn_arg = arg, + .umh = 1, }; return kernel_clone(&args); @@ -3216,7 +3235,7 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp */ int ksys_unshare(unsigned long unshare_flags) { - struct fs_struct *fs, *new_fs = NULL; + struct fs_struct *new_fs = NULL; struct files_struct *new_fd = NULL; struct cred *new_cred = NULL; struct nsproxy *new_nsproxy = NULL; @@ -3247,6 +3266,10 @@ int ksys_unshare(unsigned long unshare_flags) if (unshare_flags & CLONE_NEWNS) unshare_flags |= CLONE_FS; + /* No unsharing with overriden fs state */ + VFS_WARN_ON_ONCE(unshare_flags & (CLONE_NEWNS | CLONE_FS) && + current->fs != current->real_fs); + err = check_unshare_flags(unshare_flags); if (err) goto bad_unshare_out; @@ -3294,23 +3317,13 @@ int ksys_unshare(unsigned long unshare_flags) new_nsproxy = NULL; } - task_lock(current); + if (new_fs) + new_fs = switch_fs_struct(new_fs); - if (new_fs) { - fs = current->fs; - read_seqlock_excl(&fs->seq); - current->fs = new_fs; - if (--fs->users) - new_fs = NULL; - else - new_fs = fs; - read_sequnlock_excl(&fs->seq); - } - - if (new_fd) + if (new_fd) { + guard(task_lock)(current); swap(current->files, new_fd); - - task_unlock(current); + } if (new_cred) { /* Install the new user namespace */ diff --git a/kernel/kcmp.c b/kernel/kcmp.c index 7c1a65b..76476ae 100644 --- a/kernel/kcmp.c +++ b/kernel/kcmp.c @@ -186,7 +186,7 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES); break; case KCMP_FS: - ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS); + ret = kcmp_ptr(task1->real_fs, task2->real_fs, KCMP_FS); break; case KCMP_SIGHAND: ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND); diff --git a/kernel/umh.c b/kernel/umh.c index 48117c5..6e2c7bb 100644 --- a/kernel/umh.c +++ b/kernel/umh.c @@ -71,10 +71,8 @@ static int call_usermodehelper_exec_async(void *data) spin_unlock_irq(¤t->sighand->siglock); /* - * Initial kernel threads share ther FS with init, in order to - * get the init root directory. But we've now created a new - * thread that is going to execve a user process and has its own - * 'struct fs_struct'. Reset umask to the default. + * Usermodehelper threads get a copy of userspace init's + * fs_struct. Reset umask to the default. */ current->fs->umask = 0022; diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 10ed942..7794740 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1197,17 +1197,12 @@ static struct sock *unix_find_bsd(struct sockaddr_un *sunaddr, int addr_len, unix_mkname_bsd(sunaddr, addr_len); if (flags & SOCK_COREDUMP) { - struct path root; - - task_lock(&init_task); - get_fs_root(init_task.fs, &root); - task_unlock(&init_task); - - scoped_with_kernel_creds() - err = vfs_path_lookup(root.dentry, root.mnt, sunaddr->sun_path, - LOOKUP_BENEATH | LOOKUP_NO_SYMLINKS | - LOOKUP_NO_MAGICLINKS, &path); - path_put(&root); + scoped_with_init_fs() { + scoped_with_kernel_creds() + err = kern_path(sunaddr->sun_path, + LOOKUP_NO_SYMLINKS | + LOOKUP_NO_MAGICLINKS, &path); + } if (err) goto fail; } else {