Merge branch 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

287c55ed · Linus Torvalds <[email protected]> · 2019-08-19 16:17:59 -07:00

Pull kernel thread signal handling fix from Eric Biederman:
 "I overlooked the fact that kernel threads are created with all signals
  set to SIG_IGN, and accidentally caused a regression in cifs and drbd
  when replacing force_sig with send_sig.

  This is my fix for that regression. I add a new function
  allow_kernel_signal which allows kernel threads to receive signals
  sent from the kernel, but continues to ignore all signals sent from
  userspace. This ensures the user space interface for cifs and drbd
  remain the same.

  These kernel threads depend on blocking networking calls which block
  until something is received or a signal is pending. Making receiving
  of signals somewhat necessary for these kernel threads.

  Perhaps someday we can cleanup those interfaces and remove
  allow_kernel_signal. If not allow_kernel_signal is pretty trivial and
  clearly documents what is going on so I don't think we will mind
  carrying it"

* 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  signal: Allow cifs and drbd to receive their terminating signals

Commit: 287c55ed7df531c30f7a5093120339193dc7f166
Parents: 06821504 · 33da8e7c

Merge commit. Changes below are compared with the first parent: 06821504.

Changes

4 files changed · +22 −2

File	Status	Add	Del	Content
drivers/block/drbd/drbd_main.c	modified	+2	−0	View file
fs/cifs/connect.c	modified	+1	−1	View file
include/linux/signal.h	modified	+14	−1	View file
kernel/signal.c	modified	+5	−0	View file

drivers/block/drbd/drbd_main.c

View file

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 9bd4ddd..5b24876 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -322,6 +322,8 @@ static int drbd_thread_setup(void *arg)
 		 thi->name[0],
 		 resource->name);
 
+	allow_kernel_signal(DRBD_SIGKILL);
+	allow_kernel_signal(SIGXCPU);
 restart:
 	retval = thi->function(thi);
 

fs/cifs/connect.c

View file

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index a15a6e7..1795e80 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1113,7 +1113,7 @@ cifs_demultiplex_thread(void *p)
 		mempool_resize(cifs_req_poolp, length + cifs_min_rcv);
 
 	set_freezable();
-	allow_signal(SIGKILL);
+	allow_kernel_signal(SIGKILL);
 	while (server->tcpStatus != CifsExiting) {
 		if (try_to_freeze())
 			continue;

include/linux/signal.h

View file

diff --git a/include/linux/signal.h b/include/linux/signal.h
index b5d9948..1a5f883 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -282,6 +282,9 @@ extern void signal_setup_done(int failed, struct ksignal *ksig, int stepping);
 extern void exit_signals(struct task_struct *tsk);
 extern void kernel_sigaction(int, __sighandler_t);
 
+#define SIG_KTHREAD ((__force __sighandler_t)2)
+#define SIG_KTHREAD_KERNEL ((__force __sighandler_t)3)
+
 static inline void allow_signal(int sig)
 {
 	/*
@@ -289,7 +292,17 @@ static inline void allow_signal(int sig)
 	 * know it'll be handled, so that they don't get converted to
 	 * SIGKILL or just silently dropped.
 	 */
-	kernel_sigaction(sig, (__force __sighandler_t)2);
+	kernel_sigaction(sig, SIG_KTHREAD);
+}
+
+static inline void allow_kernel_signal(int sig)
+{
+	/*
+	 * Kernel threads handle their own signals. Let the signal code
+	 * know signals sent by the kernel will be handled, so that they
+	 * don't get silently dropped.
+	 */
+	kernel_sigaction(sig, SIG_KTHREAD_KERNEL);
 }
 
 static inline void disallow_signal(int sig)

kernel/signal.c

View file

diff --git a/kernel/signal.c b/kernel/signal.c
index e667be6..534fec2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -90,6 +90,11 @@ static bool sig_task_ignored(struct task_struct *t, int sig, bool force)
 	    handler == SIG_DFL && !(force && sig_kernel_only(sig)))
 		return true;
 
+	/* Only allow kernel generated signals to this kthread */
+	if (unlikely((t->flags & PF_KTHREAD) &&
+		     (handler == SIG_KTHREAD_KERNEL) && !force))
+		return true;
+
 	return sig_handler_ignored(handler, sig);
 }
 