projects/linux·commit 86b62a2c

aio: fix io_setup/io_destroy race

86b62a2c · Al Viro <[email protected]> · 2012-03-07 05:16:35 +00:00

Have ioctx_alloc() return an extra reference, so that caller would drop it
on success and not bother with re-grabbing it on failure exit.  The current
code is obviously broken - io_destroy() from another thread that managed
to guess the address io_setup() would've returned would free ioctx right
under us; gets especially interesting if aio_context_t * we pass to
io_setup() points to PROT_READ mapping, so put_user() fails and we end
up doing io_destroy() on kioctx another thread has just got freed...

Signed-off-by: Al Viro <[email protected]>
Acked-by: Benjamin LaHaise <[email protected]>
Reviewed-by: Jeff Moyer <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>
Commit
86b62a2cb4fc09037bbce2959d2992962396fd7f
Parents
86e06008

Changes

1 files changed · +4 −4

FileStatusAddDelContent
fs/aio.cmodified+4−4View file

fs/aio.c

View file
diff --git a/fs/aio.c b/fs/aio.c
index 67e4b90..f6578cb 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -273,7 +273,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
mm = ctx->mm = current->mm;
atomic_inc(&mm->mm_count);
- atomic_set(&ctx->users, 1);
+ atomic_set(&ctx->users, 2);
spin_lock_init(&ctx->ctx_lock);
spin_lock_init(&ctx->ring_info.ring_lock);
init_waitqueue_head(&ctx->wait);
@@ -1338,10 +1338,10 @@ SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
ret = PTR_ERR(ioctx);
if (!IS_ERR(ioctx)) {
ret = put_user(ioctx->user_id, ctxp);
- if (!ret)
+ if (!ret) {
+ put_ioctx(ioctx);
return 0;
-
- get_ioctx(ioctx); /* io_destroy() expects us to hold a ref */
+ }
io_destroy(ioctx);
}