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aio: fix io_setup/io_destroy race 

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 <viro@zeniv.linux.org.uk>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Al Viro 2012-03-07 05:16:35 +00:00 committed by Linus Torvalds
parent 86e0600833
commit 86b62a2cb4
1 changed files with 4 additions and 4 deletions
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8
fs/aio.c
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@ -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);
}