linux-kernel - [ 03/41] aio: fix io_setup/io

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Message-Id: <20120316233810.863794674@linuxfoundation.org>
Date:	Fri, 16 Mar 2012 16:38:13 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Al Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: [ 03/41] aio: fix io_setup/io_destroy race

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@...IV.linux.org.uk>

commit 86b62a2cb4fc09037bbce2959d2992962396fd7f upstream.

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@...iv.linux.org.uk>
Acked-by: Benjamin LaHaise <bcrl@...ck.org>
Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/aio.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -273,7 +273,7 @@ static struct kioctx *ioctx_alloc(unsign
 	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_e
 	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);
 	}
 


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