[3.13.y-ckt stable] Patch "crypto: af_alg - fix backlog handling" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    crypto: af_alg - fix backlog handling

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d5d6b7ddc235ade9694b978558931bd13431f78a Mon Sep 17 00:00:00 2001
From: Rabin Vincent <rabin.vincent at axis.com>
Date: Fri, 19 Dec 2014 13:36:08 +0100
Subject: crypto: af_alg - fix backlog handling

commit 7e77bdebff5cb1e9876c561f69710b9ab8fa1f7e upstream.

If a request is backlogged, it's complete() handler will get called
twice: once with -EINPROGRESS, and once with the final error code.

af_alg's complete handler, unlike other users, does not handle the
-EINPROGRESS but instead always completes the completion that recvmsg()
is waiting on.  This can lead to a return to user space while the
request is still pending in the driver.  If userspace closes the sockets
before the requests are handled by the driver, this will lead to
use-after-frees (and potential crashes) in the kernel due to the tfm
having been freed.

The crashes can be easily reproduced (for example) by reducing the max
queue length in cryptod.c and running the following (from
http://www.chronox.de/libkcapi.html) on AES-NI capable hardware:

 $ while true; do kcapi -x 1 -e -c '__ecb-aes-aesni' \
    -k 00000000000000000000000000000000 \
    -p 00000000000000000000000000000000 >/dev/null & done

Signed-off-by: Rabin Vincent <rabin.vincent at axis.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 crypto/af_alg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 6a3ad80..1de4bee 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -449,6 +449,9 @@ void af_alg_complete(struct crypto_async_request *req, int err)
 {
 	struct af_alg_completion *completion = req->data;

+	if (err == -EINPROGRESS)
+		return;
+
 	completion->err = err;
 	complete(&completion->completion);
 }
--
1.9.1