linux-kernel - [PATCH] algif_skcipher: Avoid crash if buffer is not multiple of cipher block size

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Date:	Sun, 14 Apr 2013 18:12:32 +0200
From:	Milan Broz <gmazyland@...il.com>
To:	linux-crypto@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Milan Broz <gmazyland@...il.com>
Subject: [PATCH] algif_skcipher: Avoid crash if buffer is not multiple of cipher block size

When user requests encryption (or decryption) of block which
is not aligned to cipher block size through userspace crypto
interface, an OOps like this can happen:

[  112.738285] BUG: unable to handle kernel paging request at e1c44840
[  112.738407] IP: [<c121f473>] scatterwalk_done+0x53/0x70
...
[  112.740515] Call Trace:
[  112.740588]  [<c1221d30>] blkcipher_walk_done+0x160/0x1e0
[  112.740663]  [<c12220c8>] blkcipher_walk_next+0x318/0x3c0
[  112.740737]  [<c12221e0>] blkcipher_walk_first+0x70/0x160
[  112.740811]  [<c1222327>] blkcipher_walk_virt+0x17/0x20
[  112.740886]  [<e0ce4249>] cbc_encrypt+0x29/0x100 [aesni_intel]
[  112.740968]  [<c1029f73>] ? get_user_pages_fast+0x123/0x150
[  112.741046]  [<c106e7db>] ? trace_hardirqs_on+0xb/0x10
[  112.741119]  [<e081e1c9>] __ablk_encrypt+0x39/0x40 [ablk_helper]
[  112.741198]  [<e081e1ea>] ablk_encrypt+0x1a/0x70 [ablk_helper]
[  112.741275]  [<e0f715ac>] skcipher_recvmsg+0x20c/0x400 [algif_skcipher]
[  112.741359]  [<c1056a1d>] ? sched_clock_cpu+0x11d/0x1a0
[  112.741435]  [<c10a5eb9>] ? find_get_page+0x79/0xc0
[  112.741509]  [<c135e034>] sock_aio_read+0x104/0x140
[  112.741580]  [<c10be638>] ? __do_fault+0x248/0x420
[  112.741650]  [<c10d3d27>] do_sync_read+0x97/0xd0
[  112.741719]  [<c10d45ed>] vfs_read+0x11d/0x140
[  112.741789]  [<c135f683>] ? sys_socketcall+0x2a3/0x320
[  112.741861]  [<c10d4762>] sys_read+0x42/0x90
[  112.742578]  [<c141c27a>] sysenter_do_call+0x12/0x32

Patch fixes it by simply rejecting buffer which is not multiple of cipher block.

(Bug is present in all stable kernels as well.)

Signed-off-by: Milan Broz <gmazyland@...il.com>
---
 crypto/algif_skcipher.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 6a6dfc0..5f7713b 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -463,7 +463,7 @@ static int skcipher_recvmsg(struct kiocb *unused, struct socket *sock,
 				used -= used % bs;
 
 			err = -EINVAL;
-			if (!used)
+			if (!used || used % bs)
 				goto free;
 
 			ablkcipher_request_set_crypt(&ctx->req, sg,
-- 
1.7.10.4

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