linux-kernel - [PATCH 3.10 128/139] crypto: AF_ALG - remove SGL terminator indicator when chaining

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Message-Id: <1509571624-5001-29-git-send-email-w@1wt.eu>
Date:   Wed,  1 Nov 2017 22:26:53 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Stephan Mueller <smueller@...onox.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 128/139] crypto: AF_ALG - remove SGL terminator indicator when chaining

From: Stephan Mueller <smueller@...onox.de>

commit 1d4ba7f963a93a2207fd103d4a36df1b5aeefea2 upstream.

Fixed differently upstream as commit 2d97591ef43d ("crypto: af_alg - consolidation of duplicate code")

The SGL is MAX_SGL_ENTS + 1 in size. The last SG entry is used for the
chaining and is properly updated with the sg_chain invocation. During
the filling-in of the initial SG entries, sg_mark_end is called for each
SG entry. This is appropriate as long as no additional SGL is chained
with the current SGL. However, when a new SGL is chained and the last
SG entry is updated with sg_chain, the last but one entry still contains
the end marker from the sg_mark_end. This end marker must be removed as
otherwise a walk of the chained SGLs will cause a NULL pointer
dereference at the last but one SG entry, because sg_next will return
NULL.

The patch only applies to all kernels up to and including 4.13. The
patch 2d97591ef43d0587be22ad1b0d758d6df4999a0b added to 4.14-rc1
introduced a complete new code base which addresses this bug in
a different way. Yet, that patch is too invasive for stable kernels
and was therefore not marked for stable.

Fixes: 8ff590903d5fc ("crypto: algif_skcipher - User-space interface for skcipher operations")
Signed-off-by: Stephan Mueller <smueller@...onox.de>
Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 crypto/algif_skcipher.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index ea05c53..8e27474 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -92,8 +92,10 @@ static int skcipher_alloc_sgl(struct sock *sk)
 		sg_init_table(sgl->sg, MAX_SGL_ENTS + 1);
 		sgl->cur = 0;

-		if (sg)
+		if (sg) {
 			scatterwalk_sg_chain(sg, MAX_SGL_ENTS + 1, sgl->sg);
+			sg_unmark_end(sg + (MAX_SGL_ENTS - 1));
+		}

 		list_add_tail(&sgl->list, &ctx->tsgl);
 	}
-- 
2.8.0.rc2.1.gbe9624a