[CRYPTO] xcbc: Fix crash with IPsec

When using aes-xcbc-mac for authentication in IPsec, 
the kernel crashes. It seems this algorithm doesn't 
account for the space IPsec may make in scatterlist for authtag.
Thus when crypto_xcbc_digest_update2() gets called,
nbytes may be less than sg[i].length. 
Since nbytes is an unsigned number, it wraps
at the end of the loop allowing us to go back 
into loop and causing crash in memcpy.

I used update function in digest.c to model this fix.
Please let me know if it looks ok.

Signed-off-by: Joy Latten <latten@austin.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 5 insertions, 1 deletions

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
index 86727403e5ab..2feb0f239c38 100644
--- a/crypto/xcbc.c
+++ b/crypto/xcbc.c
@@ -124,6 +124,11 @@ static int crypto_xcbc_digest_update2(struct hash_desc *pdesc,
                 unsigned int offset = sg[i].offset;
                 unsigned int slen = sg[i].length;
 
+                if (unlikely(slen > nbytes))
+                        slen = nbytes;
+
+                nbytes -= slen;
+
                 while (slen > 0) {
                         unsigned int len = min(slen, ((unsigned int)(PAGE_SIZE)) - offset);
                         char *p = crypto_kmap(pg, 0) + offset;
@@ -177,7 +182,6 @@ static int crypto_xcbc_digest_update2(struct hash_desc *pdesc,
                         offset = 0;
                         pg++;
                 }
-                nbytes-=sg[i].length;
                 i++;
         } while (nbytes>0);