[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>

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
index 8672740..2feb0f2 100644 (file)
--- 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);