crypto: xts,lrw - fix out-of-bounds write after kmalloc failure

In the generic XTS and LRW algorithms, for input data > 128 bytes, a
temporary buffer is allocated to hold the values to be XOR'ed with the
data before and after encryption or decryption.  If the allocation
fails, the fixed-size buffer embedded in the request buffer is meant to
be used as a fallback --- resulting in more calls to the ECB algorithm,
but still producing the correct result.  However, we weren't correctly
limiting subreq->cryptlen in this case, resulting in pre_crypt()
overrunning the embedded buffer.  Fix this by setting subreq->cryptlen
correctly.

Fixes: f1c131b45410 ("crypto: xts - Convert to skcipher")
Fixes: 700cb3f5fe75 ("crypto: lrw - Convert to skcipher")
Cc: stable@vger.kernel.org # v4.10+
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 5 insertions, 2 deletions

diff --git a/crypto/xts.c b/crypto/xts.c
index baeb34dd8582..c976bfac29da 100644
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -230,8 +230,11 @@ static int init_crypt(struct skcipher_request *req, crypto_completion_t done)
 
         subreq->cryptlen = XTS_BUFFER_SIZE;
         if (req->cryptlen > XTS_BUFFER_SIZE) {
-                subreq->cryptlen = min(req->cryptlen, (unsigned)PAGE_SIZE);
-                rctx->ext = kmalloc(subreq->cryptlen, gfp);
+                unsigned int n = min(req->cryptlen, (unsigned int)PAGE_SIZE);
+
+                rctx->ext = kmalloc(n, gfp);
+                if (rctx->ext)
+                        subreq->cryptlen = n;
         }
 
         rctx->src = req->src;