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

[Eric Biggers]

From: Eric Biggers <ebigg...@google.com>

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: sta...@vger.kernel.org # v4.10+
Reported-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Eric Biggers <ebigg...@google.com>
---
 crypto/lrw.c | 7 +++++--
 crypto/xts.c | 7 +++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/crypto/lrw.c b/crypto/lrw.c
index ecd8474018e3..3ea095adafd9 100644
--- a/crypto/lrw.c
+++ b/crypto/lrw.c
@@ -286,8 +286,11 @@ static int init_crypt(struct skcipher_request *req, 
crypto_completion_t done)
 
        subreq->cryptlen = LRW_BUFFER_SIZE;
        if (req->cryptlen > LRW_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;
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;
-- 
2.12.1.500.gab5fba24ee-goog