[PATCH 4.10 44/81] crypto: xts,lrw - fix out-of-bounds write after kmalloc failure

[Greg Kroah-Hartman]

4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@xxxxxxxxxx>

commit 9df0eb180c2074451f25556eb566d89c7057c2ac upstream.

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")
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 crypto/lrw.c |    7 +++++--
 crypto/xts.c |    7 +++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

--- a/crypto/lrw.c
+++ b/crypto/lrw.c
@@ -286,8 +286,11 @@ static int init_crypt(struct skcipher_re
 
 	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;
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -230,8 +230,11 @@ static int init_crypt(struct skcipher_re
 
 	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;