[PATCH 3.16 099/328] crypto: blkcipher - fix crash flushing dcache in error path

Ben Hutchings
2018-12-09T21:59:49Z

From: Eric Biggers <ebiggers@google.com>

commit 0868def3e4100591e7a1fdbf3eed1439cc8f7ca3 upstream.

Like the skcipher_walk case:

scatterwalk_done() is only meant to be called after a nonzero number of
bytes have been processed, since scatterwalk_pagedone() will flush the
dcache of the *previous* page. But in the error case of
blkcipher_walk_done(), e.g. if the input wasn't an integer number of
blocks, scatterwalk_done() was actually called after advancing 0 bytes.
This caused a crash ("BUG: unable to handle kernel paging request")
during '!PageSlab(page)' on architectures like arm and arm64 that define
ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, provided that the input was
page-aligned as in that case walk->offset == 0.

Fix it by reorganizing blkcipher_walk_done() to skip the
scatterwalk_advance() and scatterwalk_done() if an error has occurred.

This bug was found by syzkaller fuzzing.

Reproducer, assuming ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE:

#include <linux/if_alg.h>
#include <sys/socket.h>
#include <unistd.h>

int main()
{
struct sockaddr_alg addr = {
.salg_type = "skcipher",
.salg_name = "ecb(aes-generic)",
};
char buffer[4096] __attribute__((aligned(4096))) = { 0 };
int fd;

fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
bind(fd, (void *)&addr, sizeof(addr));
setsockopt(fd, SOL_ALG, ALG_SET_KEY, buffer, 16);
fd = accept(fd, NULL, NULL);
write(fd, buffer, 15);
read(fd, buffer, 15);
}

Reported-by: Liu Chao <liuchao741@huawei.com>
Fixes: 5cde0af2a982 ("[CRYPTO] cipher: Added block cipher type")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
crypto/blkcipher.c | 54 ++++++++++++++++++++++------------------------
1 file changed, 26 insertions(+), 28 deletions(-)

--- a/crypto/blkcipher.c
+++ b/crypto/blkcipher.c
@@ -70,19 +70,18 @@ static inline u8 *blkcipher_get_spot(u8
return max(start, end_page);
}

-static inline unsigned int blkcipher_done_slow(struct blkcipher_walk *walk,
- unsigned int bsize)
+static inline void blkcipher_done_slow(struct blkcipher_walk *walk,
+ unsigned int bsize)
{
u8 *addr;

addr = (u8 *)ALIGN((unsigned long)walk->buffer, walk->alignmask + 1);
addr = blkcipher_get_spot(addr, bsize);
scatterwalk_copychunks(addr, &walk->out, bsize, 1);
- return bsize;
}

-static inline unsigned int blkcipher_done_fast(struct blkcipher_walk *walk,
- unsigned int n)
+static inline void blkcipher_done_fast(struct blkcipher_walk *walk,
+ unsigned int n)
{
if (walk->flags & BLKCIPHER_WALK_COPY) {
blkcipher_map_dst(walk);
@@ -96,49 +95,48 @@ static inline unsigned int blkcipher_don

scatterwalk_advance(&walk->in, n);
scatterwalk_advance(&walk->out, n);
-
- return n;
}

int blkcipher_walk_done(struct blkcipher_desc *desc,
struct blkcipher_walk *walk, int err)
{
- unsigned int nbytes = 0;
+ unsigned int n; /* bytes processed */
+ bool more;

- if (likely(err >= 0)) {
- unsigned int n = walk->nbytes - err;
+ if (unlikely(err < 0))
+ goto finish;

- if (likely(!(walk->flags & BLKCIPHER_WALK_SLOW)))
- n = blkcipher_done_fast(walk, n);
- else if (WARN_ON(err)) {
+ n = walk->nbytes - err;
+ walk->total -= n;
+ more = (walk->total != 0);
+
+ if (likely(!(walk->flags & BLKCIPHER_WALK_SLOW))) {
+ blkcipher_done_fast(walk, n);
+ } else {
+ if (WARN_ON(err)) {
+ /* unexpected case; didn't process all bytes */
err = -EINVAL;
- goto err;
- } else
- n = blkcipher_done_slow(walk, n);
-
- nbytes = walk->total - n;
- err = 0;
+ goto finish;
+ }
+ blkcipher_done_slow(walk, n);
}

- scatterwalk_done(&walk->in, 0, nbytes);
- scatterwalk_done(&walk->out, 1, nbytes);
-
-err:
- walk->total = nbytes;
- walk->nbytes = nbytes;
+ scatterwalk_done(&walk->in, 0, more);
+ scatterwalk_done(&walk->out, 1, more);

- if (nbytes) {
+ if (more) {
crypto_yield(desc->flags);
return blkcipher_walk_next(desc, walk);
}
-
+ err = 0;
+finish:
+ walk->nbytes = 0;
if (walk->iv != desc->info)
memcpy(desc->info, walk->iv, walk->ivsize);
if (walk->buffer != walk->page)
kfree(walk->buffer);
if (walk->page)
free_page((unsigned long)walk->page);
-
return err;
}
EXPORT_SYMBOL_GPL(blkcipher_walk_done);