crypto: blkcipher - fix crash flushing dcache in error path

BugLink: https://bugs.launchpad.net/bugs/1835845
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")
Cc: <stable@vger.kernel.org> # v2.6.19+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/crypto/blkcipher.c b/crypto/blkcipher.c
index 6c43a0a17a5514b46f9300e21ded357defb39d50..d84c6920ada9fe0b814df033b066edcb1e06e22a 100644 (file)
--- a/crypto/blkcipher.c
+++ b/crypto/blkcipher.c
@@ -71,19 +71,18 @@ static inline u8 *blkcipher_get_spot(u8 *start, unsigned int len)
        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);
@@ -97,49 +96,48 @@ static inline unsigned int blkcipher_done_fast(struct blkcipher_walk *walk,
 
        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)) {
-                       err = -EINVAL;
-                       goto err;
-               } else
-                       n = blkcipher_done_slow(walk, n);
+       n = walk->nbytes - err;
+       walk->total -= n;
+       more = (walk->total != 0);
 
-               nbytes = walk->total - n;
-               err = 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 finish;
+               }
+               blkcipher_done_slow(walk, n);
        }
 
-       scatterwalk_done(&walk->in, 0, nbytes);
-       scatterwalk_done(&walk->out, 1, nbytes);
+       scatterwalk_done(&walk->in, 0, more);
+       scatterwalk_done(&walk->out, 1, more);
 
-err:
-       walk->total = nbytes;
-       walk->nbytes = nbytes;
-
-       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);