[PATCH 4.4 002/115] crypto: salsa20 - fix blkcipher_walk API usage

Greg Kroah-Hartman
2017-12-18T15:52:27Z

From: Eric Biggers <ebiggers@google.com>

commit ecaaab5649781c5a0effdaf298a925063020500e upstream.

When asked to encrypt or decrypt 0 bytes, both the generic and x86
implementations of Salsa20 crash in blkcipher_walk_done(), either when
doing 'kfree(walk->buffer)' or 'free_page((unsigned long)walk->page)',
because walk->buffer and walk->page have not been initialized.

The bug is that Salsa20 is calling blkcipher_walk_done() even when
nothing is in 'walk.nbytes'. But blkcipher_walk_done() is only meant to
be called when a nonzero number of bytes have been provided.

The broken code is part of an optimization that tries to make only one
call to salsa20_encrypt_bytes() to process inputs that are not evenly
divisible by 64 bytes. To fix the bug, just remove this "optimization"
and use the blkcipher_walk API the same way all the other users do.

Reproducer:

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

int main()
{
int algfd, reqfd;
struct sockaddr_alg addr = {
.salg_type = "skcipher",
.salg_name = "salsa20",
};
char key[16] = { 0 };

algfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
bind(algfd, (void *)&addr, sizeof(addr));
reqfd = accept(algfd, 0, 0);
setsockopt(algfd, SOL_ALG, ALG_SET_KEY, key, sizeof(key));
read(reqfd, key, sizeof(key));
}

Reported-by: syzbot <syzkaller@googlegroups.com>
Fixes: eb6f13eb9f81 ("[CRYPTO] salsa20_generic: Fix multi-page processing")
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>

---
arch/x86/crypto/salsa20_glue.c | 7 -------
crypto/salsa20_generic.c | 7 -------
2 files changed, 14 deletions(-)

--- a/arch/x86/crypto/salsa20_glue.c
+++ b/arch/x86/crypto/salsa20_glue.c
@@ -59,13 +59,6 @@ static int encrypt(struct blkcipher_desc

salsa20_ivsetup(ctx, walk.iv);

- if (likely(walk.nbytes == nbytes))
- {
- salsa20_encrypt_bytes(ctx, walk.src.virt.addr,
- walk.dst.virt.addr, nbytes);
- return blkcipher_walk_done(desc, &walk, 0);
- }
-
while (walk.nbytes >= 64) {
salsa20_encrypt_bytes(ctx, walk.src.virt.addr,
walk.dst.virt.addr,
--- a/crypto/salsa20_generic.c
+++ b/crypto/salsa20_generic.c
@@ -188,13 +188,6 @@ static int encrypt(struct blkcipher_desc

salsa20_ivsetup(ctx, walk.iv);

- if (likely(walk.nbytes == nbytes))
- {
- salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
- walk.src.virt.addr, nbytes);
- return blkcipher_walk_done(desc, &walk, 0);
- }
-
while (walk.nbytes >= 64) {
salsa20_encrypt_bytes(ctx, walk.dst.virt.addr,
walk.src.virt.addr,