crypto: salsa20 - fix blkcipher_walk API usage
authorEric Biggers <ebiggers@google.com>
Wed, 29 Nov 2017 04:56:59 +0000 (20:56 -0800)
committerBen Hutchings <ben@decadent.org.uk>
Mon, 1 Jan 2018 20:51:05 +0000 (20:51 +0000)
commita1eb10d948c39388c5dea527aa4e76ac90a6a7e1
tree0a6672133d6a66620a626e5c1ea6dd84ebd79477
parent26a8a3c531ae847048ee9126f07cb07424bd4724
crypto: salsa20 - fix blkcipher_walk API usage

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: Ben Hutchings <ben@decadent.org.uk>
arch/x86/crypto/salsa20_glue.c
crypto/salsa20_generic.c