• Eric Biggers's avatar
    crypto: salsa20 - fix blkcipher_walk API usage · c32e053a
    Eric Biggers authored
    commit ecaaab56 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: 's avatarsyzbot <syzkaller@googlegroups.com>
    Fixes: eb6f13eb ("[CRYPTO] salsa20_generic: Fix multi-page processing")
    Signed-off-by: 's avatarEric Biggers <ebiggers@google.com>
    Signed-off-by: 's avatarHerbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    c32e053a