• Eric Biggers's avatar
    crypto: vmac - separate tfm and request context · 990e4778
    Eric Biggers authored
    commit bb296481 upstream.
    
    syzbot reported a crash in vmac_final() when multiple threads
    concurrently use the same "vmac(aes)" transform through AF_ALG.  The bug
    is pretty fundamental: the VMAC template doesn't separate per-request
    state from per-tfm (per-key) state like the other hash algorithms do,
    but rather stores it all in the tfm context.  That's wrong.
    
    Also, vmac_final() incorrectly zeroes most of the state including the
    derived keys and cached pseudorandom pad.  Therefore, only the first
    VMAC invocation with a given key calculates the correct digest.
    
    Fix these bugs by splitting the per-tfm state from the per-request state
    and using the proper init/update/final sequencing for requests.
    
    Reproducer for the crash:
    
        #include <linux/if_alg.h>
        #include <sys/socket.h>
        #include <unistd.h>
    
        int main()
        {
                int fd;
                struct sockaddr_alg addr = {
                        .salg_type = "hash",
                        .salg_name = "vmac(aes)",
                };
                char buf[256] = { 0 };
    
                fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
                bind(fd, (void *)&addr, sizeof(addr));
                setsockopt(fd, SOL_ALG, ALG_SET_KEY, buf, 16);
                fork();
                fd = accept(fd, NULL, NULL);
                for (;;)
                        write(fd, buf, 256);
        }
    
    The immediate cause of the crash is that vmac_ctx_t.partial_size exceeds
    VMAC_NHBYTES, causing vmac_final() to memset() a negative length.
    
    Reported-by: syzbot+264bca3a6e8d645550d3@syzkaller.appspotmail.com
    Fixes: f1939f7c ("crypto: vmac - New hash algorithm for intel_txt support")
    Cc: <stable@vger.kernel.org> # v2.6.32+
    Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    990e4778