• Jiri Slaby's avatar
    crypto: algif_hash - avoid zero-sized array · 62071194
    Jiri Slaby authored
    With this reproducer:
      struct sockaddr_alg alg = {
              .salg_family = 0x26,
              .salg_type = "hash",
              .salg_feat = 0xf,
              .salg_mask = 0x5,
              .salg_name = "digest_null",
      };
      int sock, sock2;
    
      sock = socket(AF_ALG, SOCK_SEQPACKET, 0);
      bind(sock, (struct sockaddr *)&alg, sizeof(alg));
      sock2 = accept(sock, NULL, NULL);
      setsockopt(sock, SOL_ALG, ALG_SET_KEY, "\x9b\xca", 2);
      accept(sock2, NULL, NULL);
    
    ==== 8< ======== 8< ======== 8< ======== 8< ====
    
    one can immediatelly see an UBSAN warning:
    UBSAN: Undefined behaviour in crypto/algif_hash.c:187:7
    variable length array bound value 0 <= 0
    CPU: 0 PID: 15949 Comm: syz-executor Tainted: G            E      4.4.30-0-default #1
    ...
    Call Trace:
    ...
     [<ffffffff81d598fd>] ? __ubsan_handle_vla_bound_not_positive+0x13d/0x188
     [<ffffffff81d597c0>] ? __ubsan_handle_out_of_bounds+0x1bc/0x1bc
     [<ffffffffa0e2204d>] ? hash_accept+0x5bd/0x7d0 [algif_hash]
     [<ffffffffa0e2293f>] ? hash_accept_nokey+0x3f/0x51 [algif_hash]
     [<ffffffffa0e206b0>] ? hash_accept_parent_nokey+0x4a0/0x4a0 [algif_hash]
     [<ffffffff8235c42b>] ? SyS_accept+0x2b/0x40
    
    It is a correct warning, as hash state is propagated to accept as zero,
    but creating a zero-length variable array is not allowed in C.
    
    Fix this as proposed by Herbert -- do "?: 1" on that site. No sizeof or
    similar happens in the code there, so we just allocate one byte even
    though we do not use the array.
    Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
    Cc: Herbert Xu <herbert@gondor.apana.org.au>
    Cc: "David S. Miller" <davem@davemloft.net> (maintainer:CRYPTO API)
    Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    62071194
algif_hash.c 10.4 KB