On Fri, Oct 21, 2016 at 02:13:24PM +0200, Jiri Slaby wrote:
> Most of getsockopt handlers in net/sctp/socket.c check len against
> sizeof some structure like:
> if (len < sizeof(int))
> return -EINVAL;
>
> On the first look, the check seems to be correct. But since len is int
> and sizeof returns size_t, int gets promoted to unsigned size_t too. So
> the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
> false.
>
> Fix this in sctp by explicitly checking len < 0 before any getsockopt
> handler is called.
>
> Note that sctp_getsockopt_events already handled the negative case.
> Since we added the < 0 check elsewhere, this one can be removed.
>
> If not checked, this is the result:
> UBSAN: Undefined behaviour in ../mm/page_alloc.c:2722:19
> shift exponent 52 is too large for 32-bit type 'int'
> CPU: 1 PID: 24535 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
> 0000000000000000 ffff88006d99f2a8 ffffffffb2f7bdea 0000000041b58ab3
> ffffffffb4363c14 ffffffffb2f7bcde ffff88006d99f2d0 ffff88006d99f270
> 0000000000000000 0000000000000000 0000000000000034 ffffffffb5096422
> Call Trace:
> [<ffffffffb3051498>] ? __ubsan_handle_shift_out_of_bounds+0x29c/0x300
> ...
> [<ffffffffb273f0e4>] ? kmalloc_order+0x24/0x90
> [<ffffffffb27416a4>] ? kmalloc_order_trace+0x24/0x220
> [<ffffffffb2819a30>] ? __kmalloc+0x330/0x540
> [<ffffffffc18c25f4>] ? sctp_getsockopt_local_addrs+0x174/0xca0 [sctp]
> [<ffffffffc18d2bcd>] ? sctp_getsockopt+0x10d/0x1b0 [sctp]
> [<ffffffffb37c1219>] ? sock_common_getsockopt+0xb9/0x150
> [<ffffffffb37be2f5>] ? SyS_getsockopt+0x1a5/0x270
>
> Signed-off-by: Jiri Slaby <jsl...@suse.cz>
> Cc: Vlad Yasevich <vyasev...@gmail.com>
> Cc: Neil Horman <nhor...@tuxdriver.com>
> Cc: "David S. Miller" <da...@davemloft.net>
> Cc: linux-s...@vger.kernel.org
> Cc: netdev@vger.kernel.org
> ---
> net/sctp/socket.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index fb02c7033307..9fbb6feb8c27 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4687,7 +4687,7 @@ static int sctp_getsockopt_disable_fragments(struct
> sock *sk, int len,
> static int sctp_getsockopt_events(struct sock *sk, int len, char __user
> *optval,
> int __user *optlen)
> {
> - if (len <= 0)
> + if (len == 0)
> return -EINVAL;
> if (len > sizeof(struct sctp_event_subscribe))
> len = sizeof(struct sctp_event_subscribe);
> @@ -6430,6 +6430,9 @@ static int sctp_getsockopt(struct sock *sk, int level,
> int optname,
> if (get_user(len, optlen))
> return -EFAULT;
>
> + if (len < 0)
> + return -EINVAL;
> +
> lock_sock(sk);
>
> switch (optname) {
> --
> 2.10.1
>
>
Acked-by: Neil Horman <nhor...@tuxdriver.com>
