Commit a4b8e71b authored by Jiri Slaby's avatar Jiri Slaby Committed by David S. Miller
Browse files

net: sctp, forbid negative length

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

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 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: default avatarJiri Slaby <>
Cc: Vlad Yasevich <>
Cc: Neil Horman <>
Cc: "David S. Miller" <>
Acked-by: default avatarNeil Horman <>
Signed-off-by: default avatarDavid S. Miller <>
parent 235bde1e
......@@ -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;
switch (optname) {
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