[PATCH 3.2 167/199] net: sctp, forbid negative length

From: Ben Hutchings
Date: Fri Mar 10 2017 - 06:57:49 EST

3.2.87-rc1 review patch. If anyone has any objections, please let me know.


From: Jiri Slaby <jslaby@xxxxxxx>

[ Upstream commit a4b8e71b05c27bae6bad3bdecddbc6b68a3ad8cf ]

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 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 <jslaby@xxxxxxx>
Cc: Vlad Yasevich <vyasevich@xxxxxxxxx>
Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: linux-sctp@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
net/sctp/socket.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4193,7 +4193,7 @@ static int sctp_getsockopt_disable_fragm
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);
@@ -5586,6 +5586,9 @@ SCTP_STATIC int sctp_getsockopt(struct s
if (get_user(len, optlen))
return -EFAULT;

+ if (len < 0)
+ return -EINVAL;

switch (optname) {