Patch "RDS: Check cmsg_len before dereferencing CMSG_DATA" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

RDS: Check cmsg_len before dereferencing CMSG_DATA

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rds-check-cmsg_len-before-dereferencing-cmsg_data.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Avinash Repaka <[email protected]>
Date: Thu, 21 Dec 2017 20:17:04 -0800
Subject: RDS: Check cmsg_len before dereferencing CMSG_DATA

From: Avinash Repaka <[email protected]>

[ Upstream commit 14e138a86f6347c6199f610576d2e11c03bec5f0 ]

RDS currently doesn't check if the length of the control message is large enough to hold the required data, before dereferencing the control message data. This results in following crash:

BUG: KASAN: stack-out-of-bounds in rds_rdma_bytes net/rds/send.c:1013
[inline]
BUG: KASAN: stack-out-of-bounds in rds_sendmsg+0x1f02/0x1f90
net/rds/send.c:1066
Read of size 8 at addr ffff8801c928fb70 by task syzkaller455006/3157

CPU: 0 PID: 3157 Comm: syzkaller455006 Not tainted 4.15.0-rc3+ #161
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 rds_rdma_bytes net/rds/send.c:1013 [inline]
 rds_sendmsg+0x1f02/0x1f90 net/rds/send.c:1066
 sock_sendmsg_nosec net/socket.c:628 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:638
 ___sys_sendmsg+0x320/0x8b0 net/socket.c:2018
 __sys_sendmmsg+0x1ee/0x620 net/socket.c:2108
 SYSC_sendmmsg net/socket.c:2139 [inline]
 SyS_sendmmsg+0x35/0x60 net/socket.c:2134
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x43fe49
RSP: 002b:00007fffbe244ad8 EFLAGS: 00000217 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fe49
RDX: 0000000000000001 RSI: 000000002020c000 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004017b0
R13: 0000000000401840 R14: 0000000000000000 R15: 0000000000000000

To fix this, we verify that the cmsg_len is large enough to hold the data to be read, before proceeding further.

---
 net/rds/send.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -1006,6 +1006,9 @@ static int rds_rdma_bytes(struct msghdr
 			continue;
 
 		if (cmsg->cmsg_type == RDS_CMSG_RDMA_ARGS) {
+			if (cmsg->cmsg_len <
+			    CMSG_LEN(sizeof(struct rds_rdma_args)))
+				return -EINVAL;
 			args = CMSG_DATA(cmsg);
 			*rdma_bytes += args->remote_vec.bytes;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/rds-check-cmsg_len-before-dereferencing-cmsg_data.patch