From 14e138a86f6347c6199f610576d2e11c03bec5f0 Mon Sep 17 00:00:00 2001 From: Avinash Repaka Date: Thu, 21 Dec 2017 20:17:04 -0800 Subject: [PATCH] RDS: Check cmsg_len before dereferencing CMSG_DATA 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. Reported-by: syzbot Signed-off-by: Avinash Repaka Acked-by: Santosh Shilimkar Reviewed-by: Yuval Shaia Signed-off-by: David S. Miller --- net/rds/send.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/rds/send.c b/net/rds/send.c index b52cdc8ae428..f72466c63f0c 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -1009,6 +1009,9 @@ static int rds_rdma_bytes(struct msghdr *msg, size_t *rdma_bytes) 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; }