Commit a1865f2e authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

netlink: annotate lockless accesses to nlk->max_recvmsg_len 



syzbot reported a data-race in data-race in netlink_recvmsg() [1]

Indeed, netlink_recvmsg() can be run concurrently,
and netlink_dump() also needs protection.

[1]
BUG: KCSAN: data-race in netlink_recvmsg / netlink_recvmsg

read to 0xffff888141840b38 of 8 bytes by task 23057 on cpu 0:
netlink_recvmsg+0xea/0x730 net/netlink/af_netlink.c:1988
sock_recvmsg_nosec net/socket.c:1017 [inline]
sock_recvmsg net/socket.c:1038 [inline]
__sys_recvfrom+0x1ee/0x2e0 net/socket.c:2194
__do_sys_recvfrom net/socket.c:2212 [inline]
__se_sys_recvfrom net/socket.c:2208 [inline]
__x64_sys_recvfrom+0x78/0x90 net/socket.c:2208
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

write to 0xffff888141840b38 of 8 bytes by task 23037 on cpu 1:
netlink_recvmsg+0x114/0x730 net/netlink/af_netlink.c:1989
sock_recvmsg_nosec net/socket.c:1017 [inline]
sock_recvmsg net/socket.c:1038 [inline]
____sys_recvmsg+0x156/0x310 net/socket.c:2720
___sys_recvmsg net/socket.c:2762 [inline]
do_recvmmsg+0x2e5/0x710 net/socket.c:2856
__sys_recvmmsg net/socket.c:2935 [inline]
__do_sys_recvmmsg net/socket.c:2958 [inline]
__se_sys_recvmmsg net/socket.c:2951 [inline]
__x64_sys_recvmmsg+0xe2/0x160 net/socket.c:2951
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0x0000000000001000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 23037 Comm: syz-executor.2 Not tainted 6.3.0-rc4-syzkaller-00195-g5a57b48fdfcb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023

Fixes: 9063e21f ("netlink: autosize skb lengthes")
Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarSimon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230403214643.768555-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent e847c767

net/netlink/af_netlink.c

+9 −6
Original line number Diff line number Diff line
@@ -1952,7 +1952,7 @@ static int netlink_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, 
	struct scm_cookie scm;

	struct sock *sk = sock->sk;

	struct netlink_sock *nlk = nlk_sk(sk);

	size_t copied;

	size_t copied, max_recvmsg_len;

	struct sk_buff *skb, *data_skb;

	int err, ret;
@@ -1985,9 +1985,10 @@ static int netlink_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, 
#endif



	/* Record the max length of recvmsg() calls for future allocations */

	nlk->max_recvmsg_len = max(nlk->max_recvmsg_len, len);

	nlk->max_recvmsg_len = min_t(size_t, nlk->max_recvmsg_len,

	max_recvmsg_len = max(READ_ONCE(nlk->max_recvmsg_len), len);

	max_recvmsg_len = min_t(size_t, max_recvmsg_len,

				SKB_WITH_OVERHEAD(32768));

	WRITE_ONCE(nlk->max_recvmsg_len, max_recvmsg_len);



	copied = data_skb->len;

	if (len < copied) {
@@ -2236,6 +2237,7 @@ static int netlink_dump(struct sock *sk) 
	struct netlink_ext_ack extack = {};

	struct netlink_callback *cb;

	struct sk_buff *skb = NULL;

	size_t max_recvmsg_len;

	struct module *module;

	int err = -ENOBUFS;

	int alloc_min_size;
@@ -2258,8 +2260,9 @@ static int netlink_dump(struct sock *sk) 
	cb = &nlk->cb;

	alloc_min_size = max_t(int, cb->min_dump_alloc, NLMSG_GOODSIZE);



	if (alloc_min_size < nlk->max_recvmsg_len) {

		alloc_size = nlk->max_recvmsg_len;

	max_recvmsg_len = READ_ONCE(nlk->max_recvmsg_len);

	if (alloc_min_size < max_recvmsg_len) {

		alloc_size = max_recvmsg_len;

		skb = alloc_skb(alloc_size,

				(GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) |

				__GFP_NOWARN | __GFP_NORETRY);