[PATCH net-next 01/10] net: annotate races around sk->sk_bound_dev_if

[Eric Dumazet]

From: Eric Dumazet <edum...@google.com>

UDP sendmsg() is lockless, and reads sk->sk_bound_dev_if while
this field can be changed by another thread.

Adds minimal annotations to avoid KCSAN splats for UDP.
Following patches will add more annotations to potential lockless readers.

BUG: KCSAN: data-race in __ip6_datagram_connect / udpv6_sendmsg

write to 0xffff888136d47a94 of 4 bytes by task 7681 on cpu 0:
__ip6_datagram_connect+0x6e2/0x930 net/ipv6/datagram.c:221
ip6_datagram_connect+0x2a/0x40 net/ipv6/datagram.c:272
inet_dgram_connect+0x107/0x190 net/ipv4/af_inet.c:576
__sys_connect_file net/socket.c:1900 [inline]
__sys_connect+0x197/0x1b0 net/socket.c:1917
__do_sys_connect net/socket.c:1927 [inline]
__se_sys_connect net/socket.c:1924 [inline]
__x64_sys_connect+0x3d/0x50 net/socket.c:1924
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888136d47a94 of 4 bytes by task 7670 on cpu 1:
udpv6_sendmsg+0xc60/0x16e0 net/ipv6/udp.c:1436
inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:652
sock_sendmsg_nosec net/socket.c:705 [inline]
sock_sendmsg net/socket.c:725 [inline]
____sys_sendmsg+0x39a/0x510 net/socket.c:2413
___sys_sendmsg net/socket.c:2467 [inline]
__sys_sendmmsg+0x267/0x4c0 net/socket.c:2553
__do_sys_sendmmsg net/socket.c:2582 [inline]
__se_sys_sendmmsg net/socket.c:2579 [inline]
__x64_sys_sendmmsg+0x53/0x60 net/socket.c:2579
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0xffffff9b

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7670 Comm: syz-executor.3 Tainted: G W 5.18.0-rc1-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

I chose to not add Fixes: tag because race has minor consequences
and stable teams busy enough.

Signed-off-by: Eric Dumazet <edum...@google.com>
Reported-by: syzbot <syzk...@googlegroups.com>
---
include/net/ip.h | 2 +-
include/net/sock.h | 5 +++--
net/ipv6/datagram.c | 6 +++---
net/ipv6/udp.c | 11 ++++++-----
4 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/include/net/ip.h b/include/net/ip.h
index 3984f2c39c4ba8b4d2a4e4dab6d743f0c9faf798..8ad04f60b4132e163381b3a051c3f3d13e57c2ba 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -93,7 +93,7 @@ static inline void ipcm_init_sk(struct ipcm_cookie *ipcm,

ipcm->sockc.mark = inet->sk.sk_mark;
ipcm->sockc.tsflags = inet->sk.sk_tsflags;
- ipcm->oif = inet->sk.sk_bound_dev_if;
+ ipcm->oif = READ_ONCE(inet->sk.sk_bound_dev_if);
ipcm->addr = inet->inet_saddr;
}

diff --git a/include/net/sock.h b/include/net/sock.h
index 73063c88a2499b31c1e8d25dc157d21f93b02bf5..f6663e1d881d16014cc1439f7bb04f5d16b3db4f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2878,13 +2878,14 @@ static inline void sk_pacing_shift_update(struct sock *sk, int val)
*/
static inline bool sk_dev_equal_l3scope(struct sock *sk, int dif)
{
+ int bound_dev_if = READ_ONCE(sk->sk_bound_dev_if);
int mdif;

- if (!sk->sk_bound_dev_if || sk->sk_bound_dev_if == dif)
+ if (!bound_dev_if || bound_dev_if == dif)
return true;

mdif = l3mdev_master_ifindex_by_index(sock_net(sk), dif);
- if (mdif && mdif == sk->sk_bound_dev_if)
+ if (mdif && mdif == bound_dev_if)
return true;

return false;
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 39b2327edc4e993d5a74a03eae8986a9152dea2b..df665d4e8f0f130f1d65e368f1b495fed794b70a 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -218,11 +218,11 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
err = -EINVAL;
goto out;
}
- sk->sk_bound_dev_if = usin->sin6_scope_id;
+ WRITE_ONCE(sk->sk_bound_dev_if, usin->sin6_scope_id);
}

if (!sk->sk_bound_dev_if && (addr_type & IPV6_ADDR_MULTICAST))
- sk->sk_bound_dev_if = np->mcast_oif;
+ WRITE_ONCE(sk->sk_bound_dev_if, np->mcast_oif);

/* Connect to link-local address requires an interface */
if (!sk->sk_bound_dev_if) {
@@ -798,7 +798,7 @@ int ip6_datagram_send_ctl(struct net *net, struct sock *sk,
if (src_idx) {
if (fl6->flowi6_oif &&
src_idx != fl6->flowi6_oif &&
- (sk->sk_bound_dev_if != fl6->flowi6_oif ||
+ (READ_ONCE(sk->sk_bound_dev_if) != fl6->flowi6_oif ||
!sk_dev_equal_l3scope(sk, src_idx)))
return -EINVAL;
fl6->flowi6_oif = src_idx;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3fc97d4621ac4a1f86de1f20375b33afffd0a2e6..960cfea820160614f3606ce4f407b7aa89fc70e1 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -105,7 +105,7 @@ static int compute_score(struct sock *sk, struct net *net,
const struct in6_addr *daddr, unsigned short hnum,
int dif, int sdif)
{
- int score;
+ int bound_dev_if, score;
struct inet_sock *inet;
bool dev_match;

@@ -132,10 +132,11 @@ static int compute_score(struct sock *sk, struct net *net,
score++;
}

- dev_match = udp_sk_bound_dev_eq(net, sk->sk_bound_dev_if, dif, sdif);
+ bound_dev_if = READ_ONCE(sk->sk_bound_dev_if);
+ dev_match = udp_sk_bound_dev_eq(net, bound_dev_if, dif, sdif);
if (!dev_match)
return -1;
- if (sk->sk_bound_dev_if)
+ if (bound_dev_if)
score++;

if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
@@ -789,7 +790,7 @@ static bool __udp_v6_is_mcast_sock(struct net *net, struct sock *sk,
(inet->inet_dport && inet->inet_dport != rmt_port) ||
(!ipv6_addr_any(&sk->sk_v6_daddr) &&
!ipv6_addr_equal(&sk->sk_v6_daddr, rmt_addr)) ||
- !udp_sk_bound_dev_eq(net, sk->sk_bound_dev_if, dif, sdif) ||
+ !udp_sk_bound_dev_eq(net, READ_ONCE(sk->sk_bound_dev_if), dif, sdif) ||
(!ipv6_addr_any(&sk->sk_v6_rcv_saddr) &&
!ipv6_addr_equal(&sk->sk_v6_rcv_saddr, loc_addr)))
return false;
@@ -1433,7 +1434,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
}

if (!fl6->flowi6_oif)
- fl6->flowi6_oif = sk->sk_bound_dev_if;
+ fl6->flowi6_oif = READ_ONCE(sk->sk_bound_dev_if);

if (!fl6->flowi6_oif)
fl6->flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
--
2.36.0.512.ge40c2bad7a-goog

[Eric Dumazet]

index 01edfde4257d697f2a2c88ef704a3849af4e5305..72ca97ccb46072491179c1225f4e8bab85a7994f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2875,13 +2875,14 @@ static inline void sk_pacing_shift_update(struct sock *sk, int val)

2.36.0.550.gb090851708-goog