From: Kuniyuki Iwashima Date: Mon, 20 Apr 2026 19:48:41 +0000 (+0000) Subject: sockmap: Fix sk_psock_drop() race vs sock_map_{unhash,close,destroy}(). X-Git-Tag: v7.1-rc3~4^2~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6451d58a355642b612f2bf948ad39108c998ac2a;p=thirdparty%2Fkernel%2Flinux.git sockmap: Fix sk_psock_drop() race vs sock_map_{unhash,close,destroy}(). syzbot reported a splat in sock_map_destroy() [0], where psock was NULL even though sk->sk_prot still pointed to tcp_bpf_prots[][]. The stack trace shows how badly the path was excercised, see inet_release() calls tcp_close(), not sock_map_close() yet, but finally reaching sock_map_destroy(). The root cause is a lack of synchronisation. Even if sk_psock_get() fails to bump psock->refcnt, it does not guarantee that sk_psock_drop() has finished, and thus sk->sk_prot might not have been restored to the original one. Commit 4b4647add7d3 ("sock_map: avoid race between sock_map_close and sk_psock_put") attempted to address this, but it was insufficient for two reasons. It did not cover sock_map_unhash() and sock_map_destroy(), and it missed the corner case where sk_psock() is NULL. On non-x86 platforms, sk_psock_restore_proto(sk, psock) and rcu_assign_sk_user_data(sk, NULL) can be reordered because there is no address dependency between sk->sk_prot and sk->sk_user_data. sk_psock_get() returning NULL implies nothing about sk->sk_prot. Let's simply retry sk_psock_get() in the unlikely case. Note that we cannot avoid loop even if we added memory barrier in sk_psock_drop() and sock_map_psock_get_checked(). Also note that sock_map_destroy() cannot be called from softirq while sock_map_close() has also been running. It is because sock_map_destroy() requires SOCK_DEAD, so sock_map_destroy() cannot happen until sock_map_close() has finished the saved_close() (which is tcp_close()). [0]: WARNING: CPU: 1 PID: 8459 at net/core/sock_map.c:1667 sock_map_destroy+0x28b/0x2b0 net/core/sock_map.c:1667 Modules linked in: CPU: 1 UID: 0 PID: 8459 Comm: syz.0.1109 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:sock_map_destroy+0x28b/0x2b0 net/core/sock_map.c:1667 Code: 8b 36 49 83 c6 38 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 93 62 22 f9 4d 8b 3e e9 79 ff ff ff e8 a6 2b c3 f8 90 <0f> 0b 90 eb 9c e8 9b 2b c3 f8 4c 89 e7 be 03 00 00 00 e8 0e 4e bc RSP: 0018:ffffc9000d067be8 EFLAGS: 00010293 RAX: ffffffff88fb30aa RBX: ffff888024832000 RCX: ffff888024283b80 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000 R10: dffffc0000000000 R11: ffffed100862e946 R12: dffffc0000000000 R13: ffff888024832000 R14: ffffffff995b2208 R15: ffffffff88fb2e20 FS: 0000555579a7d500(0000) GS:ffff8881269c2000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00002000000048c0 CR3: 000000003713a000 CR4: 00000000003526f0 Call Trace: inet_csk_destroy_sock+0x166/0x3a0 net/ipv4/inet_connection_sock.c:1294 __tcp_close+0xcc1/0xfd0 net/ipv4/tcp.c:3262 tcp_close+0x28/0x110 net/ipv4/tcp.c:3274 inet_release+0x144/0x190 net/ipv4/af_inet.c:435 __sock_release net/socket.c:649 [inline] sock_close+0xc0/0x240 net/socket.c:1439 __fput+0x45b/0xa80 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0xec/0x110 kernel/entry/common.c:43 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline] do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f265847ebe9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffd158dfbd8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 000000000002ddb0 RCX: 00007f265847ebe9 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f26586a7da0 R08: 0000000000000001 R09: 0000000e158dfecf R10: 0000001b30a20000 R11: 0000000000000246 R12: 00007f26586a5fac R13: 00007f26586a5fa0 R14: ffffffffffffffff R15: 00007ffd158dfcf0 Fixes: 1aa12bdf1bfb ("bpf: sockmap, add sock close() hook to remove socks") Fixes: b05545e15e1f ("bpf: sockmap, fix transition through disconnect without close") Fixes: d8616ee2affc ("bpf, sockmap: Fix sk->sk_forward_alloc warn_on in sk_stream_kill_queues") Reported-by: syzbot+b0842d38af58376d1fdc@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/69cec5ef.050a0220.2dbe29.0009.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima Signed-off-by: Martin KaFai Lau Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20260420194846.1089595-1-kuniyu@google.com --- diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 02a68be3002a..99e3789492a0 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -1630,18 +1630,23 @@ void sock_map_unhash(struct sock *sk) void (*saved_unhash)(struct sock *sk); struct sk_psock *psock; +retry: rcu_read_lock(); psock = sk_psock(sk); if (unlikely(!psock)) { rcu_read_unlock(); saved_unhash = READ_ONCE(sk->sk_prot)->unhash; + if (unlikely(saved_unhash == sock_map_unhash)) + goto retry; } else { saved_unhash = psock->saved_unhash; sock_map_remove_links(sk, psock); rcu_read_unlock(); + + if (WARN_ON_ONCE(saved_unhash == sock_map_unhash)) + return; } - if (WARN_ON_ONCE(saved_unhash == sock_map_unhash)) - return; + if (saved_unhash) saved_unhash(sk); } @@ -1652,20 +1657,25 @@ void sock_map_destroy(struct sock *sk) void (*saved_destroy)(struct sock *sk); struct sk_psock *psock; +retry: rcu_read_lock(); psock = sk_psock_get(sk); if (unlikely(!psock)) { rcu_read_unlock(); saved_destroy = READ_ONCE(sk->sk_prot)->destroy; + if (unlikely(saved_destroy == sock_map_destroy)) + goto retry; } else { saved_destroy = psock->saved_destroy; sock_map_remove_links(sk, psock); rcu_read_unlock(); sk_psock_stop(psock); sk_psock_put(sk, psock); + + if (WARN_ON_ONCE(saved_destroy == sock_map_destroy)) + return; } - if (WARN_ON_ONCE(saved_destroy == sock_map_destroy)) - return; + if (saved_destroy) saved_destroy(sk); } @@ -1676,32 +1686,33 @@ void sock_map_close(struct sock *sk, long timeout) void (*saved_close)(struct sock *sk, long timeout); struct sk_psock *psock; +retry: lock_sock(sk); rcu_read_lock(); - psock = sk_psock(sk); + psock = sk_psock_get(sk); if (likely(psock)) { saved_close = psock->saved_close; sock_map_remove_links(sk, psock); - psock = sk_psock_get(sk); - if (unlikely(!psock)) - goto no_psock; rcu_read_unlock(); sk_psock_stop(psock); release_sock(sk); cancel_delayed_work_sync(&psock->work); sk_psock_put(sk, psock); + + /* Make sure we do not recurse. This is a bug. + * Leak the socket instead of crashing on a stack overflow. + */ + if (WARN_ON_ONCE(saved_close == sock_map_close)) + return; } else { saved_close = READ_ONCE(sk->sk_prot)->close; -no_psock: rcu_read_unlock(); release_sock(sk); + + if (unlikely(saved_close == sock_map_close)) + goto retry; } - /* Make sure we do not recurse. This is a bug. - * Leak the socket instead of crashing on a stack overflow. - */ - if (WARN_ON_ONCE(saved_close == sock_map_close)) - return; saved_close(sk, timeout); } EXPORT_SYMBOL_GPL(sock_map_close);