[PATCH v1 net] smc: Fix lockdep false-positive for IPPROTO_SMC.

[PATCH v1 net] smc: Fix lockdep false-positive for IPPROTO_SMC.

[Kuniyuki Iwashima]

SMC consists of two sockets: smc_sock and kernel TCP socket.

Currently, there are two ways of creating the sockets, and syzbot reported
a lockdep splat [0] for the newer way introduced by commit d25a92ccae6b
("net/smc: Introduce IPPROTO_SMC").

  socket(AF_SMC             , SOCK_STREAM, SMCPROTO_SMC or SMCPROTO_SMC6)
  socket(AF_INET or AF_INET6, SOCK_STREAM, IPPROTO_SMC)

When a socket is allocated, sock_lock_init() sets a lockdep lock class to
sk->sk_lock.slock based on its protocol family.  In the IPPROTO_SMC case,
AF_INET or AF_INET6 lock class is assigned to smc_sock.

The repro sets IPV6_JOIN_ANYCAST for IPv6 UDP and SMC socket and exercises
smc_switch_to_fallback() for IPPROTO_SMC.

  1. smc_switch_to_fallback() is called under lock_sock() and holds
     smc->clcsock_release_lock.

      sk_lock-AF_INET6 -> &smc->clcsock_release_lock
      (sk_lock-AF_SMC)

  2. Setting IPV6_JOIN_ANYCAST to SMC holds smc->clcsock_release_lock
     and calls setsockopt() for the kernel TCP socket, which holds RTNL
     and the kernel socket's lock_sock().

      &smc->clcsock_release_lock -> rtnl_mutex (-> k-sk_lock-AF_INET6)

  3. Setting IPV6_JOIN_ANYCAST to UDP holds RTNL and lock_sock().

      rtnl_mutex -> sk_lock-AF_INET6

Then, lockdep detects a false-positive circular locking,

  .-> sk_lock-AF_INET6 -> &smc->clcsock_release_lock -> rtnl_mutex -.
  `-----------------------------------------------------------------'

but IPPROTO_SMC should have the same locking rule as AF_SMC.

      sk_lock-AF_SMC   -> &smc->clcsock_release_lock -> rtnl_mutex -> k-sk_lock-AF_INET6

Let's set the same lock class for smc_sock.

Given AF_SMC uses the same lock class for SMCPROTO_SMC and SMCPROTO_SMC6,
we do not need to separate the class for AF_INET and AF_INET6.

[0]:
WARNING: possible circular locking dependency detected
6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0 Not tainted

syz.4.1528/11571 is trying to acquire lock:
ffffffff8fef8de8 (rtnl_mutex){+.+.}-{4:4}, at: ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220

but task is already holding lock:
ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

 -> #2 (&smc->clcsock_release_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
       smc_switch_to_fallback+0x2d/0xa00 net/smc/af_smc.c:903
       smc_sendmsg+0x13d/0x520 net/smc/af_smc.c:2781
       sock_sendmsg_nosec net/socket.c:718 [inline]
       __sock_sendmsg net/socket.c:733 [inline]
       ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2573
       ___sys_sendmsg+0x135/0x1e0 net/socket.c:2627
       __sys_sendmsg+0x16e/0x220 net/socket.c:2659
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

 -> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0x3a/0xf0 net/core/sock.c:3645
       lock_sock include/net/sock.h:1624 [inline]
       sockopt_lock_sock net/core/sock.c:1133 [inline]
       sockopt_lock_sock+0x54/0x70 net/core/sock.c:1124
       do_ipv6_setsockopt+0x2160/0x4520 net/ipv6/ipv6_sockglue.c:567
       ipv6_setsockopt+0xcb/0x170 net/ipv6/ipv6_sockglue.c:993
       udpv6_setsockopt+0x7d/0xd0 net/ipv6/udp.c:1850
       do_sock_setsockopt+0x222/0x480 net/socket.c:2303
       __sys_setsockopt+0x1a0/0x230 net/socket.c:2328
       __do_sys_setsockopt net/socket.c:2334 [inline]
       __se_sys_setsockopt net/socket.c:2331 [inline]
       __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2331
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

 -> #0 (rtnl_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3163 [inline]
       check_prevs_add kernel/locking/lockdep.c:3282 [inline]
       validate_chain kernel/locking/lockdep.c:3906 [inline]
       __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
       lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
       ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
       inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
       __sock_release net/socket.c:647 [inline]
       sock_release+0x8e/0x1d0 net/socket.c:675
       smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
       __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
       smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
       __sock_release+0xb0/0x270 net/socket.c:647
       sock_close+0x1c/0x30 net/socket.c:1398
       __fput+0x3ff/0xb70 fs/file_table.c:464
       task_work_run+0x14e/0x250 kernel/task_work.c:227
       resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
       exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
       __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
       syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
       do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  rtnl_mutex --> sk_lock-AF_INET6 --> &smc->clcsock_release_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&smc->clcsock_release_lock);
                               lock(sk_lock-AF_INET6);
                               lock(&smc->clcsock_release_lock);
  lock(rtnl_mutex);

 *** DEADLOCK ***

2 locks held by syz.4.1528/11571:
 #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
 #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: __sock_release+0x86/0x270 net/socket.c:646
 #1: ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30

stack backtrace:
CPU: 0 UID: 0 PID: 11571 Comm: syz.4.1528 Not tainted 6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208
 check_prev_add kernel/locking/lockdep.c:3163 [inline]
 check_prevs_add kernel/locking/lockdep.c:3282 [inline]
 validate_chain kernel/locking/lockdep.c:3906 [inline]
 __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
 lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
 __mutex_lock_common kernel/locking/mutex.c:585 [inline]
 __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
 ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
 inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
 __sock_release net/socket.c:647 [inline]
 sock_release+0x8e/0x1d0 net/socket.c:675
 smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
 __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
 smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
 __sock_release+0xb0/0x270 net/socket.c:647
 sock_close+0x1c/0x30 net/socket.c:1398
 __fput+0x3ff/0xb70 fs/file_table.c:464
 task_work_run+0x14e/0x250 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
 do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8b4b38d169
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:00007ffe4efd22d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00000000000b14a3 RCX: 00007f8b4b38d169
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f8b4b5a7ba0 R08: 0000000000000001 R09: 000000114efd25cf
R10: 00007f8b4b200000 R11: 0000000000000246 R12: 00007f8b4b5a5fac
R13: 00007f8b4b5a5fa0 R14: ffffffffffffffff R15: 00007ffe4efd23f0
 </TASK>

Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
Reported-by: syzbot+be6f4b383534d88989f7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=be6f4b383534d88989f7
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/smc/af_smc.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 3e6cb35baf25..3760131f1484 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -362,6 +362,9 @@ static void smc_destruct(struct sock *sk)
 		return;
 }
 
+static struct lock_class_key smc_key;
+static struct lock_class_key smc_slock_key;
+
 void smc_sk_init(struct net *net, struct sock *sk, int protocol)
 {
 	struct smc_sock *smc = smc_sk(sk);
@@ -375,6 +378,8 @@ void smc_sk_init(struct net *net, struct sock *sk, int protocol)
 	INIT_WORK(&smc->connect_work, smc_connect_work);
 	INIT_DELAYED_WORK(&smc->conn.tx_work, smc_tx_work);
 	INIT_LIST_HEAD(&smc->accept_q);
+	sock_lock_init_class_and_name(sk, "slock-AF_SMC", &smc_slock_key,
+				      "sk_lock-AF_SMC", &smc_key);
 	spin_lock_init(&smc->accept_q_lock);
 	spin_lock_init(&smc->conn.send_lock);
 	sk->sk_prot->hash(sk);
-- 
2.48.1

Re: [PATCH v1 net] smc: Fix lockdep false-positive for IPPROTO_SMC.

[Paolo Abeni]

On 4/7/25 7:03 PM, Kuniyuki Iwashima wrote:
> SMC consists of two sockets: smc_sock and kernel TCP socket.
> 
> Currently, there are two ways of creating the sockets, and syzbot reported
> a lockdep splat [0] for the newer way introduced by commit d25a92ccae6b
> ("net/smc: Introduce IPPROTO_SMC").
> 
>   socket(AF_SMC             , SOCK_STREAM, SMCPROTO_SMC or SMCPROTO_SMC6)
>   socket(AF_INET or AF_INET6, SOCK_STREAM, IPPROTO_SMC)
> 
> When a socket is allocated, sock_lock_init() sets a lockdep lock class to
> sk->sk_lock.slock based on its protocol family.  In the IPPROTO_SMC case,
> AF_INET or AF_INET6 lock class is assigned to smc_sock.
> 
> The repro sets IPV6_JOIN_ANYCAST for IPv6 UDP and SMC socket and exercises
> smc_switch_to_fallback() for IPPROTO_SMC.
> 
>   1. smc_switch_to_fallback() is called under lock_sock() and holds
>      smc->clcsock_release_lock.
> 
>       sk_lock-AF_INET6 -> &smc->clcsock_release_lock
>       (sk_lock-AF_SMC)
> 
>   2. Setting IPV6_JOIN_ANYCAST to SMC holds smc->clcsock_release_lock
>      and calls setsockopt() for the kernel TCP socket, which holds RTNL
>      and the kernel socket's lock_sock().
> 
>       &smc->clcsock_release_lock -> rtnl_mutex (-> k-sk_lock-AF_INET6)
> 
>   3. Setting IPV6_JOIN_ANYCAST to UDP holds RTNL and lock_sock().
> 
>       rtnl_mutex -> sk_lock-AF_INET6
> 
> Then, lockdep detects a false-positive circular locking,
> 
>   .-> sk_lock-AF_INET6 -> &smc->clcsock_release_lock -> rtnl_mutex -.
>   `-----------------------------------------------------------------'
> 
> but IPPROTO_SMC should have the same locking rule as AF_SMC.
> 
>       sk_lock-AF_SMC   -> &smc->clcsock_release_lock -> rtnl_mutex -> k-sk_lock-AF_INET6
> 
> Let's set the same lock class for smc_sock.
> 
> Given AF_SMC uses the same lock class for SMCPROTO_SMC and SMCPROTO_SMC6,
> we do not need to separate the class for AF_INET and AF_INET6.
> 
> [0]:
> WARNING: possible circular locking dependency detected
> 6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0 Not tainted
> 
> syz.4.1528/11571 is trying to acquire lock:
> ffffffff8fef8de8 (rtnl_mutex){+.+.}-{4:4}, at: ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
> 
> but task is already holding lock:
> ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
>  -> #2 (&smc->clcsock_release_lock){+.+.}-{4:4}:
>        __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>        __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>        smc_switch_to_fallback+0x2d/0xa00 net/smc/af_smc.c:903
>        smc_sendmsg+0x13d/0x520 net/smc/af_smc.c:2781
>        sock_sendmsg_nosec net/socket.c:718 [inline]
>        __sock_sendmsg net/socket.c:733 [inline]
>        ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2573
>        ___sys_sendmsg+0x135/0x1e0 net/socket.c:2627
>        __sys_sendmsg+0x16e/0x220 net/socket.c:2659
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>  -> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
>        lock_sock_nested+0x3a/0xf0 net/core/sock.c:3645
>        lock_sock include/net/sock.h:1624 [inline]
>        sockopt_lock_sock net/core/sock.c:1133 [inline]
>        sockopt_lock_sock+0x54/0x70 net/core/sock.c:1124
>        do_ipv6_setsockopt+0x2160/0x4520 net/ipv6/ipv6_sockglue.c:567
>        ipv6_setsockopt+0xcb/0x170 net/ipv6/ipv6_sockglue.c:993
>        udpv6_setsockopt+0x7d/0xd0 net/ipv6/udp.c:1850
>        do_sock_setsockopt+0x222/0x480 net/socket.c:2303
>        __sys_setsockopt+0x1a0/0x230 net/socket.c:2328
>        __do_sys_setsockopt net/socket.c:2334 [inline]
>        __se_sys_setsockopt net/socket.c:2331 [inline]
>        __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2331
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>  -> #0 (rtnl_mutex){+.+.}-{4:4}:
>        check_prev_add kernel/locking/lockdep.c:3163 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3282 [inline]
>        validate_chain kernel/locking/lockdep.c:3906 [inline]
>        __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
>        lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
>        __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>        __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>        ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
>        inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
>        __sock_release net/socket.c:647 [inline]
>        sock_release+0x8e/0x1d0 net/socket.c:675
>        smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
>        __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
>        smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
>        __sock_release+0xb0/0x270 net/socket.c:647
>        sock_close+0x1c/0x30 net/socket.c:1398
>        __fput+0x3ff/0xb70 fs/file_table.c:464
>        task_work_run+0x14e/0x250 kernel/task_work.c:227
>        resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>        exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>        exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
>        __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>        syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
>        do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   rtnl_mutex --> sk_lock-AF_INET6 --> &smc->clcsock_release_lock
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&smc->clcsock_release_lock);
>                                lock(sk_lock-AF_INET6);
>                                lock(&smc->clcsock_release_lock);
>   lock(rtnl_mutex);
> 
>  *** DEADLOCK ***
> 
> 2 locks held by syz.4.1528/11571:
>  #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
>  #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: __sock_release+0x86/0x270 net/socket.c:646
>  #1: ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30
> 
> stack backtrace:
> CPU: 0 UID: 0 PID: 11571 Comm: syz.4.1528 Not tainted 6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
>  print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076
>  check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208
>  check_prev_add kernel/locking/lockdep.c:3163 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3282 [inline]
>  validate_chain kernel/locking/lockdep.c:3906 [inline]
>  __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
>  lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
>  __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>  __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>  ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
>  inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
>  __sock_release net/socket.c:647 [inline]
>  sock_release+0x8e/0x1d0 net/socket.c:675
>  smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
>  __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
>  smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
>  __sock_release+0xb0/0x270 net/socket.c:647
>  sock_close+0x1c/0x30 net/socket.c:1398
>  __fput+0x3ff/0xb70 fs/file_table.c:464
>  task_work_run+0x14e/0x250 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>  exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>  syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
>  do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f8b4b38d169
> 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:00007ffe4efd22d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
> RAX: 0000000000000000 RBX: 00000000000b14a3 RCX: 00007f8b4b38d169
> RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
> RBP: 00007f8b4b5a7ba0 R08: 0000000000000001 R09: 000000114efd25cf
> R10: 00007f8b4b200000 R11: 0000000000000246 R12: 00007f8b4b5a5fac
> R13: 00007f8b4b5a5fa0 R14: ffffffffffffffff R15: 00007ffe4efd23f0
>  </TASK>
> 
> Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
> Reported-by: syzbot+be6f4b383534d88989f7@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=be6f4b383534d88989f7
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Makes sense to me, waiting a little more to allow feedback from @Wenjia
and the SMC crew.

Thanks,

Paolo

Re: [PATCH v1 net] smc: Fix lockdep false-positive for IPPROTO_SMC.

[Wenjia Zhang]

On 07.04.25 19:03, Kuniyuki Iwashima wrote:
> SMC consists of two sockets: smc_sock and kernel TCP socket.
> 
> Currently, there are two ways of creating the sockets, and syzbot reported
> a lockdep splat [0] for the newer way introduced by commit d25a92ccae6b
> ("net/smc: Introduce IPPROTO_SMC").
> 
>    socket(AF_SMC             , SOCK_STREAM, SMCPROTO_SMC or SMCPROTO_SMC6)
>    socket(AF_INET or AF_INET6, SOCK_STREAM, IPPROTO_SMC)
> 
> When a socket is allocated, sock_lock_init() sets a lockdep lock class to
> sk->sk_lock.slock based on its protocol family.  In the IPPROTO_SMC case,
> AF_INET or AF_INET6 lock class is assigned to smc_sock.
> 
> The repro sets IPV6_JOIN_ANYCAST for IPv6 UDP and SMC socket and exercises
> smc_switch_to_fallback() for IPPROTO_SMC.
> 
>    1. smc_switch_to_fallback() is called under lock_sock() and holds
>       smc->clcsock_release_lock.
> 
>        sk_lock-AF_INET6 -> &smc->clcsock_release_lock
>        (sk_lock-AF_SMC)
> 
>    2. Setting IPV6_JOIN_ANYCAST to SMC holds smc->clcsock_release_lock
>       and calls setsockopt() for the kernel TCP socket, which holds RTNL
>       and the kernel socket's lock_sock().
> 
>        &smc->clcsock_release_lock -> rtnl_mutex (-> k-sk_lock-AF_INET6)
> 
>    3. Setting IPV6_JOIN_ANYCAST to UDP holds RTNL and lock_sock().
> 
>        rtnl_mutex -> sk_lock-AF_INET6
> 
> Then, lockdep detects a false-positive circular locking,
> 
>    .-> sk_lock-AF_INET6 -> &smc->clcsock_release_lock -> rtnl_mutex -.
>    `-----------------------------------------------------------------'
> 
> but IPPROTO_SMC should have the same locking rule as AF_SMC.
> 
>        sk_lock-AF_SMC   -> &smc->clcsock_release_lock -> rtnl_mutex -> k-sk_lock-AF_INET6
> 
> Let's set the same lock class for smc_sock.
> 
> Given AF_SMC uses the same lock class for SMCPROTO_SMC and SMCPROTO_SMC6,
> we do not need to separate the class for AF_INET and AF_INET6.
> 
> [0]:
> WARNING: possible circular locking dependency detected
> 6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0 Not tainted
> 
> syz.4.1528/11571 is trying to acquire lock:
> ffffffff8fef8de8 (rtnl_mutex){+.+.}-{4:4}, at: ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
> 
> but task is already holding lock:
> ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
>   -> #2 (&smc->clcsock_release_lock){+.+.}-{4:4}:
>         __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>         __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>         smc_switch_to_fallback+0x2d/0xa00 net/smc/af_smc.c:903
>         smc_sendmsg+0x13d/0x520 net/smc/af_smc.c:2781
>         sock_sendmsg_nosec net/socket.c:718 [inline]
>         __sock_sendmsg net/socket.c:733 [inline]
>         ____sys_sendmsg+0xaaf/0xc90 net/socket.c:2573
>         ___sys_sendmsg+0x135/0x1e0 net/socket.c:2627
>         __sys_sendmsg+0x16e/0x220 net/socket.c:2659
>         do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>         do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>         entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>   -> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
>         lock_sock_nested+0x3a/0xf0 net/core/sock.c:3645
>         lock_sock include/net/sock.h:1624 [inline]
>         sockopt_lock_sock net/core/sock.c:1133 [inline]
>         sockopt_lock_sock+0x54/0x70 net/core/sock.c:1124
>         do_ipv6_setsockopt+0x2160/0x4520 net/ipv6/ipv6_sockglue.c:567
>         ipv6_setsockopt+0xcb/0x170 net/ipv6/ipv6_sockglue.c:993
>         udpv6_setsockopt+0x7d/0xd0 net/ipv6/udp.c:1850
>         do_sock_setsockopt+0x222/0x480 net/socket.c:2303
>         __sys_setsockopt+0x1a0/0x230 net/socket.c:2328
>         __do_sys_setsockopt net/socket.c:2334 [inline]
>         __se_sys_setsockopt net/socket.c:2331 [inline]
>         __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2331
>         do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>         do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>         entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
>   -> #0 (rtnl_mutex){+.+.}-{4:4}:
>         check_prev_add kernel/locking/lockdep.c:3163 [inline]
>         check_prevs_add kernel/locking/lockdep.c:3282 [inline]
>         validate_chain kernel/locking/lockdep.c:3906 [inline]
>         __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
>         lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
>         __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>         __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>         ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
>         inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
>         __sock_release net/socket.c:647 [inline]
>         sock_release+0x8e/0x1d0 net/socket.c:675
>         smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
>         __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
>         smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
>         __sock_release+0xb0/0x270 net/socket.c:647
>         sock_close+0x1c/0x30 net/socket.c:1398
>         __fput+0x3ff/0xb70 fs/file_table.c:464
>         task_work_run+0x14e/0x250 kernel/task_work.c:227
>         resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>         exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>         exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
>         __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>         syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
>         do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
>         entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> other info that might help us debug this:
> 
> Chain exists of:
>    rtnl_mutex --> sk_lock-AF_INET6 --> &smc->clcsock_release_lock
> 
>   Possible unsafe locking scenario:
> 
>         CPU0                    CPU1
>         ----                    ----
>    lock(&smc->clcsock_release_lock);
>                                 lock(sk_lock-AF_INET6);
>                                 lock(&smc->clcsock_release_lock);
>    lock(rtnl_mutex);
> 
>   *** DEADLOCK ***
> 
> 2 locks held by syz.4.1528/11571:
>   #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
>   #0: ffff888077e88208 (&sb->s_type->i_mutex_key#10){+.+.}-{4:4}, at: __sock_release+0x86/0x270 net/socket.c:646
>   #1: ffff888027f596a8 (&smc->clcsock_release_lock){+.+.}-{4:4}, at: smc_clcsock_release+0x75/0xe0 net/smc/smc_close.c:30
> 
> stack backtrace:
> CPU: 0 UID: 0 PID: 11571 Comm: syz.4.1528 Not tainted 6.14.0-rc3-syzkaller-00267-gff202c5028a1 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
>   print_circular_bug+0x490/0x760 kernel/locking/lockdep.c:2076
>   check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2208
>   check_prev_add kernel/locking/lockdep.c:3163 [inline]
>   check_prevs_add kernel/locking/lockdep.c:3282 [inline]
>   validate_chain kernel/locking/lockdep.c:3906 [inline]
>   __lock_acquire+0x249e/0x3c40 kernel/locking/lockdep.c:5228
>   lock_acquire.part.0+0x11b/0x380 kernel/locking/lockdep.c:5851
>   __mutex_lock_common kernel/locking/mutex.c:585 [inline]
>   __mutex_lock+0x19b/0xb10 kernel/locking/mutex.c:730
>   ipv6_sock_ac_close+0xd9/0x110 net/ipv6/anycast.c:220
>   inet6_release+0x47/0x70 net/ipv6/af_inet6.c:485
>   __sock_release net/socket.c:647 [inline]
>   sock_release+0x8e/0x1d0 net/socket.c:675
>   smc_clcsock_release+0xb7/0xe0 net/smc/smc_close.c:34
>   __smc_release+0x5c2/0x880 net/smc/af_smc.c:301
>   smc_release+0x1fc/0x5f0 net/smc/af_smc.c:344
>   __sock_release+0xb0/0x270 net/socket.c:647
>   sock_close+0x1c/0x30 net/socket.c:1398
>   __fput+0x3ff/0xb70 fs/file_table.c:464
>   task_work_run+0x14e/0x250 kernel/task_work.c:227
>   resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>   exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>   exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
>   __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>   syscall_exit_to_user_mode+0x27b/0x2a0 kernel/entry/common.c:218
>   do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f8b4b38d169
> 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:00007ffe4efd22d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
> RAX: 0000000000000000 RBX: 00000000000b14a3 RCX: 00007f8b4b38d169
> RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
> RBP: 00007f8b4b5a7ba0 R08: 0000000000000001 R09: 000000114efd25cf
> R10: 00007f8b4b200000 R11: 0000000000000246 R12: 00007f8b4b5a5fac
> R13: 00007f8b4b5a5fa0 R14: ffffffffffffffff R15: 00007ffe4efd23f0
>   </TASK>
> 
> Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
> Reported-by: syzbot+be6f4b383534d88989f7@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=be6f4b383534d88989f7
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thank you for fixing it! It looks reasonable to me! Good description!

Reviewed-by: Wenjia Zhang <wenjia@linux.ibm.com>

Re: [PATCH v1 net] smc: Fix lockdep false-positive for IPPROTO_SMC.

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 7 Apr 2025 10:03:17 -0700 you wrote:
> SMC consists of two sockets: smc_sock and kernel TCP socket.
> 
> Currently, there are two ways of creating the sockets, and syzbot reported
> a lockdep splat [0] for the newer way introduced by commit d25a92ccae6b
> ("net/smc: Introduce IPPROTO_SMC").
> 
>   socket(AF_SMC             , SOCK_STREAM, SMCPROTO_SMC or SMCPROTO_SMC6)
>   socket(AF_INET or AF_INET6, SOCK_STREAM, IPPROTO_SMC)
> 
> [...]

Here is the summary with links:
  - [v1,net] smc: Fix lockdep false-positive for IPPROTO_SMC.
    https://git.kernel.org/netdev/net/c/752e2217d789

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
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