CVE: CVE-2024-39500
Published: 2024-07-12
Description: In the Linux kernel, the following vulnerability has been resolved:

sock_map: avoid race between sock_map_close and sk_psock_put

sk_psock_get will return NULL if the refcount of psock has gone to 0, which
will happen when the last call of sk_psock_put is done. However,
sk_psock_drop may not have finished yet, so the close callback will still
point to sock_map_close despite psock being NULL.

This can be reproduced with a thread deleting an element from the sock map,
while the second one creates a socket, adds it to the map and closes it.

That will trigger the WARN_ON_ONCE:

------------[ cut here ]------------
WARNING: CPU: 1 PID: 7220 at net/core/sock_map.c:1701 sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701
Modules linked in:
CPU: 1 PID: 7220 Comm: syz-executor380 Not tainted 6.9.0-syzkaller-07726-g3c999d1ae3c7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
RIP: 0010:sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701
Code: df e8 92 29 88 f8 48 8b 1b 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 79 29 88 f8 4c 8b 23 eb 89 e8 4f 15 23 f8 90 <0f> 0b 90 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d e9 13 26 3d 02
RSP: 0018:ffffc9000441fda8 EFLAGS: 00010293
RAX: ffffffff89731ae1 RBX: ffffffff94b87540 RCX: ffff[PII_REDACTED]00
RDX: [PII_REDACTED] RSI: ffffffff8bcab5c0 RDI: ffffffff8c1faba0
RBP: [PII_REDACTED] R08: ffffffff92f9b61f R09: 1ffffffff25f36c3
R10: dffffc[PII_REDACTED] R11: fffffbfff25f36c4 R12: ffffffff89731840
R13: ffff88804b587000 R14: ffff88804b587000 R15: ffffffff89731870
FS:  000055555e080380(0000) GS:ffff8880b9500000(0000) knlGS:[PII_REDACTED]
CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2: [PII_REDACTED] CR3:[PII_REDACTED]7d4000 CR4:[PII_REDACTED]350ef0
Call Trace:
 <TASK>
 unix_release+0x87/0xc0 net/unix/af_unix.c:1048
 __sock_release net/socket.c:659 [inline]
 sock_close+0xbe/0x240 net/socket.c:1421
 __fput+0x42b/0x8a0 fs/file_table.c:422
 __do_sys_close fs/open.c:1556 [inline]
 __se_sys_close fs/open.c:1541 [inline]
 __x64_sys_close+0x7f/0x110 fs/open.c:1541
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb37d618070
Code: 00 00 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff eb d4 e8 10 2c 00 00 80 3d 31 f0 07 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
RSP: 002b:00007ffcd4a525d8 EFLAGS: 00000202 ORIG_RAX: [PII_REDACTED]
RAX: ffffffffffffffda RBX: [PII_REDACTED] RCX: 00007fb37d618070
RDX: [PII_REDACTED] RSI:[PII_REDACTED]0001c0 RDI: [PII_REDACTED]
RBP: [PII_REDACTED] R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: [PII_REDACTED]
R13: [PII_REDACTED] R14: [PII_REDACTED] R15: [PII_REDACTED]
 </TASK>

Use sk_psock, which will only check that the pointer is not been set to
NULL yet, which should only happen after the callbacks are restored. If,
then, a reference can still be gotten, we may call sk_psock_stop and cancel
psock->work.

As suggested by Paolo Abeni, reorder the condition so the control flow is
less convoluted.

After that change, the reproducer does not trigger the WARN_ON_ONCE
anymore.
CVSS Score: 4.7 (MEDIUM)
CWE: CWE-362, CWE-617
References: https://git.kernel.org/stable/c/3627605de498639a3c586c8684d12c89cba11073; https://git.kernel.org/stable/c/4959ffc65a0e94f8acaac20deac49f89e6ded52d; https://git.kernel.org/stable/c/4b4647add7d3c8530493f7247d11e257ee425bf0