CVE-2026-53260

published 2026-06-25

CVE-2026-53260: In the Linux kernel, the following vulnerability has been resolved: tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req(). syzbot reported a…

Priority P3 52 critical 9.8 CVSS 3.1

AV N AC L PR N UI N S U C H I H A H

In the Linux kernel, the following vulnerability has been resolved:

tcp: Add preempt_{disable,enable}_nested() in reqsk_queue_hash_req().

syzbot reported a weird reqsk->rsk_refcnt underflow in
__inet_csk_reqsk_queue_drop().

The captured reqsk_put() in __inet_csk_reqsk_queue_drop()
is called only when it successfully removes reqsk from ehash.

Moreover, reqsk_timer_handler() calls another reqsk_put()
after that.

This indicates that the reqsk was missing both refcnts for
ehash and the timer itself.

Since all the syzbot reports had PREEMPT_RT enabled, the only
possible scenario is that reqsk_queue_hash_req() is preempted
after mod_timer() and before refcount_set(), and then the timer
triggered after 1s aborts the reqsk due to its listener's close().

Let's wrap mod_timer() and refcount_set() with
preempt_disable_nested() and preempt_enable_nested().

Note that inet_ehash_insert() holds the normal spin_lock()
(mutex in PREEMPT_RT), so it must be called outside of
preempt_disable_nested(), but this is fine.

The lookup path just ignores 0 sk_refcnt entries in ehash
and tries to create another reqsk, but this will fail at
inet_ehash_insert().

[0]:
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: ktimers/0/16
Modules linked in:
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: e4 7d d1 0a 67 48 0f b9 3a eb 4a e8 38 3d 23 fd 48 8d 3d e1 7d d1 0a 67 48 0f b9 3a eb 37 e8 25 3d 23 fd 48 8d 3d de 7d d1 0a 48 0f b9 3a eb 24 e8 12 3d 23 fd 48 8d 3d db 7d d1 0a 67 48 0f
RSP: 0000:ffffc90000157948 EFLAGS: 00010246
RAX: ffffffff84a1301b RBX: 0000000000000003 RCX: ffff88801ca98000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffffffff8f72ae00
RBP: ffffffff99ae3b01 R08: ffff88801ca9800

Affected

11 ranges

Vendor	Product	Version range	Fixed in
linux	linux	—	—
linux	linux	>= d2d6422f8bd17c6bb205133e290625a564194496 < b183215ff714efb747d9d5a429322ba6404b5401	b183215ff714efb747d9d5a429322ba6404b5401
linux	linux	>= d2d6422f8bd17c6bb205133e290625a564194496 < e10902df24488ca722303133acfc82490f7d59ad	e10902df24488ca722303133acfc82490f7d59ad
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	—	—
linux	linux_kernel	>= 6.12 < 7.0.13	7.0.13

CVSS provenance

nvd v3.1 9.8 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

vendor_redhat 9.8 CRITICAL

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