CVE-2026-89603: entry: Fix seccomp bypass after ptrace with TSYNC

CVE-2026-89603: entry: Fix seccomp bypass after ptrace with TSYNC

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

entry: Fix seccomp bypass after ptrace with TSYNC

Sashiko review pointed out the following issue.

If a thread is stopped in syscall_trace_enter() for ptrace, another
thread can install a seccomp filter with SECCOMP_FILTER_FLAG_TSYNC
(e.g., via seccomp_attach_filter()). This will successfully set
SYSCALL_WORK_SECCOMP on the stopped thread, but syscall_trace_enter()
evaluates a cached 'work' variable sampled on entry. Consequently,
the subsequent check for SYSCALL_WORK_SECCOMP misses the newly
assigned flag, and the filter is silently bypassed.

This race condition could allow an unprivileged process to execute
a prohibited system call (e.g., execve) that the newly installed filter
was intended to block, especially since the tracer might have modified
the system call number during the ptrace stop.

Fix this by re-reading the syscall_work flags after ptrace handling,
so that any new SYSCALL_WORK_SECCOMP flag set by another thread via
TSYNC during the ptrace stop is observed before the subsequent
seccomp check.

The Linux kernel CVE team has assigned CVE-2026-89603 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.9 with commit 142781e108b13b2b0e8f035cfb5bfbbc8f14d887 and fixed in 6.18.51 with commit 459f33f82864723a7fa366cf1091d9c6c893b6b2
	Issue introduced in 5.9 with commit 142781e108b13b2b0e8f035cfb5bfbbc8f14d887 and fixed in 7.2.4 with commit ab4647459098a43e9d6fdb860836f08c962f3774
	Issue introduced in 5.9 with commit 142781e108b13b2b0e8f035cfb5bfbbc8f14d887 and fixed in 7.3-rc1 with commit 4a3591287fb7f808e209b4974ed337f609a2006b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89603
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	include/linux/entry-common.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/459f33f82864723a7fa366cf1091d9c6c893b6b2
	https://git.kernel.org/stable/c/ab4647459098a43e9d6fdb860836f08c962f3774
	https://git.kernel.org/stable/c/4a3591287fb7f808e209b4974ed337f609a2006b