linux-cve-announce - CVE-2026-23199: procfs: avoid fetching build ID while holding VMA lock

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Message-ID: <2026021436-CVE-2026-23199-0dc0@gregkh>
Date: Sat, 14 Feb 2026 17:28:56 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2026-23199: procfs: avoid fetching build ID while holding VMA lock

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

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

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

procfs: avoid fetching build ID while holding VMA lock

Fix PROCMAP_QUERY to fetch optional build ID only after dropping mmap_lock
or per-VMA lock, whichever was used to lock VMA under question, to avoid
deadlock reported by syzbot:

 -> #1 (&mm->mmap_lock){++++}-{4:4}:
        __might_fault+0xed/0x170
        _copy_to_iter+0x118/0x1720
        copy_page_to_iter+0x12d/0x1e0
        filemap_read+0x720/0x10a0
        blkdev_read_iter+0x2b5/0x4e0
        vfs_read+0x7f4/0xae0
        ksys_read+0x12a/0x250
        do_syscall_64+0xcb/0xf80
        entry_SYSCALL_64_after_hwframe+0x77/0x7f

 -> #0 (&sb->s_type->i_mutex_key#8){++++}-{4:4}:
        __lock_acquire+0x1509/0x26d0
        lock_acquire+0x185/0x340
        down_read+0x98/0x490
        blkdev_read_iter+0x2a7/0x4e0
        __kernel_read+0x39a/0xa90
        freader_fetch+0x1d5/0xa80
        __build_id_parse.isra.0+0xea/0x6a0
        do_procmap_query+0xd75/0x1050
        procfs_procmap_ioctl+0x7a/0xb0
        __x64_sys_ioctl+0x18e/0x210
        do_syscall_64+0xcb/0xf80
        entry_SYSCALL_64_after_hwframe+0x77/0x7f

 other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   rlock(&mm->mmap_lock);
                                lock(&sb->s_type->i_mutex_key#8);
                                lock(&mm->mmap_lock);
   rlock(&sb->s_type->i_mutex_key#8);

  *** DEADLOCK ***

This seems to be exacerbated (as we haven't seen these syzbot reports
before that) by the recent:

	777a8560fd29 ("lib/buildid: use __kernel_read() for sleepable context")

To make this safe, we need to grab file refcount while VMA is still locked, but
other than that everything is pretty straightforward. Internal build_id_parse()
API assumes VMA is passed, but it only needs the underlying file reference, so
just add another variant build_id_parse_file() that expects file passed
directly.

[akpm@...ux-foundation.org: fix up kerneldoc]

The Linux kernel CVE team has assigned CVE-2026-23199 to this issue.


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

	Issue introduced in 6.11 with commit ed5d583a88a9207b866c14ba834984c6f3c51d23 and fixed in 6.12.70 with commit b9b97e6aeb534315f9646b2090d1a5024c6a4e82
	Issue introduced in 6.11 with commit ed5d583a88a9207b866c14ba834984c6f3c51d23 and fixed in 6.18.10 with commit cbc03ce3e6ce7e21214c3f02218213574c1a2d08
	Issue introduced in 6.11 with commit ed5d583a88a9207b866c14ba834984c6f3c51d23 and fixed in 6.19 with commit b5cbacd7f86f4f62b8813688c8e73be94e8e1951

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-2026-23199
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:
	fs/proc/task_mmu.c
	include/linux/buildid.h
	lib/buildid.c


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/b9b97e6aeb534315f9646b2090d1a5024c6a4e82
	https://git.kernel.org/stable/c/cbc03ce3e6ce7e21214c3f02218213574c1a2d08
	https://git.kernel.org/stable/c/b5cbacd7f86f4f62b8813688c8e73be94e8e1951