linux-cve-announce - CVE-2025-68821: fuse: fix readahead reclaim deadlock

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Message-ID: <2026011315-CVE-2025-68821-b515@gregkh>
Date: Tue, 13 Jan 2026 16:29:47 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68821: fuse: fix readahead reclaim deadlock

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

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

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

fuse: fix readahead reclaim deadlock

Commit e26ee4efbc79 ("fuse: allocate ff->release_args only if release is
needed") skips allocating ff->release_args if the server does not
implement open. However in doing so, fuse_prepare_release() now skips
grabbing the reference on the inode, which makes it possible for an
inode to be evicted from the dcache while there are inflight readahead
requests. This causes a deadlock if the server triggers reclaim while
servicing the readahead request and reclaim attempts to evict the inode
of the file being read ahead. Since the folio is locked during
readahead, when reclaim evicts the fuse inode and fuse_evict_inode()
attempts to remove all folios associated with the inode from the page
cache (truncate_inode_pages_range()), reclaim will block forever waiting
for the lock since readahead cannot relinquish the lock because it is
itself blocked in reclaim:

>>> stack_trace(1504735)
 folio_wait_bit_common (mm/filemap.c:1308:4)
 folio_lock (./include/linux/pagemap.h:1052:3)
 truncate_inode_pages_range (mm/truncate.c:336:10)
 fuse_evict_inode (fs/fuse/inode.c:161:2)
 evict (fs/inode.c:704:3)
 dentry_unlink_inode (fs/dcache.c:412:3)
 __dentry_kill (fs/dcache.c:615:3)
 shrink_kill (fs/dcache.c:1060:12)
 shrink_dentry_list (fs/dcache.c:1087:3)
 prune_dcache_sb (fs/dcache.c:1168:2)
 super_cache_scan (fs/super.c:221:10)
 do_shrink_slab (mm/shrinker.c:435:9)
 shrink_slab (mm/shrinker.c:626:10)
 shrink_node (mm/vmscan.c:5951:2)
 shrink_zones (mm/vmscan.c:6195:3)
 do_try_to_free_pages (mm/vmscan.c:6257:3)
 do_swap_page (mm/memory.c:4136:11)
 handle_pte_fault (mm/memory.c:5562:10)
 handle_mm_fault (mm/memory.c:5870:9)
 do_user_addr_fault (arch/x86/mm/fault.c:1338:10)
 handle_page_fault (arch/x86/mm/fault.c:1481:3)
 exc_page_fault (arch/x86/mm/fault.c:1539:2)
 asm_exc_page_fault+0x22/0x27

Fix this deadlock by allocating ff->release_args and grabbing the
reference on the inode when preparing the file for release even if the
server does not implement open. The inode reference will be dropped when
the last reference on the fuse file is dropped (see fuse_file_put() ->
fuse_release_end()).

The Linux kernel CVE team has assigned CVE-2025-68821 to this issue.


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

	Issue introduced in 6.1.158 with commit 7d38aa079ed859b73f4460aab89c7619b04963b8 and fixed in 6.1.160 with commit 4703bc0e8cd3409acb1476a70cb5b7ff943cf39a
	Issue introduced in 6.6.115 with commit c7ec75f3cbf73bd46f479f7d6942585f765715da and fixed in 6.6.120 with commit cf74785c00b8b1c0c4a9dd74bfa9c22d62e2d99f
	Issue introduced in 6.9 with commit e26ee4efbc79610b20e7abe9d96c87f33dacc1ff and fixed in 6.12.64 with commit fbba8b00bbe4e4f958a2b0654cc1219a7e6597f6
	Issue introduced in 6.9 with commit e26ee4efbc79610b20e7abe9d96c87f33dacc1ff and fixed in 6.18.3 with commit e0d6de83a4cc22bbac72713f3a58121af36cc411
	Issue introduced in 6.9 with commit e26ee4efbc79610b20e7abe9d96c87f33dacc1ff and fixed in 6.19-rc1 with commit bd5603eaae0aabf527bfb3ce1bb07e979ce5bd50
	Issue introduced in 5.15.196 with commit a39f70d63f4373a598820d9491719e44cd60afe9

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-2025-68821
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/fuse/file.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/4703bc0e8cd3409acb1476a70cb5b7ff943cf39a
	https://git.kernel.org/stable/c/cf74785c00b8b1c0c4a9dd74bfa9c22d62e2d99f
	https://git.kernel.org/stable/c/fbba8b00bbe4e4f958a2b0654cc1219a7e6597f6
	https://git.kernel.org/stable/c/e0d6de83a4cc22bbac72713f3a58121af36cc411
	https://git.kernel.org/stable/c/bd5603eaae0aabf527bfb3ce1bb07e979ce5bd50