Summary

fuse: fix livelock in synchronous file put from fuseblk workers

Original description

The description as published by the source.

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

fuse: fix livelock in synchronous file put from fuseblk workers

I observed a hang when running generic/323 against a fuseblk server.
This test opens a file, initiates a lot of AIO writes to that file
descriptor, and closes the file descriptor before the writes complete.
Unsurprisingly, the AIO exerciser threads are mostly stuck waiting for
responses from the fuseblk server:

cat /proc/372265/task/372313/stack

[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]
[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]
[<0>] fuse_do_getattr+0xfc/0x1f0 [fuse]
[<0>] fuse_file_read_iter+0xbe/0x1c0 [fuse]
[<0>] aio_read+0x130/0x1e0
[<0>] io_submit_one+0x542/0x860
[<0>] __x64_sys_io_submit+0x98/0x1a0
[<0>] do_syscall_64+0x37/0xf0
[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53

But the /weird/ part is that the fuseblk server threads are waiting for
responses from itself:

cat /proc/372210/task/372232/stack

[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]
[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]
[<0>] fuse_file_put+0x9a/0xd0 [fuse]
[<0>] fuse_release+0x36/0x50 [fuse]
[<0>] __fput+0xec/0x2b0
[<0>] task_work_run+0x55/0x90
[<0>] syscall_exit_to_user_mode+0xe9/0x100
[<0>] do_syscall_64+0x43/0xf0
[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53

The fuseblk server is fuse2fs so there's nothing all that exciting in
the server itself. So why is the fuse server calling fuse_file_put?
The commit message for the fstest sheds some light on t…

Source: OSV.dev (Open Source Vulnerabilities) NVD OSV

Affected packages

Linux Kernel

[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.38"},{"fixed":"5.10.246"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.196"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.158"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.115"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.54"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.17.4"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2025-40220 linux-lts Fixed in: 6.1.158-r0
Debian DEBIAN-CVE-2025-40220 linux Fixed in: 5.10.247-1
Ubuntu UBUNTU-CVE-2025-40220 linux