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CVE-2025-40220— fuse: fix livelock in synchronous file put from fuseblk workers

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于fuse同步文件放置中的活锁问题，可能导致服务不可用。

AI Predicted 5.9 Difficulty: Easy EPSS 0.19% · P8

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 26

VendorProduct Version RangeStatus
Linux Linux 5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< 548e1f2bac1d4df91a6138f26bb4ab00323fd948 affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< cfd1aa3e2b71f3327cb373c45a897c9028c62b35 affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< 83b375c6efef69b1066ad2d79601221e7892745a affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< bfd17b6138df0122a95989457d8e18ce0b86165e affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< b26923512dbe57ae4917bafd31396d22a9d1691a affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< f19a1390af448d9e193c08e28ea5f727bf3c3049 affected
5a18ec176c934ca1bc9dc61580a5e0e90a9b5733< 26e5c67deb2e1f42a951f022fdf5b9f7eb747b01 affected
9efe56738fecd591b5bf366a325440f9b457ebd6 affected
… +18 more rows
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I. Basic Information for CVE-2025-40220

Vulnerability Information
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Vulnerability Title
fuse: fix livelock in synchronous file put from fuseblk workers
Source: CVE Program / CVE List V5
Vulnerability Description
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 that: "By closing the file descriptor before calling io_destroy, you pretty much guarantee that the last put on the ioctx will be done in interrupt context (during I/O completion). Aha. AIO fgets a new struct file from the fd when it queues the ioctx. The completion of the FUSE_WRITE command from userspace causes the fuse server to call the AIO completion function. The completion puts the struct file, queuing a delayed fput to the fuse server task. When the fuse server task returns to userspace, it has to run the delayed fput, which in the case of a fuseblk server, it does synchronously. Sending the FUSE_RELEASE command sychronously from fuse server threads is a bad idea because a client program can initiate enough simultaneous AIOs such that all the fuse server threads end up in delayed_fput, and now there aren't any threads left to handle the queued fuse commands. Fix this by only using asynchronous fputs when closing files, and leave a comment explaining why.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于fuse同步文件放置中的活锁问题，可能导致服务不可用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 5a18ec176c934ca1bc9dc61580a5e0e90a9b5733 ~ 548e1f2bac1d4df91a6138f26bb4ab00323fd948 -
Linux Linux 2.6.38 -

II. Public POCs for CVE-2025-40220

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III. Intelligence Information for CVE-2025-40220

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Same Patch Batch · Linux · 2025-12-04 · 53 CVEs total

CVE-2025-40261 9.8 CRITICAL nvme: nvme-fc: Ensure ->ioerr_work is cancelled in nvme_fc_delete_ctrl()
CVE-2025-40252 9.8 CRITICAL net: qlogic/qede: fix potential out-of-bounds read in qede_tpa_cont() and qede_tpa_end()
CVE-2025-40258 9.8 CRITICAL mptcp: fix race condition in mptcp_schedule_work()
CVE-2025-40257 9.8 CRITICAL mptcp: fix a race in mptcp_pm_del_add_timer()
CVE-2025-40253 8.8 HIGH s390/ctcm: Fix double-kfree
CVE-2025-40266 8.2 HIGH KVM: arm64: Check the untrusted offset in FF-A memory share
CVE-2025-40244 7.8 HIGH hfsplus: fix KMSAN uninit-value issue in __hfsplus_ext_cache_extent()
CVE-2025-40251 7.8 HIGH devlink: rate: Unset parent pointer in devl_rate_nodes_destroy
CVE-2025-40262 7.8 HIGH Input: imx_sc_key - fix memory corruption on unload
CVE-2025-40250 7.8 HIGH net/mlx5: Clean up only new IRQ glue on request_irq() failure
CVE-2025-40248 7.8 HIGH vsock: Ignore signal/timeout on connect() if already established
CVE-2025-40249 7.8 HIGH gpio: cdev: make sure the cdev fd is still active before emitting events
CVE-2025-40245 7.8 HIGH nios2: ensure that memblock.current_limit is set when setting pfn limits
CVE-2025-40214 7.8 HIGH af_unix: Initialise scc_index in unix_add_edge().
CVE-2025-40243 7.8 HIGH hfs: fix KMSAN uninit-value issue in hfs_find_set_zero_bits()
CVE-2025-40241 7.8 HIGH erofs: fix crafted invalid cases for encoded extents
CVE-2025-40233 7.8 HIGH ocfs2: clear extent cache after moving/defragmenting extents
CVE-2025-40216 7.8 HIGH io_uring/rsrc: don't rely on user vaddr alignment
CVE-2025-40215 7.8 HIGH xfrm: delete x->tunnel as we delete x
CVE-2025-40240 7.5 HIGH sctp: avoid NULL dereference when chunk data buffer is missing

Showing top 20 of 53 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2025-40220

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