CVE-2025-38139 netfs: Fix oops in write-retry from mis-resetting the subreq iterator
A memory corruption flaw in the Linux kernel netfs subsystem allows local attackers to cause a system crash via a slab-out-of-bounds read during write retries.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38139?
CVE-2025-38139 is a critical memory corruption vulnerability in Linux kernel, published on 3 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix oops in write-retry from mis-resetting the subreq iterator
Fix the resetting of the subrequest iterator in netfs_retry_write_stream() to use the iterator-reset function as the iterator may have been shortened by a previous retry. In such a case, the amount of data to be written by the subrequest is not "subreq->len" but "subreq->len - subreq->transferred".
Without this, KASAN may see an error in iov_iter_revert():
BUG: KASAN: slab-out-of-bounds in iov_iter_revert lib/iov_iter.c:633 [inline] BUG: KASAN: slab-out-of-bounds in iov_iter_revert+0x443/0x5a0 lib/iov_iter.c:611 Read of size 4 at addr ffff88802912a0b8 by task kworker/u32:7/1147
CPU: 1 UID: 0 PID: 1147 Comm: kworker/u32:7 Not tainted 6.15.0-rc6-syzkaller-00052-g9f35e33144ae #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: events_unbound netfs_write_collection_worker Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xc3/0x670 mm/kasan/report.c:521 kasan_report+0xe0/0x110 mm/kasan/report.c:634 iov_iter_revert lib/iov_iter.c:633 [inline] iov_iter_revert+0x443/0x5a0 lib/iov_iter.c:611 netfs_retry_write_stream fs/netfs/write_retry.c:44 [inline] netfs_retry_writes+0x166d/0x1a50 fs/netfs/write_retry.c:231 netfs_collect_write_results fs/netfs/write_collect.c:352 [inline] netfs_write_collection_worker+0x23fd/0x3830 fs/netfs/write_collect.c:374 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400 kthread+0x3c2/0x780 kernel/kthread.c:464 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK>
Weakness: CWE-125
Which versions are affected by CVE-2025-38139?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-38139?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-38139 being exploited?
There is no known exploitation of CVE-2025-38139 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-38139, DEBIAN-CVE-2025-38139, GHSA-fm2c-q6px-5rp9, UBUNTU-CVE-2025-38139.