CVE-2026-31715
Received Received - Intake
Use-After-Free in F2FS Linux Kernel

Publication date: 2026-05-01

Last updated on: 2026-05-01

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: f2fs: fix UAF caused by decrementing sbi->nr_pages[] in f2fs_write_end_io() The xfstests case "generic/107" and syzbot have both reported a NULL pointer dereference. The concurrent scenario that triggers the panic is as follows: F2FS_WB_CP_DATA write callback umount - f2fs_write_checkpoint - f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA) - blk_mq_end_request - bio_endio - f2fs_write_end_io : dec_page_count(sbi, F2FS_WB_CP_DATA) : wake_up(&sbi->cp_wait) - kill_f2fs_super - kill_block_super - f2fs_put_super : iput(sbi->node_inode) : sbi->node_inode = NULL : f2fs_in_warm_node_list - is_node_folio // sbi->node_inode is NULL and panic The root cause is that f2fs_put_super() calls iput(sbi->node_inode) and sets sbi->node_inode to NULL after sbi->nr_pages[F2FS_WB_CP_DATA] is decremented to zero. As a result, f2fs_in_warm_node_list() may dereference a NULL node_inode when checking whether a folio belongs to the node inode, leading to a panic. This patch fixes the issue by calling f2fs_in_warm_node_list() before decrementing sbi->nr_pages[F2FS_WB_CP_DATA], thus preventing the use-after-free condition.
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Meta Information
Published
2026-05-01
Last Modified
2026-05-01
Generated
2026-05-07
AI Q&A
2026-05-01
EPSS Evaluated
2026-05-05
NVD
CVE-2026-31715
EUVD
EUVD-2026-26524
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is a use-after-free (UAF) issue in the Linux kernel's f2fs filesystem. It occurs because the function f2fs_put_super() calls iput() on sbi->node_inode and then sets sbi->node_inode to NULL after decrementing sbi->nr_pages[F2FS_WB_CP_DATA] to zero. Subsequently, the function f2fs_in_warm_node_list() may attempt to dereference this now NULL node_inode pointer, leading to a kernel panic.

The problem arises in a concurrent scenario involving write callbacks and unmount operations, where the order of operations causes the use-after-free condition. The fix involves changing the order of operations by calling f2fs_in_warm_node_list() before decrementing sbi->nr_pages[F2FS_WB_CP_DATA], preventing the NULL pointer dereference.


How can this vulnerability impact me? :

This vulnerability can cause the Linux kernel to panic due to a NULL pointer dereference, leading to a system crash. Such a crash can result in denial of service, data loss, or system instability, especially on systems using the f2fs filesystem.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability is fixed by a patch that changes the order of operations in the f2fs filesystem code to prevent a use-after-free condition. Immediate mitigation involves updating the Linux kernel to a version that includes this fix.

  • Apply the patch or upgrade to a Linux kernel version released after 2026-05-01 that contains the fix for the f2fs use-after-free issue.
  • Avoid unmounting f2fs filesystems during heavy write operations until the fix is applied, as the panic occurs during concurrent write and unmount operations.

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