HIGH
f2fs NodeInode Race
CVE-2026-31715
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI4.6MEDIUM
01Description
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.
02KernelScan AI Analysis
Risk summary
A race condition in F2FS filesystem between write I/O completion and unmount operations can cause a kernel panic. Systems using F2FS filesystems with concurrent I/O and mount/unmount operations are at risk of denial of service through system crashes.
Vulnerability analysis
The vulnerability occurs when f2fs_write_end_io() accesses sbi->node_inode after f2fs_put_super() has freed it during unmount. The race happens because the write callback decrements the page count first, allowing the unmount to proceed and NULL the node_inode pointer before f2fs_in_warm_node_list() tries to access it. The fix reorders operations to check the warm node list before decrementing the page count, preventing the unmount from proceeding until after the node_inode access is complete.
03Fix Versions
| Branch | Fixed in | Patch commit |
|---|---|---|
| 6.12 | 6.12.86 | 7be222de96c0 |
| 6.18 | 6.18.25 | 963d2e24d9d9 |
| 6.6 | 6.6.140 | 1171f329cf1c |
| 7.0 | 7.0.2 | 188bb65f247a |
| mainline | 7.1-rc1 | 2d9c4a4ed4ee |