GHSA-P99W-MP33-JG8X
Vulnerability from github – Published: 2026-03-04 15:30 – Updated: 2026-03-04 15:30In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to avoid mapping wrong physical block for swapfile
Xiaolong Guo reported a f2fs bug in bugzilla [1]
[1] https://bugzilla.kernel.org/show_bug.cgi?id=220951
Quoted:
"When using stress-ng's swap stress test on F2FS filesystem with kernel 6.6+, the system experiences data corruption leading to either: 1 dm-verity corruption errors and device reboot 2 F2FS node corruption errors and boot hangs
The issue occurs specifically when: 1 Using F2FS filesystem (ext4 is unaffected) 2 Swapfile size is less than F2FS section size (2MB) 3 Swapfile has fragmented physical layout (multiple non-contiguous extents) 4 Kernel version is 6.6+ (6.1 is unaffected)
The root cause is in check_swap_activate() function in fs/f2fs/data.c. When the first extent of a small swapfile (< 2MB) is not aligned to section boundaries, the function incorrectly treats it as the last extent, failing to map subsequent extents. This results in incorrect swap_extent creation where only the first extent is mapped, causing subsequent swap writes to overwrite wrong physical locations (other files' data).
Steps to Reproduce 1 Setup a device with F2FS-formatted userdata partition 2 Compile stress-ng from https://github.com/ColinIanKing/stress-ng 3 Run swap stress test: (Android devices) adb shell "cd /data/stressng; ./stress-ng-64 --metrics-brief --timeout 60 --swap 0"
Log: 1 Ftrace shows in kernel 6.6, only first extent is mapped during second f2fs_map_blocks call in check_swap_activate(): stress-ng-swap-8990: f2fs_map_blocks: ino=11002, file offset=0, start blkaddr=0x43143, len=0x1 (Only 4KB mapped, not the full swapfile) 2 in kernel 6.1, both extents are correctly mapped: stress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=0, start blkaddr=0x13cd4, len=0x1 stress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=1, start blkaddr=0x60c84b, len=0xff
The problematic code is in check_swap_activate(): if ((pblock - SM_I(sbi)->main_blkaddr) % blks_per_sec || nr_pblocks % blks_per_sec || !f2fs_valid_pinned_area(sbi, pblock)) { bool last_extent = false;
not_aligned++;
nr_pblocks = roundup(nr_pblocks, blks_per_sec);
if (cur_lblock + nr_pblocks > sis->max)
nr_pblocks -= blks_per_sec;
/* this extent is last one */
if (!nr_pblocks) {
nr_pblocks = last_lblock - cur_lblock;
last_extent = true;
}
ret = f2fs_migrate_blocks(inode, cur_lblock, nr_pblocks);
if (ret) {
if (ret == -ENOENT)
ret = -EINVAL;
goto out;
}
if (!last_extent)
goto retry;
}
When the first extent is unaligned and roundup(nr_pblocks, blks_per_sec) exceeds sis->max, we subtract blks_per_sec resulting in nr_pblocks = 0. The code then incorrectly assumes this is the last extent, sets nr_pblocks = last_lblock - cur_lblock (entire swapfile), and performs migration. After migration, it doesn't retry mapping, so subsequent extents are never processed. "
In order to fix this issue, we need to lookup block mapping info after we migrate all blocks in the tail of swapfile.
{
"affected": [],
"aliases": [
"CVE-2026-23233"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-03-04T15:16:13Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nf2fs: fix to avoid mapping wrong physical block for swapfile\n\nXiaolong Guo reported a f2fs bug in bugzilla [1]\n\n[1] https://bugzilla.kernel.org/show_bug.cgi?id=220951\n\nQuoted:\n\n\"When using stress-ng\u0027s swap stress test on F2FS filesystem with kernel 6.6+,\nthe system experiences data corruption leading to either:\n1 dm-verity corruption errors and device reboot\n2 F2FS node corruption errors and boot hangs\n\nThe issue occurs specifically when:\n1 Using F2FS filesystem (ext4 is unaffected)\n2 Swapfile size is less than F2FS section size (2MB)\n3 Swapfile has fragmented physical layout (multiple non-contiguous extents)\n4 Kernel version is 6.6+ (6.1 is unaffected)\n\nThe root cause is in check_swap_activate() function in fs/f2fs/data.c. When the\nfirst extent of a small swapfile (\u003c 2MB) is not aligned to section boundaries,\nthe function incorrectly treats it as the last extent, failing to map\nsubsequent extents. This results in incorrect swap_extent creation where only\nthe first extent is mapped, causing subsequent swap writes to overwrite wrong\nphysical locations (other files\u0027 data).\n\nSteps to Reproduce\n1 Setup a device with F2FS-formatted userdata partition\n2 Compile stress-ng from https://github.com/ColinIanKing/stress-ng\n3 Run swap stress test: (Android devices)\nadb shell \"cd /data/stressng; ./stress-ng-64 --metrics-brief --timeout 60\n--swap 0\"\n\nLog:\n1 Ftrace shows in kernel 6.6, only first extent is mapped during second\nf2fs_map_blocks call in check_swap_activate():\nstress-ng-swap-8990: f2fs_map_blocks: ino=11002, file offset=0, start\nblkaddr=0x43143, len=0x1\n(Only 4KB mapped, not the full swapfile)\n2 in kernel 6.1, both extents are correctly mapped:\nstress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=0, start\nblkaddr=0x13cd4, len=0x1\nstress-ng-swap-5966: f2fs_map_blocks: ino=28011, file offset=1, start\nblkaddr=0x60c84b, len=0xff\n\nThe problematic code is in check_swap_activate():\nif ((pblock - SM_I(sbi)-\u003emain_blkaddr) % blks_per_sec ||\n nr_pblocks % blks_per_sec ||\n !f2fs_valid_pinned_area(sbi, pblock)) {\n bool last_extent = false;\n\n not_aligned++;\n\n nr_pblocks = roundup(nr_pblocks, blks_per_sec);\n if (cur_lblock + nr_pblocks \u003e sis-\u003emax)\n nr_pblocks -= blks_per_sec;\n\n /* this extent is last one */\n if (!nr_pblocks) {\n nr_pblocks = last_lblock - cur_lblock;\n last_extent = true;\n }\n\n ret = f2fs_migrate_blocks(inode, cur_lblock, nr_pblocks);\n if (ret) {\n if (ret == -ENOENT)\n ret = -EINVAL;\n goto out;\n }\n\n if (!last_extent)\n goto retry;\n}\n\nWhen the first extent is unaligned and roundup(nr_pblocks, blks_per_sec)\nexceeds sis-\u003emax, we subtract blks_per_sec resulting in nr_pblocks = 0. The\ncode then incorrectly assumes this is the last extent, sets nr_pblocks =\nlast_lblock - cur_lblock (entire swapfile), and performs migration. After\nmigration, it doesn\u0027t retry mapping, so subsequent extents are never processed.\n\"\n\nIn order to fix this issue, we need to lookup block mapping info after\nwe migrate all blocks in the tail of swapfile.",
"id": "GHSA-p99w-mp33-jg8x",
"modified": "2026-03-04T15:30:36Z",
"published": "2026-03-04T15:30:36Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23233"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1ff415eef513bf12deb058fc50d57788c46c48e6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5c145c03188bc9ba1c29e0bc4d527a5978fc47f9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/607cb9d83838d2cd9f0406c2403ed61aadf0edff"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d4534a7f6c92baaf7e12a45fc6e37332cafafc33"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fee27b69dde1a05908b350eea42937af2387c4fe"
}
],
"schema_version": "1.4.0",
"severity": []
}
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