CVE-2026-93235

Summary

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to zero post-EOF data when extending file size

generic/794 4s … - output mismatch (see /share/git/fstests/results//generic/794.out.bad) — tests/generic/794.out 2026-06-12 08:46:32.766426241 +0800 +++ /share/git/fstests/results//generic/794.out.bad 2026-07-05 18:32:55.000000000 +0800 @@ -1,4 +1,16 @@ QA output created by 794 append_write +FAIL: non-zero data in gap [4080,4096) after shutdown+remount +000000 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >ZZZZZZZZZZZZZZZZ< +* +001000 truncate_up … (Run 'diff -u /share/git/fstests/tests/generic/794.out /share/git/fstests/results//generic/794.out.bad' to see the entire diff) Ran: generic/794 Failures: generic/794 Failed 1 of 1 tests

Steps of generic/794:

1. write 4096 bytes to file w/ 0x5a
2. use fiemap to get PBA of first block in file
3. truncate file to 4080
4. umount; write 4096 bytes to file w/ 0x5a directly via PBA; mount
5. extend filesize via a) append 4096 from offset 4096, or b) truncate 8192, or c) fallocate 4096 from offset 4096
6. verify the gap is zeroed in memory [4080,4096)
7. sync range 4096 from offset 4096; shutdown -f (flush meta before shutdown)
8. umount; mount; verify [4080,4096) is zeroed or not.

When extending file size (e.g. via truncate, fallocate, or write) across an unaligned EOF boundary, we need to ensure that post-EOF data in the partial page is zeroed out in pagecache and marked dirty, then writeback the cache to persist zeroed data before committing inode w/ updated i_size.

This help to prevent stale disk data beyond the previous EOF from being exposed after remounting or crash recovery.

Since f2fs is a LFS filesystem, we only support direct write via PBA in pinfile, and pinfile has section-aligned filesize, so in Android, there should no problem, but for other usage in different environment, let's fix this w/ fsync_mode=strict mount option.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/6882d458d2e403f6ba7b45542dd31a6b7531eb2e
• https://git.kernel.org/stable/c/32c7f11a24268ba8d3bb50ea7f54d33f698cd253
• https://git.kernel.org/stable/c/91ec55ddc097ccddd25ffb95a3d079b2ef362372
• https://git.kernel.org/stable/c/c42608c09b6b5d5967bf211c255914c068c2cde1
• https://git.kernel.org/stable/c/5eced87b7d19dbc76ebdddaf322046f9ac582fcb

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