CVE-2026-45984

Summary

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

gfs2: Fix use-after-free in iomap inline data write path

The inline data buffer head (dibh) is being released prematurely in gfs2_iomap_begin() via release_metapath() while iomap->inline_data still points to dibh->b_data. This causes a use-after-free when iomap_write_end_inline() later attempts to write to the inline data area.

The bug sequence:

1. gfs2_iomap_begin() calls gfs2_meta_inode_buffer() to read inode metadata into dibh
2. Sets iomap->inline_data = dibh->b_data + sizeof(struct gfs2_dinode)
3. Calls release_metapath() which calls brelse(dibh), dropping refcount to 0
4. kswapd reclaims the page (~39ms later in the syzbot report)
5. iomap_write_end_inline() tries to memcpy() to iomap->inline_data
6. KASAN detects use-after-free write to freed memory

Fix by storing dibh in iomap->private and incrementing its refcount with get_bh() in gfs2_iomap_begin(). The buffer is then properly released in gfs2_iomap_end() after the inline write completes, ensuring the page stays alive for the entire iomap operation.

Note: A C reproducer is not available for this issue. The fix is based on analysis of the KASAN report and code review showing the buffer head is freed before use.

[agruenba: Take buffer head reference in gfs2_iomap_begin() to avoid leaks in gfs2_iomap_get() and gfs2_iomap_alloc().]

Affected Software

Weaknesses

ADP Enrichment

kernel: gfs2: Fix use-after-free in iomap inline data write path

Additional References

• https://access.redhat.com/security/cve/CVE-2026-45984
• https://bugzilla.redhat.com/show_bug.cgi?id=2481922
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-45984.json
• https://access.redhat.com/errata/RHSA-2026:27789
• https://access.redhat.com/errata/RHSA-2026:33743

References

• https://git.kernel.org/stable/c/1403989d1b502f4a2c0d0b42ccf1c25748442eff
• https://git.kernel.org/stable/c/1cae1bafdf9caa9b462b19af06b1a06902e4e142
• https://git.kernel.org/stable/c/764c3c84b5683e608f43735c803a5f415046686c
• https://git.kernel.org/stable/c/d87268326b277af3665237ac76a73dd9fa8e21b4
• https://git.kernel.org/stable/c/87d4954b5c59735a99ea98cb208d47130f6dce7d
• https://git.kernel.org/stable/c/6d76febba07c40bcf358f63216d36ea68cf1c215
• https://git.kernel.org/stable/c/815ddd27c0c7171a99fe802fdb19098ddef8b19d
• https://git.kernel.org/stable/c/faddeb848305e79db89ee0479bb0e33380656321

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