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

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().]

Timeline

1. May 27, 2026, 12:18 PM UTCCVE published
2. Oct 16, 2026, 3:18 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 19, 2026, 7:26 PM UTCRecord last updated

Affected versions

• Linux Linux

  From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 1403989d1b502f4a2c0d0b42ccf1c25748442eff; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 1cae1bafdf9caa9b462b19af06b1a06902e4e142; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 764c3c84b5683e608f43735c803a5f415046686c; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in d87268326b277af3665237ac76a73dd9fa8e21b4; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 87d4954b5c59735a99ea98cb208d47130f6dce7d; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 6d76febba07c40bcf358f63216d36ea68cf1c215; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in 815ddd27c0c7171a99fe802fdb19098ddef8b19d; From d0a22a4b03b8475b7aa3fa41243c26c291407844 · fixed in faddeb848305e79db89ee0479bb0e33380656321

• Linux Linux

  5.2

• KernelLinux

  From 5.2.0 · fixed in 5.10.252; From 5.11.0 · fixed in 5.15.202; From 5.16.0 · fixed in 6.1.165; From 6.2.0 · fixed in 6.6.128; From 6.7.0 · fixed in 6.12.75; From 6.13.0 · fixed in 6.18.14; From 6.19.0 · fixed in 6.19.4

References 8