ext4: use fsdata to track inline data write state and fix race

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Summary

CVECVE-2026-92500
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:17:52 UTC
Updated2026-09-17 17:17:52 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ext4: use fsdata to track inline data write state and fix race Instead of checking the live inode state (ext4_has_inline_data(inode) and ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)) in the write_end handlers, use the fsdata parameter of the address space operations to explicitly pass down the state in which write_begin prepared the write. A concurrent thread (such as ext4_page_mkwrite()) can convert the inline data to an extent between write_begin and write_end. If this happens, the write_end handlers would previously miss the inline write_end path and fall through to extent-based write_end logic. However, since block buffers were never allocated in write_begin, this resulted in NULL pointer dereferences or data loss because folio_buffers(folio) was NULL. Define EXT4_WRITE_DATA_INLINE (4) as a bit flag (Bit 2), treating fsdata as bitwise flags rather than mutually exclusive enums to keep states of the write path independent. Communicate this state via fsdata: 1) ext4_write_begin() and ext4_da_write_begin() set the EXT4_WRITE_DATA_INLINE bit in *fsdata via bitwise OR when an inline write is successfully prepared. 2) On entry, ext4_write_begin() clears the EXT4_WRITE_DATA_INLINE bit to safely handle VFS retries (where generic_perform_write() bypasses the fsdata initialization on its retry jump). 3) The write_end handlers perform a bitwise AND to check if the EXT4_WRITE_DATA_INLINE bit is set and invoke the inline write_end helper accordingly. Furthermore, during a buffered write, ext4_write_inline_data_end() acquires the xattr lock after preparing the write. If a concurrent page fault (ext4_page_mkwrite()) converts the inline data to an extent after the write_end handlers check the state but before ext4_write_inline_data_end() acquires the xattr write lock, the subsequent check will trigger a kernel panic via BUG_ON(!ext4_has_inline_data(inode)). To keep git history working and bisectability clean, replace the BUG_ON check in ext4_write_inline_data_end() with a graceful error- handling retry path in this same commit. If the inline data is cleared after locking the xattr, we safely release all resources (releasing iloc.bh, unlocking/putting the folio, stopping the active journal transaction handle) and return 0 (VFS retry) to let the generic write path retry the operation safely.

Risk And Classification

EPSS: 0.001760000 probability, percentile 0.074060000 (date 2026-09-18)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3fdcfb668fd78ec92d9bc2daddf1d41e2a8a30bb bd8d74bd46d09905164255b8635fa58b45f41068 git Not specified
CNA Linux Linux affected 3fdcfb668fd78ec92d9bc2daddf1d41e2a8a30bb 439aedfd7ae868d1d7b4930afe66091cb979cd5c git Not specified
CNA Linux Linux affected 3fdcfb668fd78ec92d9bc2daddf1d41e2a8a30bb 7edbb323bab2b2a609016014caafdb651c898249 git Not specified
CNA Linux Linux affected 3.8 Not specified
CNA Linux Linux unaffected 3.8 semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/439aedfd7ae868d1d7b4930afe66091cb979cd5c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7edbb323bab2b2a609016014caafdb651c898249 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bd8d74bd46d09905164255b8635fa58b45f41068 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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