md/md-llbitmap: prevent create failure bitmap UAF

Summary

In the Linux kernel, the following vulnerability has been resolved: md/md-llbitmap: prevent create failure bitmap UAF llbitmap_create() publishes mddev->bitmap before reading the bitmap superblock. This is needed because llbitmap_read_sb() can initialize a new bitmap and flush it through helpers that use mddev->bitmap. If llbitmap_read_sb() fails, the old cleanup dropped bitmap_info.mutex and freed llbitmap before clearing mddev->bitmap. Readers such as /proc/mdstat rely on bitmap_info.mutex to keep the bitmap pointer stable while collecting bitmap stats, so they could observe the stale pointer after the failed create path released the mutex. Clear mddev->bitmap while still holding bitmap_info.mutex, then free the failed llbitmap after dropping the mutex. This makes mutex-protected readers see either a live bitmap or no bitmap.

Timeline

1. Sep 17, 2026, 4:08 PM UTCCVE published
2. Oct 19, 2026, 9:00 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 5ab829f1971dc99f2aac10846c378e67fc875abc · fixed in 930cc4f1af5a1afcd545a6ba00e38921ff8401e0; From 5ab829f1971dc99f2aac10846c378e67fc875abc · fixed in 2f0722435ce3a844dbb66b9bb0a18229dcc8739c; From 5ab829f1971dc99f2aac10846c378e67fc875abc · fixed in 2116c2f0a0e547615886900e2ed8c529c016499b

• Linux Linux

  6.18

• KernelLinux

  From 6.18.0 · fixed in 6.18.52; From 6.19.0 · fixed in 7.2.6

References 3