ntfs: bound the free-cluster bitmap scan to the volume

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vol->lcn_empty_bits_per_page is sized from vol->nr_clusters at mount, but
ntfs_cluster_alloc() bounds its scan of that array by the size of $Bitmap.
Those are independent on-disk quantities and the mount-time check only
rejects a $Bitmap that is too small, so an image whose $Bitmap covers more
clusters than the volume has lets the scan index past the array.  A run
whose LCN lies in that gap takes the allocator straight there, since the
caller passes the file's own last LCN as its locality hint.  KASAN reports
a slab out-of-bounds read when a file on such a volume is extended.

Clamp the scan to what that array covers, mirroring the max_index
calculation the mount-time scan already uses, and reject a decoded LCN
at or beyond nr_clusters in the mapping pairs decoder.  Conforming
volumes are unaffected.

Fixes: 11ccc9107d ("ntfs: update runlist handling and cluster allocator")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

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Bryam Vargas 2026-07-26 18:29:11 -05:00 • committed by Namjae Jeon

parent 4d730a4dd7

commit 19cac7902a

2 changed files with 13 additions and 1 deletions

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7

fs/ntfs/lcnalloc.c

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7

fs/ntfs/runlist.c

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