In the Linux kernel, the following vulnerability has been resolved:
xfs: fix off-by-one in rtrefcount btree root level validation
xfs_rtrefcountbt_compute_maxlevels() sets
mp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1;
where the trailing "+ 1" already accounts for the inode-root level, so the
deepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must
satisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels).
The two on-disk validation paths, xfs_rtrefcountbt_verify() and
xfs_iformat_rtrefcount(), check the root level with ">" instead of ">=", so a
crafted rtreflink (metadir + realtime + reflink) image whose
/rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on
mount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1,
exceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is
sized for exactly bc_maxlevels entries, the first btree op on such a cursor
indexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is
reached by the first rtrefcount cursor built after mount, via log/CoW
recovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an
FS_IOC_GETFSMAP over the realtime device.
Reject a root level equal to m_rtrefc_maxlevels, matching the ">=" form
already used by the sibling data-device refcount/rmap verifiers and the
in-memory rtrmap verifier.
BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)
Write of size 2 at addr ffff888018391658 by task exploit/144
xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)
xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308)
xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113)
xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085)
xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551)
xfs_mountfs (fs/xfs/xfs_mount.c:1158)
xfs_fs_fill_super (fs/xfs/xfs_super.c:1940)
get_tree_bdev_flags (fs/super.c:1634)
vfs_get_tree (fs/super.c:1694)
path_mount (fs/namespace.c:4161)
__x64_sys_mount (fs/namespace.c:4367)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216
The buggy address is located 8 bytes to the right of
allocated 216-byte region [ffff888018391578, ffff888018391650)
Kernel panic - not syncing: Fatal exception
xfs: fix off-by-one in rtrefcount btree root level validation
xfs_rtrefcountbt_compute_maxlevels() sets
mp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1;
where the trailing "+ 1" already accounts for the inode-root level, so the
deepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must
satisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels).
The two on-disk validation paths, xfs_rtrefcountbt_verify() and
xfs_iformat_rtrefcount(), check the root level with ">" instead of ">=", so a
crafted rtreflink (metadir + realtime + reflink) image whose
/rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on
mount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1,
exceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is
sized for exactly bc_maxlevels entries, the first btree op on such a cursor
indexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is
reached by the first rtrefcount cursor built after mount, via log/CoW
recovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an
FS_IOC_GETFSMAP over the realtime device.
Reject a root level equal to m_rtrefc_maxlevels, matching the ">=" form
already used by the sibling data-device refcount/rmap verifiers and the
in-memory rtrmap verifier.
BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)
Write of size 2 at addr ffff888018391658 by task exploit/144
xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)
xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308)
xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113)
xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085)
xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551)
xfs_mountfs (fs/xfs/xfs_mount.c:1158)
xfs_fs_fill_super (fs/xfs/xfs_super.c:1940)
get_tree_bdev_flags (fs/super.c:1634)
vfs_get_tree (fs/super.c:1694)
path_mount (fs/namespace.c:4161)
__x64_sys_mount (fs/namespace.c:4367)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216
The buggy address is located 8 bytes to the right of
allocated 216-byte region [ffff888018391578, ffff888018391650)
Kernel panic - not syncing: Fatal exception
Metrics
Affected Vendors & Products
Advisories
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Wed, 26 Aug 2026 14:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: xfs: fix off-by-one in rtrefcount btree root level validation xfs_rtrefcountbt_compute_maxlevels() sets mp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1; where the trailing "+ 1" already accounts for the inode-root level, so the deepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must satisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels). The two on-disk validation paths, xfs_rtrefcountbt_verify() and xfs_iformat_rtrefcount(), check the root level with ">" instead of ">=", so a crafted rtreflink (metadir + realtime + reflink) image whose /rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on mount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1, exceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is sized for exactly bc_maxlevels entries, the first btree op on such a cursor indexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is reached by the first rtrefcount cursor built after mount, via log/CoW recovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an FS_IOC_GETFSMAP over the realtime device. Reject a root level equal to m_rtrefc_maxlevels, matching the ">=" form already used by the sibling data-device refcount/rmap verifiers and the in-memory rtrmap verifier. BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) Write of size 2 at addr ffff888018391658 by task exploit/144 xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308) xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113) xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085) xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551) xfs_mountfs (fs/xfs/xfs_mount.c:1158) xfs_fs_fill_super (fs/xfs/xfs_super.c:1940) get_tree_bdev_flags (fs/super.c:1634) vfs_get_tree (fs/super.c:1694) path_mount (fs/namespace.c:4161) __x64_sys_mount (fs/namespace.c:4367) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216 The buggy address is located 8 bytes to the right of allocated 216-byte region [ffff888018391578, ffff888018391650) Kernel panic - not syncing: Fatal exception | |
| Title | xfs: fix off-by-one in rtrefcount btree root level validation | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-08-26T14:37:12.180Z
Reserved: 2026-08-26T14:34:25.765Z
Link: CVE-2026-80537
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-26T15:17:07.890
Modified: 2026-08-26T15:17:07.890
Link: CVE-2026-80537
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.