CVE-2026-89493
UnknownSummary
The Linux kernel ocfs2 module lacked validation of the rl_used and rl_count fields in the refcount block. A crafted or corrupted ocfs2 image with rl_used set to 0xffff causes an out-of-bounds read past the metadata block and a subsequent out-of-bounds memmove during a reflink (FICLONE) operation. Exploitation requires local access (CAP_SYS_ADMIN mounting a crafted image or raw write to the backing block device).
Risk Assessment
A local attacker with CAP_SYS_ADMIN can trigger out-of-bounds read and write in kernel memory, leading to a system crash (panic) or potentially kernel code execution. In multi-tenant environments or when mounting untrusted ocfs2 images, the risk of privilege escalation is real.
Recommendation
Update the Linux kernel to a version containing the fix that validates rl_count and rl_used in ocfs2_validate_refcount_block(). Until patched, avoid mounting untrusted or unverified ocfs2 images and restrict access to raw block devices.
Other vulnerabilities in Linux kernel (ocfs2)
See all- CVE-2026-89496Unknown
In the Linux kernel, the ocfs2 filesystem has a memory leak during copy-on-write operations triggered by copy_file_range() within the same filesystem. The issue was found by fuzzing and occurs because deallocations are not always run on copy-on-write completion, leading to unreferenced memory allocations.
- CVE-2026-89494Unknown
In the Linux kernel, the ocfs2 dlm_mig_lockres_handler trusted the num_locks and lockname_len fields from a DLM_MIG_LOCKRES message without validation. This led to an out-of-bounds read (BUG_ON panic) and a heap out-of-bounds write when copying the lock name into a fixed 32-byte object. Any node in the domain could trigger this.
- CVE-2026-89492Unknown
A vulnerability was found in the Linux kernel's ocfs2 module due to missing validation of directory-index entry counts when reading metadata. The functions ocfs2_validate_dx_leaf() and ocfs2_validate_dx_root() do not bound the de_num_used and de_count fields against the block capacity, allowing a crafted on-disk image to set them to 0xffff and cause an out-of-bounds read past the 4KB metadata block. The flaw is reachable from any path lookup, stat() or open() on an indexed directory once the image is mounted.
- CVE-2026-89490Unknown
In the Linux kernel, the ocfs2 function ocfs2_dir_foreach_blk_el() on 32-bit kernels incorrectly computed the directory position mask, clearing the high 32 bits of the position. When readdir() crossed the 4 GiB boundary, the position was reset, causing infinite re-enumeration of already-returned directory entries.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ocfs2: validate rl_used against rl_count in refcount block validator ocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array with: for (; i < le16_to_cpu(rb->rf_records.rl_used); i++) { rec = &rb->rf_records.rl_recs[i]; ... rl_recs[] lives in a single metadata block (4096 bytes on the common configuration), so its real capacity is fixed by ocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the 16-byte ocfs2_refcount_rec). rl_used and rl_count are both read directly off disk by ocfs2_validate_refcount_block() and are never checked against that capacity, nor against each other, before any refcount/reflink/CoW operation walks the array. A crafted (or corrupted) refcount block with rl_used == 0xffff makes the loop above walk far past the end of the block, dereferencing rl_recs[i] for i up to 65534. The resulting index is then handed to the sibling ocfs2_insert_refcount_rec(), whose insert-shift does: if (index < le16_to_cpu(rf_list->rl_used)) memmove(&rf_list->rl_recs[index + 1], &rf_list->rl_recs[index], (le16_to_cpu(rf_list->rl_used) - index) * sizeof(struct ocfs2_refcount_rec)); i.e. a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an offset already past the block. This is reachable from an ordinary reflink (FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent whose cpos sorts past every real record in the leaf forces the lookup to run off the end instead of returning early on a match. The attacker model is local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a raw write to the block device backing an already-mounted ocfs2 filesystem. ocfs2_validate_refcount_block() already validates the block's ECC, signature, rf_blkno and rf_fs_generation, but never rl_count/rl_used against the block's actual on-disk capacity. This is the same class of gap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes for the sibling extent-list header, which checks both the record capacity and the "used" bound before any code walks h_list.l_recs[]: if (le16_to_cpu(eb->h_list.l_count) != ocfs2_extent_recs_per_eb(sb)) { rc = ocfs2_error(...); goto bail; } if (le16_to_cpu(eb->h_list.l_next_free_rec) > le16_to_cpu(eb->h_list.l_count)) { rc = ocfs2_error(...); goto bail; } Add the equivalent pair of checks to ocfs2_validate_refcount_block(): reject a refcount block whose rl_count does not match the fixed per-block capacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used > rl_count. Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set, because in that case the same union bytes hold an ocfs2_extent_list (rf_list), not the refcount record list (rf_records) -- that layout is already validated separately by ocfs2_validate_extent_block() when the referenced extent block is read. This mirrors the existing "!(rb->rf_flags & OCFS2_REFCOUNT_TREE_FL)" guard used elsewhere in this file (e.g. ocfs2_get_refcount_rec()) to decide whether rf_records or rf_list is the live member of the union. With this in place, a forged rl_used/rl_count is caught at block validation time (ocfs2_error()), consistent with every other corruption check in this function, instead of driving an out-of-bounds read in ocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove() in ocfs2_insert_refcount_rec(). Verified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build: replaying the same reflink (FICLONE) reliably hit a KASAN report in __ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch, and triggers no report once ocfs2_validate_refcount_block() rejects the forged rl_used/rl_count.