Bug 2493754 (CVE-2026-53320)

Summary: CVE-2026-53320 kernel: nilfs2: reject zero bd_oblocknr in nilfs_ioctl_mark_blocks_dirty()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `nilfs2` filesystem. A local attacker could exploit this vulnerability by sending a specially crafted input/output control (ioctl) request to the `nilfs_ioctl_mark_blocks_dirty()` function. By providing a zero block number, the attacker can bypass a critical dead block check, causing the system to attempt operations on a non-existent block. This ultimately leads to a system crash, resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-06-26 21:05:16 UTC 
In the Linux kernel, the following vulnerability has been resolved:

nilfs2: reject zero bd_oblocknr in nilfs_ioctl_mark_blocks_dirty()

nilfs_ioctl_mark_blocks_dirty() uses bd_oblocknr to detect dead blocks
by comparing it with the current block number bd_blocknr. If they differ,
the block is considered dead and skipped.

However, bd_oblocknr should never be 0 since block 0 typically stores the
primary superblock and is never a valid GC target block. A corrupted ioctl
request with bd_oblocknr set to 0 causes the comparison to incorrectly
match when the lookup returns -ENOENT and sets bd_blocknr to 0, bypassing
the dead block check and calling nilfs_bmap_mark() on a non-existent
block. This causes nilfs_btree_do_lookup() to return -ENOENT, triggering
the WARN_ON(ret == -ENOENT).

Fix this by rejecting ioctl requests with bd_oblocknr set to 0 at the
beginning of each iteration.

[ryusuke: slightly modified the commit message and comments for accuracy]
Comment 1 Mauro Matteo Cascella 2026-06-29 08:38:58 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026062622-CVE-2026-53320-a56a@gregkh/T