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CVE-2026-89640: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-11 · updated 2026-10-30

Description

In the Linux kernel, the following vulnerability has been resolved: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0 With len == 0 (clone to EOF), the effective length is computed as: len = src_inode->i_size - off; If off > i_size, this is a negative loff_t, corrupting the ByteCount in the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range in filemap_write_and_wait_range(). The existing off >= i_size check fires only after the ioctl has already been sent. Snapshot i_size_read() once for both the bounds check and the length calculation, eliminating the TOCTOU and 32-bit torn-read risk. Reject off > src_size with -EINVAL. Treat off == src_size as a no-op, consistent with __generic_remap_file_range_prep().

Affected products

• Linux: 4.5 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/2c6eede83b3de1268db92c7e49741761c954aa26
• https://git.kernel.org/stable/c/6c322f5cf7476ded7a9a20f7be72462065a03c68
• https://git.kernel.org/stable/c/7f62817fe049b0f3652518c1ba72631ec1e0a322
• https://git.kernel.org/stable/c/b057ca17b656345d04669cb87f2aff9b31d873db
• https://git.kernel.org/stable/c/b098f5e5858797827666e6cd73033f52fc39b5f6
• https://git.kernel.org/stable/c/c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028
• https://git.kernel.org/stable/c/ce813e5eebf46851e872ce59bdc34dc5dd4e29a4
• https://git.kernel.org/stable/c/f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4

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