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CVE-2025-40205 is a Linux kernel memory-corruption vulnerability in the Btrfs filesystem export code, specifically in btrfs_encode_fh() in fs/btrfs/export.c. The flaw arises from incorrect file-handle size accounting across the three cases handled by the function. Before writing to the file handle buffer, the function reported only the sizes corresponding to non-connectable or connectable handles, but in the case where a parent exists and the parent root ID differs from the inode root ID, it writes the larger connectable-root form. If *max_len is smaller than the actual size needed for that case, the function performs an 8-byte out-of-bounds write when storing the parent root object ID. The issue is described as not easily triggerable, but it constitutes a longstanding potential kernel memory corruption bug.
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A Linux kernel Btrfs vulnerability in btrfs_encode_fh() that can cause an out-of-bounds write due to incorrect file handle size accounting, leading to potential memory corruption.
A Linux kernel Btrfs vulnerability in btrfs_encode_fh() that can cause an 8-byte out-of-bounds write due to incorrect size handling across file handle encoding cases, leading to potential memory corruption.
A potential out-of-bounds write in the Linux kernel Btrfs filesystem's btrfs_encode_fh() implementation, where the first size calculation can return a smaller handle length than the second call writes when parent and inode root IDs differ, causing an 8-byte kernel out-of-bounds write.
A potential out-of-bounds write in the Linux kernel Btrfs file system's btrfs_encode_fh() file handle implementation, where insufficiently sized allocation can be followed by a larger write when parent and inode root IDs differ.
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