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 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.
