[PATCH] f2fs: bound i_inline_xattr_size for non-inline-xattr inodes

[Bryam Vargas via B4 Relay]

From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

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.

Fixes: 6afc662e68b5 ("f2fs: support flexible inline xattr size")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
---
 fs/f2fs/inode.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index c6dcda447882..5c0f62190875 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -324,9 +324,9 @@ static bool sanity_check_inode(struct inode *inode, struct folio *node_folio)
 	}
 
 	if (f2fs_sb_has_flexible_inline_xattr(sbi) &&
-		f2fs_has_inline_xattr(inode) &&
-		(fi->i_inline_xattr_size < MIN_INLINE_XATTR_SIZE ||
-		fi->i_inline_xattr_size > MAX_INLINE_XATTR_SIZE)) {
+		(fi->i_inline_xattr_size > MAX_INLINE_XATTR_SIZE ||
+		(f2fs_has_inline_xattr(inode) &&
+		fi->i_inline_xattr_size < MIN_INLINE_XATTR_SIZE))) {
 		f2fs_warn(sbi, "%s: inode (ino=%llx) has corrupted i_inline_xattr_size: %d, min: %zu, max: %lu",
 			  __func__, inode->i_ino, fi->i_inline_xattr_size,
 			  MIN_INLINE_XATTR_SIZE, MAX_INLINE_XATTR_SIZE);

---
base-commit: 8e65320d91cdc3b241d4b94855c88459b91abf66
change-id: 20260611-b4-disp-155e8807-81fd7e4d00ac

Best regards,
-- 
Bryam Vargas <hexlabsecurity@xxxxxxxxx>