[PATCH v2 2/3] ocfs2: reject dinodes whose i_rdev disagrees with the file type

[Michael Bommarito <michael.bommarito@gmail.com>]

id1.dev1.i_rdev is the device-number arm of the ocfs2_dinode id1 union.
It is only meaningful for character and block device inodes. For any
other user-visible file type the on-disk value must be zero.

ocfs2_populate_inode() currently copies id1.dev1.i_rdev into
inode->i_rdev before the S_IFMT switch decides whether the inode is a
special file. A non-device inode with a non-zero i_rdev can therefore
publish stale or attacker-controlled device state into the in-core inode.

System inodes legitimately use other arms of the same union, so keep
the cross-check restricted to non-system inodes. Factor that predicate
into a helper and use it in both the normal validator and online
filecheck path; filecheck reports the malformed dinode through
OCFS2_FILECHECK_ERR_INVALIDINO instead of ocfs2_error().

Fixes: b657c95c1108 ("ocfs2: Wrap inode block reads in a dedicated function.")
Cc: stable@vger.kernel.org
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Assisted-by: Claude:claude-opus-4-7
---
 fs/ocfs2/inode.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index e149ccbdc03ce..992980ea98046 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -72,6 +72,16 @@ static bool ocfs2_valid_inode_mode(umode_t mode)
 	return fs_umode_to_ftype(mode) != FT_UNKNOWN;
 }
 
+static bool ocfs2_dinode_has_unexpected_rdev(struct ocfs2_dinode *di)
+{
+	umode_t mode = le16_to_cpu(di->i_mode);
+
+	if (le32_to_cpu(di->i_flags) & OCFS2_SYSTEM_FL)
+		return false;
+
+	return !S_ISCHR(mode) && !S_ISBLK(mode) && di->id1.dev1.i_rdev != 0;
+}
+
 void ocfs2_set_inode_flags(struct inode *inode)
 {
 	unsigned int flags = OCFS2_I(inode)->ip_attr;
@@ -1518,6 +1528,41 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	/*
+	 * id1.dev1.i_rdev is the device-number arm of the id1 union and
+	 * is only meaningful for character and block device inodes.  For
+	 * any other regular user-visible file type the on-disk value
+	 * must be zero.  ocfs2_populate_inode() currently runs
+	 *
+	 *     inode->i_rdev = huge_decode_dev(le64_to_cpu(fe->id1.dev1.i_rdev));
+	 *
+	 * unconditionally, before the S_IFMT switch decides whether the
+	 * inode is a special file.  As a result, an i_rdev value present
+	 * on a non-device inode is silently published into the in-core
+	 * inode; a subsequent forced re-read or in-core mode mutation
+	 * (cluster peer with raw write access to the shared LUN,
+	 * on-disk corruption, or a separately forged dinode) can then
+	 * expose the attacker-controlled device number to
+	 * init_special_inode() without ever showing an unusual i_mode
+	 * at validation time.
+	 *
+	 * System inodes (OCFS2_SYSTEM_FL) legitimately use the bitmap1
+	 * and journal1 arms of the same union (allocator i_used /
+	 * i_total counters and the journal ij_flags /
+	 * ij_recovery_generation pair); those bytes are not an i_rdev
+	 * and must not be checked here.  Restrict the cross-check to
+	 * non-system inodes, which is the full attacker-controllable
+	 * surface.
+	 */
+	if (ocfs2_dinode_has_unexpected_rdev(di)) {
+		rc = ocfs2_error(sb,
+				 "Invalid dinode #%llu: non-device mode 0%o with i_rdev %llu\n",
+				 (unsigned long long)bh->b_blocknr,
+				 le16_to_cpu(di->i_mode),
+				 (unsigned long long)le64_to_cpu(di->id1.dev1.i_rdev));
+		goto bail;
+	}
+
 	if (le16_to_cpu(di->i_dyn_features) & OCFS2_INLINE_DATA_FL) {
 		struct ocfs2_inline_data *data = &di->id2.i_data;
 
@@ -1657,6 +1702,16 @@ static int ocfs2_filecheck_validate_inode_block(struct super_block *sb,
 		     (unsigned long long)bh->b_blocknr,
 		     le16_to_cpu(di->i_mode));
 		rc = -OCFS2_FILECHECK_ERR_INVALIDINO;
+		goto bail;
+	}
+
+	if (ocfs2_dinode_has_unexpected_rdev(di)) {
+		mlog(ML_ERROR,
+		     "Filecheck: invalid dinode #%llu: non-device mode 0%o with i_rdev %llu\n",
+		     (unsigned long long)bh->b_blocknr,
+		     le16_to_cpu(di->i_mode),
+		     (unsigned long long)le64_to_cpu(di->id1.dev1.i_rdev));
+		rc = -OCFS2_FILECHECK_ERR_INVALIDINO;
 	}
 
 bail:
-- 
2.53.0