[PATCH 4/4] xfs: validate v5 feature fields

Dave Chinner
2022-05-02T08:20:45Z

From: Dave Chinner <dchinner@redhat.com>

Because stupid dumb fuzzers.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/libxfs/xfs_sb.c | 67 +++++++++++++++++++++++++++++++++++-------
1 file changed, 57 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index ec6eec5c0e02..d1afe0d43d7f 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -30,6 +30,46 @@
* Physical superblock buffer manipulations. Shared with libxfs in userspace.
*/

+/*
+ * Validate all the compulsory V4 feature bits are set on a V5 filesystem.
+ */
+bool
+xfs_sb_validate_v5_features(
+ struct xfs_sb *sbp)
+{
+ /* We must not have any unknown V4 feature bits set */
+ if (sbp->sb_versionnum & ~XFS_SB_VERSION_OKBITS)
+ return false;
+
+ /*
+ * The CRC bit is considered an invalid V4 flag, so we have to add it
+ * manually to the OKBITS mask.
+ */
+ if (sbp->sb_features2 & ~(XFS_SB_VERSION2_OKBITS |
+ XFS_SB_VERSION2_CRCBIT))
+ return false;
+
+ /* Now check all the required V4 feature flags are set. */
+
+#define V5_VERS_FLAGS (XFS_SB_VERSION_NLINKBIT | \
+ XFS_SB_VERSION_ALIGNBIT | \
+ XFS_SB_VERSION_LOGV2BIT | \
+ XFS_SB_VERSION_EXTFLGBIT | \
+ XFS_SB_VERSION_DIRV2BIT | \
+ XFS_SB_VERSION_MOREBITSBIT)
+
+#define V5_FEAT_FLAGS (XFS_SB_VERSION2_LAZYSBCOUNTBIT | \
+ XFS_SB_VERSION2_ATTR2BIT | \
+ XFS_SB_VERSION2_PROJID32BIT | \
+ XFS_SB_VERSION2_CRCBIT)
+
+ if ((sbp->sb_versionnum & V5_VERS_FLAGS) != V5_VERS_FLAGS)
+ return false;
+ if ((sbp->sb_features2 & V5_FEAT_FLAGS) != V5_FEAT_FLAGS)
+ return false;
+ return true;
+}
+
/*
* We support all XFS versions newer than a v4 superblock with V2 directories.
*/
@@ -37,9 +77,19 @@ bool
xfs_sb_good_version(
struct xfs_sb *sbp)
{
- /* all v5 filesystems are supported */
+ /*
+ * All v5 filesystems are supported, but we must check that all the
+ * required v4 feature flags are enabled correctly as the code checks
+ * those flags and not for v5 support.
+ */
if (xfs_sb_is_v5(sbp))
- return true;
+ return xfs_sb_validate_v5_features(sbp);
+
+ /* We must not have any unknown v4 feature bits set */
+ if ((sbp->sb_versionnum & ~XFS_SB_VERSION_OKBITS) ||
+ ((sbp->sb_versionnum & XFS_SB_VERSION_MOREBITSBIT) &&
+ (sbp->sb_features2 & ~XFS_SB_VERSION2_OKBITS)))
+ return false;

/* versions prior to v4 are not supported */
if (XFS_SB_VERSION_NUM(sbp) < XFS_SB_VERSION_4)
@@ -51,12 +101,6 @@ xfs_sb_good_version(
if (!(sbp->sb_versionnum & XFS_SB_VERSION_EXTFLGBIT))
return false;

- /* And must not have any unknown v4 feature bits set */
- if ((sbp->sb_versionnum & ~XFS_SB_VERSION_OKBITS) ||
- ((sbp->sb_versionnum & XFS_SB_VERSION_MOREBITSBIT) &&
- (sbp->sb_features2 & ~XFS_SB_VERSION2_OKBITS)))
- return false;
-
/* It's a supported v4 filesystem */
return true;
}
@@ -267,12 +311,15 @@ xfs_validate_sb_common(
bool has_dalign;

if (!xfs_verify_magic(bp, dsb->sb_magicnum)) {
- xfs_warn(mp, "bad magic number");
+ xfs_warn(mp,
+"Superblock has bad magic number 0x%x. Not an XFS filesystem?",
+ be32_to_cpu(dsb->sb_magicnum));
return -EWRONGFS;
}

if (!xfs_sb_good_version(sbp)) {
- xfs_warn(mp, "bad version");
+ xfs_warn(mp,
+"Superblock has unknown features enabled or corrupted feature masks.");
return -EWRONGFS;
}

--
2.35.1