[PATCH v3 1/5] xfs: check sb_agblocks and sb_agblklog when validating superblock

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

Currently, we don't check sb_agblocks or sb_agblklog when we validate
the superblock, which means that we can fuzz garbage values into those
values and the mount succeeds.  This leads to all sorts of UBSAN
warnings in xfs/350 since we can then coerce other parts of xfs into
shifting by ridiculously large values.

Once we've validated agblocks, make sure the agcount makes sense.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v3: also check that dblocks/agcount/agblocks make sense
v2: simplify ag min/max size definitions
---
 fs/xfs/libxfs/xfs_fs.h |    7 +++++++
 fs/xfs/libxfs/xfs_sb.c |   14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index fc4386a..1de8555 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -233,6 +233,13 @@ typedef struct xfs_fsop_resblks {
 #define XFS_MAX_LOG_BLOCKS	(1024 * 1024ULL)
 #define XFS_MIN_LOG_BYTES	(10 * 1024 * 1024ULL)
 
+/*
+ * Limits on sb_agblocks/sb_agblklog -- mkfs won't format AGs smaller than
+ * 16MB or larger than 1TB.
+ */
+#define XFS_MIN_AG_BYTES	(1ULL << 24)	/* 16 MB */
+#define XFS_MAX_AG_BYTES	(1ULL << 40)	/* 1 TB */
+
 /* keep the maximum size under 2^31 by a small amount */
 #define XFS_MAX_LOG_BYTES \
 	((2 * 1024 * 1024 * 1024ULL) - XFS_MIN_LOG_BYTES)
diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
index 08e44a0..e2b82d7 100644
--- a/fs/xfs/libxfs/xfs_sb.c
+++ b/fs/xfs/libxfs/xfs_sb.c
@@ -119,6 +119,9 @@ xfs_mount_validate_sb(
 	bool		check_inprogress,
 	bool		check_version)
 {
+	u32		agcount = 0;
+	u32		rem;
+
 	if (sbp->sb_magicnum != XFS_SB_MAGIC) {
 		xfs_warn(mp, "bad magic number");
 		return -EWRONGFS;
@@ -229,6 +232,13 @@ xfs_mount_validate_sb(
 		return -EINVAL;
 	}
 
+	/* Compute agcount for this number of dblocks and agblocks */
+	if (sbp->sb_agblocks) {
+		agcount = div_u64_rem(sbp->sb_dblocks, sbp->sb_agblocks, &rem);
+		if (rem)
+			agcount++;
+	}
+
 	/*
 	 * More sanity checking.  Most of these were stolen directly from
 	 * xfs_repair.
@@ -253,6 +263,10 @@ xfs_mount_validate_sb(
 	    sbp->sb_inodesize != (1 << sbp->sb_inodelog)		||
 	    sbp->sb_logsunit > XLOG_MAX_RECORD_BSIZE			||
 	    sbp->sb_inopblock != howmany(sbp->sb_blocksize,sbp->sb_inodesize) ||
+	    XFS_FSB_TO_B(mp, sbp->sb_agblocks) < XFS_MIN_AG_BYTES	||
+	    XFS_FSB_TO_B(mp, sbp->sb_agblocks) > XFS_MAX_AG_BYTES	||
+	    sbp->sb_agblklog != xfs_highbit32(sbp->sb_agblocks - 1) + 1	||
+	    agcount == 0 || agcount != sbp->sb_agcount			||
 	    (sbp->sb_blocklog - sbp->sb_inodelog != sbp->sb_inopblog)	||
 	    (sbp->sb_rextsize * sbp->sb_blocksize > XFS_MAX_RTEXTSIZE)	||
 	    (sbp->sb_rextsize * sbp->sb_blocksize < XFS_MIN_RTEXTSIZE)	||