Merge tag 'fix-rtmount-overflows-6.8_2023-12-06' of...

Merge tag 'fix-rtmount-overflows-6.8_2023-12-06' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-6.8-mergeA

xfs: fix realtime geometry integer overflows

While reading through the realtime geometry support code in xfsprogs, I
noticed a discrepancy between the sb_rextslog computation used when
writing out the superblock during mkfs and the validation code used in
xfs_repair.  This discrepancy would lead to system failure for a runt rt
volume having more than 1 rt block but zero rt extents in length.  Most
people aren't going to configure a 1M extent size for their 360k rt
floppy disk volume, but I did!

In the process of studying that code, it occurred to me that there is a
second bug in the computation -- the use of highbit32 for a 64-bit
value means that the upper 32 bits are not considered in the search for
a high bit.  This causes the creation of a realtime summary file that is
the wrong length.  If rextents is a multiple of U32_MAX then this will
appear to work fine because highbit32 returns -1 for an input of 0; but
for all other cases the rt summary is undersized, leading to failures.

Fix the first problem by standardizing the computation with a helper in
libxfs; and the second problem by correcting the computation.  This will
cause any existing rt volumes larger than 2^32 blocks to fail validation
but they probably were already crashing anyway.

This has been lightly tested with fstests.  Enjoy!
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

* tag 'fix-rtmount-overflows-6.8_2023-12-06' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: don't allow overly small or large realtime volumes
  xfs: fix 32-bit truncation in xfs_compute_rextslog
  xfs: make rextslog computation consistent with mkfs

fs/xfs/libxfs/xfs_rtbitmap.c

@@ -1130,6 +1130,20 @@ xfs_rtbitmap_blockcount(
 	return howmany_64(rtextents, NBBY * mp->m_sb.sb_blocksize);
 }
 
+/*
+ * Compute the maximum level number of the realtime summary file, as defined by
+ * mkfs.  The historic use of highbit32 on a 64-bit quantity prohibited correct
+ * use of rt volumes with more than 2^32 extents.
+ */
+uint8_t
+xfs_compute_rextslog(
+	xfs_rtbxlen_t		rtextents)
+{
+	if (!rtextents)
+		return 0;
+	return xfs_highbit64(rtextents);
+}
+
 /*
  * Compute the number of rtbitmap words needed to populate every block of a
  * bitmap that is large enough to track the given number of rt extents.

fs/xfs/libxfs/xfs_rtbitmap.h

@@ -351,6 +351,20 @@ xfs_rtfree_extent(
 int xfs_rtfree_blocks(struct xfs_trans *tp, xfs_fsblock_t rtbno,
 		xfs_filblks_t rtlen);
 
+uint8_t xfs_compute_rextslog(xfs_rtbxlen_t rtextents);
+
+/* Do we support an rt volume having this number of rtextents? */
+static inline bool
+xfs_validate_rtextents(
+	xfs_rtbxlen_t		rtextents)
+{
+	/* No runt rt volumes */
+	if (rtextents == 0)
+		return false;
+
+	return true;
+}
+
 xfs_filblks_t xfs_rtbitmap_blockcount(struct xfs_mount *mp, xfs_rtbxlen_t
 		rtextents);
 unsigned long long xfs_rtbitmap_wordcount(struct xfs_mount *mp,
@@ -369,6 +383,8 @@ unsigned long long xfs_rtsummary_wordcount(struct xfs_mount *mp,
 # define xfs_rtsummary_read_buf(a,b)			(-ENOSYS)
 # define xfs_rtbuf_cache_relse(a)			(0)
 # define xfs_rtalloc_extent_is_free(m,t,s,l,i)		(-ENOSYS)
+# define xfs_compute_rextslog(rtx)			(0)
+# define xfs_validate_rtextents(rtx)			(false)
 static inline xfs_filblks_t
 xfs_rtbitmap_blockcount(struct xfs_mount *mp, xfs_rtbxlen_t rtextents)
 {

fs/xfs/libxfs/xfs_sb.c

@@ -25,6 +25,7 @@
 #include "xfs_da_format.h"
 #include "xfs_health.h"
 #include "xfs_ag.h"
+#include "xfs_rtbitmap.h"
 
 /*
  * Physical superblock buffer manipulations. Shared with libxfs in userspace.
@@ -508,8 +509,9 @@ xfs_validate_sb_common(
 		rbmblocks = howmany_64(sbp->sb_rextents,
 				       NBBY * sbp->sb_blocksize);
 
-		if (sbp->sb_rextents != rexts ||
-		    sbp->sb_rextslog != xfs_highbit32(sbp->sb_rextents) ||
+		if (!xfs_validate_rtextents(rexts) ||
+		    sbp->sb_rextents != rexts ||
+		    sbp->sb_rextslog != xfs_compute_rextslog(rexts) ||
 		    sbp->sb_rbmblocks != rbmblocks) {
 			xfs_notice(mp,
 				"realtime geometry sanity check failed");

fs/xfs/xfs_rtalloc.c

@@ -963,8 +963,10 @@ xfs_growfs_rt(
 	 */
 	nrextents = nrblocks;
 	do_div(nrextents, in->extsize);
+	if (!xfs_validate_rtextents(nrextents))
+		return -EINVAL;
 	nrbmblocks = xfs_rtbitmap_blockcount(mp, nrextents);
-	nrextslog = xfs_highbit32(nrextents);
+	nrextslog = xfs_compute_rextslog(nrextents);
 	nrsumlevels = nrextslog + 1;
 	nrsumblocks = xfs_rtsummary_blockcount(mp, nrsumlevels, nrbmblocks);
 	nrsumsize = XFS_FSB_TO_B(mp, nrsumblocks);
@@ -1031,7 +1033,7 @@ xfs_growfs_rt(
 		nsbp->sb_rblocks = min(nrblocks, nrblocks_step);
 		nsbp->sb_rextents = xfs_rtb_to_rtx(nmp, nsbp->sb_rblocks);
 		ASSERT(nsbp->sb_rextents != 0);
-		nsbp->sb_rextslog = xfs_highbit32(nsbp->sb_rextents);
+		nsbp->sb_rextslog = xfs_compute_rextslog(nsbp->sb_rextents);
 		nrsumlevels = nmp->m_rsumlevels = nsbp->sb_rextslog + 1;
 		nrsumblocks = xfs_rtsummary_blockcount(mp, nrsumlevels,
 				nsbp->sb_rbmblocks);