xfs: forbid AG btrees with level == 0

commit d2a047f31e86941fa896e0e3271536d50aba415e upstream.

There is no such thing as a zero-level AG btree since even a single-node
zero-records btree has one level.  Btree cursor constructors read
cur_nlevels straight from disk and then access things like
cur_bufs[cur_nlevels - 1] which is /really/ bad if cur_nlevels is zero!
Therefore, strengthen the verifiers to prevent this possibility.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 15 insertions, 4 deletions

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index effb64cf714f..5050056a0b06 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2455,12 +2455,15 @@ xfs_agf_verify(
               be32_to_cpu(agf->agf_flcount) <= XFS_AGFL_SIZE(mp)))
                 return false;
 
-        if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS ||
+        if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) < 1 ||
+            be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) < 1 ||
+            be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS ||
             be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) > XFS_BTREE_MAXLEVELS)
                 return false;
 
         if (xfs_sb_version_hasrmapbt(&mp->m_sb) &&
-            be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]) > XFS_BTREE_MAXLEVELS)
+            (be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]) < 1 ||
+             be32_to_cpu(agf->agf_levels[XFS_BTNUM_RMAP]) > XFS_BTREE_MAXLEVELS))
                 return false;
 
         /*
@@ -2477,7 +2480,8 @@ xfs_agf_verify(
                 return false;
 
         if (xfs_sb_version_hasreflink(&mp->m_sb) &&
-            be32_to_cpu(agf->agf_refcount_level) > XFS_BTREE_MAXLEVELS)
+            (be32_to_cpu(agf->agf_refcount_level) < 1 ||
+             be32_to_cpu(agf->agf_refcount_level) > XFS_BTREE_MAXLEVELS))
                 return false;
 
         return true;;
diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index c482b9716347..d45c03779dae 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -2510,8 +2510,15 @@ xfs_agi_verify(
         if (!XFS_AGI_GOOD_VERSION(be32_to_cpu(agi->agi_versionnum)))
                 return false;
 
-        if (be32_to_cpu(agi->agi_level) > XFS_BTREE_MAXLEVELS)
+        if (be32_to_cpu(agi->agi_level) < 1 ||
+            be32_to_cpu(agi->agi_level) > XFS_BTREE_MAXLEVELS)
                 return false;
+
+        if (xfs_sb_version_hasfinobt(&mp->m_sb) &&
+            (be32_to_cpu(agi->agi_free_level) < 1 ||
+             be32_to_cpu(agi->agi_free_level) > XFS_BTREE_MAXLEVELS))
+                return false;
+
         /*
          * during growfs operations, the perag is not fully initialised,
          * so we can't use it for any useful checking. growfs ensures we can't