[PATCH v3 2/4] ocfs2: validate suballoc bit during inode read

[Joseph Qi <joseph.qi@linux.alibaba.com>]

i_suballoc_bit of a dinode is currently not validated at all.  A
corrupted dinode can carry an abnormally large i_suballoc_bit, which
bypasses ocfs2_validate_inode_block().  When the inode is deleted,
ocfs2_remove_inode() calls ocfs2_free_dinode(), which passes the
unvalidated bit to _ocfs2_free_suballoc_bits() and triggers
BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl)).

A suballocator block group bitmap is contained in a single block and
starts after the group descriptor header, so a valid suballoc bit must
be smaller than the number of bits fitting in the remaining space.
Reject oversized i_suballoc_bit values during dinode validation.  The
bound is derived from ocfs2_group_bitmap_size() so it is also tight
when discontig_bg caps the suballocator bitmap at
OCFS2_MAX_BG_BITMAP_SIZE.

Note the above check alone is not sufficient since the freeing path
compares the bit against ocfs2_bits_per_group(), which is derived from
cl_cpg/cl_bpc of the allocator dinode that is not validated against
the actual group capacity and can be artificially smaller on a
corrupted image.  Convert this BUG_ON in _ocfs2_free_suballoc_bits()
to ocfs2_error() as well.

Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
---
 fs/ocfs2/inode.c    | 16 ++++++++++++++++
 fs/ocfs2/ocfs2.h    | 12 ++++++++++++
 fs/ocfs2/suballoc.c | 18 +++++++++++++++---
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 9228d6ef23c2..92f3450010fb 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1547,6 +1547,22 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	/*
+	 * A suballocator block group bitmap is contained in a single block
+	 * and starts after the group descriptor header, so a valid suballoc
+	 * bit can never exceed ocfs2_suballoc_bits_per_block().  Otherwise
+	 * deleting the inode will pass the oversized bit to
+	 * _ocfs2_free_suballoc_bits() via ocfs2_free_dinode() and trigger
+	 * BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl)), since any
+	 * group holds at most ocfs2_suballoc_bits_per_block() bits.
+	 */
+	if (le16_to_cpu(di->i_suballoc_bit) >= ocfs2_suballoc_bits_per_block(sb)) {
+		rc = ocfs2_error(sb, "Invalid dinode %llu: suballoc bit %u\n",
+				 (unsigned long long)bh->b_blocknr,
+				 le16_to_cpu(di->i_suballoc_bit));
+		goto bail;
+	}
+
 	if ((le32_to_cpu(di->i_flags) & OCFS2_ORPHANED_FL) &&
 	    le16_to_cpu(di->i_orphaned_slot) >= OCFS2_SB(sb)->max_slots) {
 		rc = ocfs2_error(sb, "Invalid dinode %llu: orphaned slot %u\n",
diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index b747cdec1787..e3bb3cc0b25a 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -593,6 +593,18 @@ static inline int ocfs2_supports_discontig_bg(struct ocfs2_super *osb)
 	return 0;
 }
 
+/*
+ * A suballocator block group bitmap starts right after the group
+ * descriptor header, so a suballoc bit can never exceed this number
+ * of bits.  Derive it from ocfs2_group_bitmap_size() which also caps
+ * it at OCFS2_MAX_BG_BITMAP_SIZE when discontig_bg is enabled.
+ */
+static inline u32 ocfs2_suballoc_bits_per_block(struct super_block *sb)
+{
+	return ocfs2_group_bitmap_size(sb, 1,
+				       OCFS2_SB(sb)->s_feature_incompat) * 8;
+}
+
 static inline unsigned int ocfs2_link_max(struct ocfs2_super *osb)
 {
 	if (ocfs2_supports_indexed_dirs(osb))
diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 453b56be9624..ce22d0c3d287 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -3040,10 +3040,22 @@ static int _ocfs2_free_suballoc_bits(handle_t *handle,
 	/* The alloc_bh comes from ocfs2_free_dinode() or
 	 * ocfs2_free_clusters().  The callers have all locked the
 	 * allocator and gotten alloc_bh from the lock call.  This
-	 * validates the dinode buffer.  Any corruption that has happened
-	 * is a code bug. */
+	 * validates the dinode buffer. */
 	BUG_ON(!OCFS2_IS_VALID_DINODE(fe));
-	BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl));
+
+	/*
+	 * ocfs2_bits_per_group() is derived from cl_cpg and cl_bpc of the
+	 * allocator dinode, which are not validated against the volume
+	 * geometry.  A corrupted image can carry a suballoc bit beyond it,
+	 * so error out instead of crashing.
+	 */
+	if ((count + start_bit) > ocfs2_bits_per_group(cl)) {
+		return ocfs2_error(alloc_inode->i_sb,
+				   "Allocator #%llu: freeing bits %u+%u exceeds bits per group %u\n",
+				   (unsigned long long)le64_to_cpu(fe->i_blkno),
+				   count, start_bit,
+				   ocfs2_bits_per_group(cl));
+	}
 
 	trace_ocfs2_free_suballoc_bits(
 		(unsigned long long)OCFS2_I(alloc_inode)->ip_blkno,
-- 
2.39.3