[PATCH v2 1/4] ocfs2: restrict OCFS2_INVALID_SLOT suballoc slot to system inodes

[Joseph Qi]

ocfs2_validate_inode_block() currently permits i_suballoc_slot to be
OCFS2_INVALID_SLOT for any dinode.  Only system inodes created by
mkfs.ocfs2 are allocated from the global allocator and thus
legitimately carry this value; regular inodes are always allocated
from a per-slot suballocator and hence must have a valid slot.

If a corrupted regular inode with OCFS2_INVALID_SLOT is accepted,
ocfs2_remove_inode() will pass the slot to ocfs2_get_system_file_inode()
and get_local_system_inode() will hit BUG_ON(slot == OCFS2_INVALID_SLOT)
when the inode is deleted.  This can be triggered by an unprivileged
user unlinking such a corrupted file.

Reject OCFS2_INVALID_SLOT for non-system dinodes during validation,
while still accepting it for system inodes.  Note that a crafted dinode
carrying OCFS2_SYSTEM_FL passes the check above, yet a plain lookup of
it still used to BUG() in ocfs2_read_locked_inode() ("system file state
is ambiguous").  Since i_flags comes from disk, handle that mismatch
with ocfs2_error() instead of BUG_ON() as well.

Fixes: fe7a283b3916 ("ocfs2: add suballoc slot check in ocfs2_validate_inode_block()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
---
 fs/ocfs2/inode.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 180107a11046..9228d6ef23c2 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -638,14 +638,18 @@ static int ocfs2_read_locked_inode(struct inode *inode,
 	fe = (struct ocfs2_dinode *) bh->b_data;
 
 	/*
-	 * This is a code bug. Right now the caller needs to
-	 * understand whether it is asking for a system file inode or
-	 * not so the proper lock names can be built.
+	 * The caller must know whether it is asking for a system file inode
+	 * or not so the proper lock names can be built.  Since i_flags comes
+	 * from disk, a mismatch is filesystem corruption instead of a code
+	 * bug, so handle it with ocfs2_error() rather than BUG_ON().
 	 */
-	mlog_bug_on_msg(!!(fe->i_flags & cpu_to_le32(OCFS2_SYSTEM_FL)) !=
-			!!(args->fi_flags & OCFS2_FI_FLAG_SYSFILE),
-			"Inode %llu: system file state is ambiguous\n",
-			(unsigned long long)args->fi_blkno);
+	if (!!(fe->i_flags & cpu_to_le32(OCFS2_SYSTEM_FL)) !=
+	    !!(args->fi_flags & OCFS2_FI_FLAG_SYSFILE)) {
+		status = ocfs2_error(osb->sb,
+				     "Inode %llu: system file state is ambiguous\n",
+				     (unsigned long long)args->fi_blkno);
+		goto bail;
+	}
 
 	if (S_ISCHR(le16_to_cpu(fe->i_mode)) ||
 	    S_ISBLK(le16_to_cpu(fe->i_mode)))
@@ -1520,8 +1524,23 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
-	if (le16_to_cpu(di->i_suballoc_slot) != (u16)OCFS2_INVALID_SLOT &&
-	    (u32)le16_to_cpu(di->i_suballoc_slot) > OCFS2_SB(sb)->max_slots - 1) {
+	/*
+	 * Only system inodes created by mkfs.ocfs2 are allocated from the
+	 * global allocator and thus legitimately carry OCFS2_INVALID_SLOT.
+	 * Regular inodes are always allocated from a per-slot suballocator.
+	 * If a regular inode with OCFS2_INVALID_SLOT was accepted here,
+	 * deleting it would pass the slot to get_local_system_inode() via
+	 * ocfs2_remove_inode() and trigger BUG_ON(slot == OCFS2_INVALID_SLOT).
+	 */
+	if (le16_to_cpu(di->i_suballoc_slot) == (u16)OCFS2_INVALID_SLOT) {
+		if (!(le32_to_cpu(di->i_flags) & OCFS2_SYSTEM_FL)) {
+			rc = ocfs2_error(sb,
+					 "Invalid dinode %llu: suballoc slot %u for non-system inode\n",
+					 (unsigned long long)bh->b_blocknr,
+					 le16_to_cpu(di->i_suballoc_slot));
+			goto bail;
+		}
+	} else if ((u32)le16_to_cpu(di->i_suballoc_slot) > OCFS2_SB(sb)->max_slots - 1) {
 		rc = ocfs2_error(sb, "Invalid dinode %llu: suballoc slot %u\n",
 				 (unsigned long long)bh->b_blocknr,
 				 le16_to_cpu(di->i_suballoc_slot));
-- 
2.39.3