[PATCH 2/2] ocfs2: validate DIO orphan slot during inode read

[ZhengYuan Huang <gality369@gmail.com>]

[BUG]
A corrupted append-DIO dinode (high byte at offset 0xa1 
corrupted from 0 to 1) can carry an i_dio_orphaned_slot
outside the mounted filesystem slot range and trigger a 
use-after-free error:

BUG: KASAN: slab-use-after-free in ocfs2_get_system_file_inode+0x780/0x820 fs/ocfs2/sysfile.c:102
Read of size 8 at addr ffff88800b767c00 by task kworker/u8:3/85
Call Trace:
 ...
 ocfs2_get_system_file_inode+0x780/0x820 fs/ocfs2/sysfile.c:102
 ocfs2_wipe_inode+0x292/0xf70 fs/ocfs2/inode.c:840
 ocfs2_delete_inode fs/ocfs2/inode.c:1155 [inline]
 ocfs2_evict_inode+0x6c9/0x1170 fs/ocfs2/inode.c:1295
 evict+0x38e/0x8f0 fs/inode.c:810
 iput_final fs/inode.c:1914 [inline]
 iput fs/inode.c:1966 [inline]
 iput+0x55b/0x8b0 fs/inode.c:1926
 ocfs2_recover_orphans+0x610/0xe40 fs/ocfs2/journal.c:2374
 ocfs2_complete_recovery+0x5af/0xd00 fs/ocfs2/journal.c:1373
 ...

[CAUSE]
ocfs2_del_inode_from_orphan() uses i_dio_orphaned_slot to index the
slot-local system inode cache. The dinode validator does not check
this active slot, so an out-of-range value produces an invalid cache
entry pointer that is dereferenced as an inode pointer.

[FIX]
Reject an active i_dio_orphaned_slot outside the slot range during
dinode validation, before DIO orphan recovery can consume it.

Fixes: 06ee5c75b575 ("ocfs2: add functions to add and remove inode in orphan dir")
Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
---
 fs/ocfs2/inode.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 358ab3535366..180107a11046 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1536,6 +1536,14 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	if ((le32_to_cpu(di->i_flags) & OCFS2_DIO_ORPHANED_FL) &&
+	    le16_to_cpu(di->i_dio_orphaned_slot) >= OCFS2_SB(sb)->max_slots) {
+		rc = ocfs2_error(sb, "Invalid dinode %llu: DIO orphaned slot %u\n",
+				 (unsigned long long)bh->b_blocknr,
+				 le16_to_cpu(di->i_dio_orphaned_slot));
+		goto bail;
+	}
+
 	/*
 	 * Reject dinodes whose i_mode does not name one of the seven
 	 * canonical POSIX file types.  ocfs2_populate_inode() copies
-- 
2.43.0