[PATCH] ocfs2: validate inline xattr header before listxattr walks it

[ZhengYuan Huang <gality369@gmail.com>]

[BUG]
listxattr() can walk off the end of a dinode block when the inode-body
xattr header is corrupted:

BUG: KASAN: use-after-free in ocfs2_xattr_list_entry+0x1bd/0x370 fs/ocfs2/xattr.c:918
Read of size 13 at addr ffff88800ab5c0c0 by task syz.0.1231/3756

Call Trace:
 ...
 ocfs2_xattr_list_entry+0x1bd/0x370 fs/ocfs2/xattr.c:918
 ocfs2_xattr_list_entries+0x1e1/0x320 fs/ocfs2/xattr.c:938
 ocfs2_xattr_ibody_list fs/ocfs2/xattr.c:982 [inline]
 ocfs2_listxattr+0x4fb/0x980 fs/ocfs2/xattr.c:1044
 vfs_listxattr+0xb4/0x120 fs/xattr.c:493
 listxattr+0x76/0x170 fs/xattr.c:924
 filename_listxattr fs/xattr.c:958 [inline]
 path_listxattrat+0x137/0x320 fs/xattr.c:988
 __do_sys_listxattr fs/xattr.c:1001 [inline]
 ...

[CAUSE]
ocfs2_xattr_ibody_list() computes the inline xattr header from
di->i_xattr_inline_size and passes it straight to
ocfs2_xattr_list_entries(). If corruption inflates xh_count, the list
walk steps past the inline xattr area and eventually past the end of the
4K dinode block. The xe_type load in ocfs2_xattr_get_type() then reads
poisoned memory.

[FIX]
Validate di->i_xattr_inline_size before locating the header, then bound
xh_count by the number of ocfs2_xattr_entry records that fit inside the
claimed inline area. Reject corrupted metadata with ocfs2_error() and
-EFSCORRUPTED instead of iterating past the dinode block.

Signed-off-by: ZhengYuan Huang <gality369@gmail.com>
---
 fs/ocfs2/xattr.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@
 static int ocfs2_xattr_ibody_list(struct inode *inode,
 				  struct ocfs2_dinode *di,
 				  char *buffer,
 				  size_t buffer_size)
 {
 	struct ocfs2_xattr_header *header = NULL;
 	struct ocfs2_inode_info *oi = OCFS2_I(inode);
 	int ret = 0;
+	u16 xattr_count;
+	size_t max_entries;
+	u16 inline_size;
 
 	if (!(oi->ip_dyn_features & OCFS2_INLINE_XATTR_FL))
 		return ret;
 
+	inline_size = le16_to_cpu(di->i_xattr_inline_size);
+
+	if (inline_size > inode->i_sb->s_blocksize ||
+	    inline_size < sizeof(struct ocfs2_xattr_header)) {
+		ocfs2_error(inode->i_sb,
+			    "Invalid xattr inline size %u in inode %llu\n",
+			    inline_size,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
+
 	header = (struct ocfs2_xattr_header *)
 		 ((void *)di + inode->i_sb->s_blocksize -
-		 le16_to_cpu(di->i_xattr_inline_size));
+		 inline_size);
+
+	xattr_count = le16_to_cpu(header->xh_count);
+	max_entries = (inline_size - sizeof(struct ocfs2_xattr_header)) /
+		      sizeof(struct ocfs2_xattr_entry);
+	if (xattr_count > max_entries) {
+		ocfs2_error(inode->i_sb,
+			    "Invalid xattr entry count %u (max %zu) in inode %llu\n",
+			    xattr_count, max_entries,
+			    (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		return -EFSCORRUPTED;
+	}
 
 	ret = ocfs2_xattr_list_entries(inode, header, buffer, buffer_size);
 
 	return ret;
 }
-- 
2.43.0