[PATCH v4 2/2] ocfs2: validate external xattr entries when reading metadata

[Cen Zhang <zzzccc427@gmail.com>]

ocfs2_validate_xattr_block() checks the xattr block header before the
block reaches higher-level xattr users, but it does not verify that a
non-indexed block's xh_count and entry offsets fit inside the block.
Indexed buckets likewise reach list/get consumers after ECC without an
entry-bounds check.

Move the non-indexed external xattr entry checks into
ocfs2_validate_xattr_block(). Validate indexed bucket entries
immediately after bucket ECC verification in ocfs2_read_xattr_bucket(),
because buckets do not pass through ocfs2_validate_xattr_block().
The bucket entry table is still bounded by the first bucket block; the
name/value offsets are then checked against the bucket block they target.

Reject corrupted external xattr metadata before listxattr() or
getxattr() can walk out-of-range entry arrays or name/value offsets.

Validation reproduced this kernel report:
BUG: KASAN: use-after-free in ocfs2_xattr_list_entries+0xd7/0x190
Read of size 1 at addr ffff88810a654007 by task ocfs2_xattr_lis/630
Call Trace:
  dump_stack_lvl+0x66/0xa0
  print_report+0xce/0x630
  kasan_report+0xe0/0x110
  ocfs2_xattr_list_entries+0xd7/0x190
  ocfs2_listxattr+0x3f6/0x610
  listxattr+0x90/0xe0
  path_listxattrat+0xed/0x220
  do_syscall_64+0x115/0x6a0
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: cf1d6c763fbc ("ocfs2: Add extended attribute support")
Fixes: 0c044f0b24b9 ("ocfs2: Add xattr bucket iteration for large numbers of EAs")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 fs/ocfs2/xattr.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 00900e65634d..8147d5c5f293 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -390,6 +390,13 @@ static int ocfs2_init_xattr_bucket(struct ocfs2_xattr_bucket *bucket,
 	return rc;
 }
 
+static int ocfs2_validate_xattr_entries(struct super_block *sb, u64 blkno,
+					struct ocfs2_xattr_header *xh,
+					size_t storage_size,
+					const char *where);
+static int ocfs2_validate_xattr_bucket(struct ocfs2_xattr_bucket *bucket,
+				       u64 blkno);
+
 /* Read the xattr bucket at xb_blkno */
 static int ocfs2_read_xattr_bucket(struct ocfs2_xattr_bucket *bucket,
 				   u64 xb_blkno)
@@ -408,6 +415,8 @@ static int ocfs2_read_xattr_bucket(struct ocfs2_xattr_bucket *bucket,
 		spin_unlock(&OCFS2_SB(bucket->bu_inode->i_sb)->osb_xattr_lock);
 		if (rc)
 			mlog_errno(rc);
+		else
+			rc = ocfs2_validate_xattr_bucket(bucket, xb_blkno);
 	}
 
 	if (rc)
@@ -509,6 +518,16 @@ static int ocfs2_validate_xattr_block(struct super_block *sb,
 				   le32_to_cpu(xb->xb_fs_generation));
 	}
 
+	if (!(le16_to_cpu(xb->xb_flags) & OCFS2_XATTR_INDEXED)) {
+		size_t storage_size = sb->s_blocksize -
+			offsetof(struct ocfs2_xattr_block, xb_attrs.xb_header);
+
+		return ocfs2_validate_xattr_entries(sb, bh->b_blocknr,
+						    &xb->xb_attrs.xb_header,
+						    storage_size,
+						    "xattr block");
+	}
+
 	return 0;
 }
 
@@ -1042,6 +1061,71 @@ int ocfs2_validate_inode_xattr(struct super_block *sb, u64 blkno,
 	return ocfs2_validate_xattr_ibody_header(sb, blkno, di, NULL);
 }
 
+static int ocfs2_validate_xattr_bucket(struct ocfs2_xattr_bucket *bucket,
+				       u64 blkno)
+{
+	struct super_block *sb = bucket->bu_inode->i_sb;
+	struct ocfs2_xattr_header *xh = bucket_xh(bucket);
+	size_t blocksize = sb->s_blocksize;
+	size_t bucket_size = blocksize * bucket->bu_blocks;
+	u16 xattr_count = le16_to_cpu(xh->xh_count);
+	size_t max_entries;
+	int i;
+
+	if (bucket_size < sizeof(*xh))
+		return ocfs2_error(sb,
+				   "Invalid xattr bucket %llu: storage size %zu is too small\n",
+				   (unsigned long long)blkno, bucket_size);
+
+	max_entries = (blocksize - sizeof(*xh)) /
+		      sizeof(struct ocfs2_xattr_entry);
+	if (xattr_count > max_entries)
+		return ocfs2_error(sb,
+				   "Invalid xattr bucket %llu: entry count %u exceeds maximum %zu\n",
+				   (unsigned long long)blkno, xattr_count,
+				   max_entries);
+
+	for (i = 0; i < xattr_count; i++) {
+		struct ocfs2_xattr_entry *xe = &xh->xh_entries[i];
+		size_t name_offset = le16_to_cpu(xe->xe_name_offset);
+		size_t block_off = name_offset >> sb->s_blocksize_bits;
+		size_t block_offset = name_offset % blocksize;
+		size_t value_offset;
+
+		if (name_offset >= bucket_size || block_off >= bucket->bu_blocks)
+			return ocfs2_error(sb,
+					   "Invalid xattr bucket %llu: entry %d name block is out of bounds\n",
+					   (unsigned long long)blkno, i);
+
+		if (xe->xe_name_len > blocksize - block_offset)
+			return ocfs2_error(sb,
+					   "Invalid xattr bucket %llu: entry %d name crosses block boundary\n",
+					   (unsigned long long)blkno, i);
+
+		value_offset = block_offset + OCFS2_XATTR_SIZE(xe->xe_name_len);
+		if (value_offset > blocksize)
+			return ocfs2_error(sb,
+					   "Invalid xattr bucket %llu: entry %d value starts out of bounds\n",
+					   (unsigned long long)blkno, i);
+
+		if (ocfs2_xattr_is_local(xe)) {
+			if (le64_to_cpu(xe->xe_value_size) >
+			    blocksize - value_offset)
+				return ocfs2_error(sb,
+						   "Invalid xattr bucket %llu: entry %d value is out of bounds\n",
+						   (unsigned long long)blkno,
+						   i);
+		} else if (sizeof(struct ocfs2_xattr_value_root) >
+			   blocksize - value_offset) {
+			return ocfs2_error(sb,
+					   "Invalid xattr bucket %llu: entry %d value root is out of bounds\n",
+					   (unsigned long long)blkno, i);
+		}
+	}
+
+	return 0;
+}
+
 static int ocfs2_xattr_ibody_lookup_header(struct inode *inode,
 					   struct ocfs2_dinode *di,
 					   struct ocfs2_xattr_header **header)
-- 
2.43.0