ext4: strong binding of xattr inode references

To verify that a xattr entry is not pointing to the wrong xattr inode,
we currently check that the target inode has EXT4_EA_INODE_FL flag set and
also the entry size matches the target inode size.

For stronger validation, also incorporate crc32c hash of the value into
the e_hash field. This is done regardless of whether the entry lives in
the inode body or external attribute block.
Signed-off-by: NTahsin Erdogan <tahsin@google.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/xattr.c

@@ -77,8 +77,8 @@ static void ext4_xattr_block_cache_insert(struct mb_cache *,
 static struct buffer_head *
 ext4_xattr_block_cache_find(struct inode *, struct ext4_xattr_header *,
 			    struct mb_cache_entry **);
-static void ext4_xattr_hash_entry(struct ext4_xattr_entry *entry,
-				  void *value_base);
+static __le32 ext4_xattr_hash_entry(char *name, size_t name_len, __le32 *value,
+				    size_t value_count);
 static void ext4_xattr_rehash(struct ext4_xattr_header *);
 
 static const struct xattr_handler * const ext4_xattr_handler_map[] = {
@@ -380,7 +380,9 @@ static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,
 }
 
 static int
-ext4_xattr_inode_verify_hash(struct inode *ea_inode, void *buffer, size_t size)
+ext4_xattr_inode_verify_hashes(struct inode *ea_inode,
+			       struct ext4_xattr_entry *entry, void *buffer,
+			       size_t size)
 {
 	u32 hash;
 
@@ -388,23 +390,35 @@ ext4_xattr_inode_verify_hash(struct inode *ea_inode, void *buffer, size_t size)
 	hash = ext4_xattr_inode_hash(EXT4_SB(ea_inode->i_sb), buffer, size);
 	if (hash != ext4_xattr_inode_get_hash(ea_inode))
 		return -EFSCORRUPTED;
+
+	if (entry) {
+		__le32 e_hash, tmp_data;
+
+		/* Verify entry hash. */
+		tmp_data = cpu_to_le32(hash);
+		e_hash = ext4_xattr_hash_entry(entry->e_name, entry->e_name_len,
+					       &tmp_data, 1);
+		if (e_hash != entry->e_hash)
+			return -EFSCORRUPTED;
+	}
 	return 0;
 }
 
 #define EXT4_XATTR_INODE_GET_PARENT(inode) ((__u32)(inode)->i_mtime.tv_sec)
 
 /*
- * Read the value from the EA inode.
+ * Read xattr value from the EA inode.
  */
 static int
-ext4_xattr_inode_get(struct inode *inode, unsigned long ea_ino, void *buffer,
-		     size_t size)
+ext4_xattr_inode_get(struct inode *inode, struct ext4_xattr_entry *entry,
+		     void *buffer, size_t size)
 {
 	struct mb_cache *ea_inode_cache = EA_INODE_CACHE(inode);
 	struct inode *ea_inode;
 	int err;
 
-	err = ext4_xattr_inode_iget(inode, ea_ino, &ea_inode);
+	err = ext4_xattr_inode_iget(inode, le32_to_cpu(entry->e_value_inum),
+				    &ea_inode);
 	if (err) {
 		ea_inode = NULL;
 		goto out;
@@ -422,7 +436,7 @@ ext4_xattr_inode_get(struct inode *inode, unsigned long ea_ino, void *buffer,
 	if (err)
 		goto out;
 
-	err = ext4_xattr_inode_verify_hash(ea_inode, buffer, size);
+	err = ext4_xattr_inode_verify_hashes(ea_inode, entry, buffer, size);
 	/*
 	 * Compatibility check for old Lustre ea_inode implementation. Old
 	 * version does not have hash validation, but it has a backpointer
@@ -489,9 +503,8 @@ ext4_xattr_block_get(struct inode *inode, int name_index, const char *name,
 		if (size > buffer_size)
 			goto cleanup;
 		if (entry->e_value_inum) {
-			error = ext4_xattr_inode_get(inode,
-					     le32_to_cpu(entry->e_value_inum),
-					     buffer, size);
+			error = ext4_xattr_inode_get(inode, entry, buffer,
+						     size);
 			if (error)
 				goto cleanup;
 		} else {
@@ -539,9 +552,8 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name,
 		if (size > buffer_size)
 			goto cleanup;
 		if (entry->e_value_inum) {
-			error = ext4_xattr_inode_get(inode,
-					     le32_to_cpu(entry->e_value_inum),
-					     buffer, size);
+			error = ext4_xattr_inode_get(inode, entry, buffer,
+						     size);
 			if (error)
 				goto cleanup;
 		} else {
@@ -1400,8 +1412,8 @@ ext4_xattr_inode_cache_find(struct inode *inode, const void *value,
 		    (EXT4_I(ea_inode)->i_flags & EXT4_EA_INODE_FL) &&
 		    i_size_read(ea_inode) == value_len &&
 		    !ext4_xattr_inode_read(ea_inode, ea_data, value_len) &&
-		    !ext4_xattr_inode_verify_hash(ea_inode, ea_data,
-						  value_len) &&
+		    !ext4_xattr_inode_verify_hashes(ea_inode, NULL, ea_data,
+						    value_len) &&
 		    !memcmp(value, ea_data, value_len)) {
 			mb_cache_entry_touch(ea_inode_cache, ce);
 			mb_cache_entry_put(ea_inode_cache, ce);
@@ -1665,12 +1677,36 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
 		here->e_value_size = cpu_to_le32(i->value_len);
 	}
 
-	if (is_block) {
-		if (i->value)
-			ext4_xattr_hash_entry(here, s->base);
-		ext4_xattr_rehash((struct ext4_xattr_header *)s->base);
+	if (i->value) {
+		__le32 hash = 0;
+
+		/* Entry hash calculation. */
+		if (in_inode) {
+			__le32 crc32c_hash;
+
+			/*
+			 * Feed crc32c hash instead of the raw value for entry
+			 * hash calculation. This is to avoid walking
+			 * potentially long value buffer again.
+			 */
+			crc32c_hash = cpu_to_le32(
+				       ext4_xattr_inode_get_hash(new_ea_inode));
+			hash = ext4_xattr_hash_entry(here->e_name,
+						     here->e_name_len,
+						     &crc32c_hash, 1);
+		} else if (is_block) {
+			__le32 *value = s->base + min_offs - new_size;
+
+			hash = ext4_xattr_hash_entry(here->e_name,
+						     here->e_name_len, value,
+						     new_size >> 2);
+		}
+		here->e_hash = hash;
 	}
 
+	if (is_block)
+		ext4_xattr_rehash((struct ext4_xattr_header *)s->base);
+
 	ret = 0;
 out:
 	iput(old_ea_inode);
@@ -2452,9 +2488,7 @@ static int ext4_xattr_move_to_block(handle_t *handle, struct inode *inode,
 
 	/* Save the entry name and the entry value */
 	if (entry->e_value_inum) {
-		error = ext4_xattr_inode_get(inode,
-					     le32_to_cpu(entry->e_value_inum),
-					     buffer, value_size);
+		error = ext4_xattr_inode_get(inode, entry, buffer, value_size);
 		if (error)
 			goto out;
 	} else {
@@ -2944,30 +2978,22 @@ ext4_xattr_block_cache_find(struct inode *inode,
  *
  * Compute the hash of an extended attribute.
  */
-static void ext4_xattr_hash_entry(struct ext4_xattr_entry *entry,
-				  void *value_base)
+static __le32 ext4_xattr_hash_entry(char *name, size_t name_len, __le32 *value,
+				    size_t value_count)
 {
 	__u32 hash = 0;
-	char *name = entry->e_name;
-	int n;
 
-	for (n = 0; n < entry->e_name_len; n++) {
+	while (name_len--) {
 		hash = (hash << NAME_HASH_SHIFT) ^
 		       (hash >> (8*sizeof(hash) - NAME_HASH_SHIFT)) ^
 		       *name++;
 	}
-
-	if (!entry->e_value_inum && entry->e_value_size) {
-		__le32 *value = (__le32 *)((char *)value_base +
-			le16_to_cpu(entry->e_value_offs));
-		for (n = (le32_to_cpu(entry->e_value_size) +
-		     EXT4_XATTR_ROUND) >> EXT4_XATTR_PAD_BITS; n; n--) {
-			hash = (hash << VALUE_HASH_SHIFT) ^
-			       (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^
-			       le32_to_cpu(*value++);
-		}
+	while (value_count--) {
+		hash = (hash << VALUE_HASH_SHIFT) ^
+		       (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^
+		       le32_to_cpu(*value++);
 	}
-	entry->e_hash = cpu_to_le32(hash);
+	return cpu_to_le32(hash);
 }
 
 #undef NAME_HASH_SHIFT