udf: Clean up handling of invalid uid/gid

Current code relies on the fact that invalid uid/gid as defined by UDF
2.60 3.3.3.1 and 3.3.3.2 coincides with invalid uid/gid as used by the
user namespaces implementation. Since this is only lucky coincidence,
clean this up to avoid future surprises in case user namespaces
implementation changes. Also this is more robust in presence of valid
(from UDF point of view) uids / gids which do not map into current user
namespace.
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/inode.c

@@ -1275,6 +1275,7 @@ static int udf_read_inode(struct inode *inode, bool hidden_inode)
 	unsigned int indirections = 0;
 	int bs = inode->i_sb->s_blocksize;
 	int ret = -EIO;
+	uint32_t uid, gid;
 
 reread:
 	if (iloc->partitionReferenceNum >= sbi->s_partitions) {
@@ -1400,15 +1401,19 @@ static int udf_read_inode(struct inode *inode, bool hidden_inode)
 
 	ret = -EIO;
 	read_lock(&sbi->s_cred_lock);
-	i_uid_write(inode, le32_to_cpu(fe->uid));
-	if (!uid_valid(inode->i_uid) ||
+	uid = le32_to_cpu(fe->uid);
+	if (uid == UDF_INVALID_ID ||
 	    UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_UID_SET))
-		inode->i_uid = UDF_SB(inode->i_sb)->s_uid;
+		inode->i_uid = sbi->s_uid;
+	else
+		i_uid_write(inode, uid);
 
-	i_gid_write(inode, le32_to_cpu(fe->gid));
-	if (!gid_valid(inode->i_gid) ||
+	gid = le32_to_cpu(fe->gid);
+	if (gid == UDF_INVALID_ID ||
 	    UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_GID_SET))
-		inode->i_gid = UDF_SB(inode->i_sb)->s_gid;
+		inode->i_gid = sbi->s_gid;
+	else
+		i_gid_write(inode, gid);
 
 	if (fe->icbTag.fileType != ICBTAG_FILE_TYPE_DIRECTORY &&
 			sbi->s_fmode != UDF_INVALID_MODE)
@@ -1653,12 +1658,12 @@ static int udf_update_inode(struct inode *inode, int do_sync)
 	}
 
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_UID_FORGET))
-		fe->uid = cpu_to_le32(-1);
+		fe->uid = cpu_to_le32(UDF_INVALID_ID);
 	else
 		fe->uid = cpu_to_le32(i_uid_read(inode));
 
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_GID_FORGET))
-		fe->gid = cpu_to_le32(-1);
+		fe->gid = cpu_to_le32(UDF_INVALID_ID);
 	else
 		fe->gid = cpu_to_le32(i_gid_read(inode));
 

fs/udf/udfdecl.h

@@ -48,6 +48,8 @@ extern __printf(3, 4) void _udf_warn(struct super_block *sb,
 #define UDF_EXTENT_LENGTH_MASK	0x3FFFFFFF
 #define UDF_EXTENT_FLAG_MASK	0xC0000000
 
+#define UDF_INVALID_ID ((uint32_t)-1)
+
 #define UDF_NAME_PAD		4
 #define UDF_NAME_LEN		254
 #define UDF_NAME_LEN_CS0	255