udf: augment UDF permissions on new inodes

Windows presents files created within Linux as read-only, even when
permissions in Linux indicate the file should be writable.

UDF defines a slightly different set of basic file permissions than Linux.
Specifically, UDF has "delete" and "change attribute" permissions for each
access class (user/group/other). Linux has no equivalents for these.

When the Linux UDF driver creates a file (or directory), no UDF delete or
change attribute permissions are granted. The lack of delete permission
appears to cause Windows to mark an item read-only when its permissions
otherwise indicate that it should be read-write.

Fix this by having UDF delete permissions track Linux write permissions.
Also grant UDF change attribute permission to the owner when creating a
new inode.

Reported by: Ty Young
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Link: https://lore.kernel.org/r/20190827121359.9954-1-steve@digidescorp.com
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/file.c

@@ -280,6 +280,9 @@ static int udf_setattr(struct dentry *dentry, struct iattr *attr)
 			return error;
 	}
 
+	if (attr->ia_valid & ATTR_MODE)
+		udf_update_extra_perms(inode, attr->ia_mode);
+
 	setattr_copy(inode, attr);
 	mark_inode_dirty(inode);
 	return 0;

fs/udf/ialloc.c

@@ -118,6 +118,9 @@ struct inode *udf_new_inode(struct inode *dir, umode_t mode)
 	iinfo->i_lenAlloc = 0;
 	iinfo->i_use = 0;
 	iinfo->i_checkpoint = 1;
+	iinfo->i_extraPerms = FE_PERM_U_CHATTR;
+	udf_update_extra_perms(inode, mode);
+
 	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
 		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
 	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))

fs/udf/inode.c

@@ -45,6 +45,13 @@
 
 #define EXTENT_MERGE_SIZE 5
 
+#define FE_MAPPED_PERMS	(FE_PERM_U_READ | FE_PERM_U_WRITE | FE_PERM_U_EXEC | \
+			 FE_PERM_G_READ | FE_PERM_G_WRITE | FE_PERM_G_EXEC | \
+			 FE_PERM_O_READ | FE_PERM_O_WRITE | FE_PERM_O_EXEC)
+
+#define FE_DELETE_PERMS	(FE_PERM_U_DELETE | FE_PERM_G_DELETE | \
+			 FE_PERM_O_DELETE)
+
 static umode_t udf_convert_permissions(struct fileEntry *);
 static int udf_update_inode(struct inode *, int);
 static int udf_sync_inode(struct inode *inode);
@@ -1458,6 +1465,8 @@ reread:
 	else
 		inode->i_mode = udf_convert_permissions(fe);
 	inode->i_mode &= ~sbi->s_umask;
+	iinfo->i_extraPerms = le32_to_cpu(fe->permissions) & ~FE_MAPPED_PERMS;
+
 	read_unlock(&sbi->s_cred_lock);
 
 	link_count = le16_to_cpu(fe->fileLinkCount);
@@ -1631,6 +1640,23 @@ static umode_t udf_convert_permissions(struct fileEntry *fe)
 	return mode;
 }
 
+void udf_update_extra_perms(struct inode *inode, umode_t mode)
+{
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	/*
+	 * UDF 2.01 sec. 3.3.3.3 Note 2:
+	 * In Unix, delete permission tracks write
+	 */
+	iinfo->i_extraPerms &= ~FE_DELETE_PERMS;
+	if (mode & 0200)
+		iinfo->i_extraPerms |= FE_PERM_U_DELETE;
+	if (mode & 0020)
+		iinfo->i_extraPerms |= FE_PERM_G_DELETE;
+	if (mode & 0002)
+		iinfo->i_extraPerms |= FE_PERM_O_DELETE;
+}
+
 int udf_write_inode(struct inode *inode, struct writeback_control *wbc)
 {
 	return udf_update_inode(inode, wbc->sync_mode == WB_SYNC_ALL);
@@ -1703,10 +1729,7 @@ static int udf_update_inode(struct inode *inode, int do_sync)
 		   ((inode->i_mode & 0070) << 2) |
 		   ((inode->i_mode & 0700) << 4);
 
-	udfperms |= (le32_to_cpu(fe->permissions) &
+	udfperms |= iinfo->i_extraPerms;
-		    (FE_PERM_O_DELETE | FE_PERM_O_CHATTR |
-		     FE_PERM_G_DELETE | FE_PERM_G_CHATTR |
-		     FE_PERM_U_DELETE | FE_PERM_U_CHATTR));
 	fe->permissions = cpu_to_le32(udfperms);
 
 	if (S_ISDIR(inode->i_mode) && inode->i_nlink > 0)

fs/udf/udf_i.h

@@ -38,6 +38,7 @@ struct udf_inode_info {
 	__u32			i_next_alloc_block;
 	__u32			i_next_alloc_goal;
 	__u32			i_checkpoint;
+	__u32			i_extraPerms;
 	unsigned		i_alloc_type : 3;
 	unsigned		i_efe : 1;	/* extendedFileEntry */
 	unsigned		i_use : 1;	/* unallocSpaceEntry */

fs/udf/udfdecl.h

@@ -170,6 +170,7 @@ extern int8_t udf_next_aext(struct inode *, struct extent_position *,
 			    struct kernel_lb_addr *, uint32_t *, int);
 extern int8_t udf_current_aext(struct inode *, struct extent_position *,
 			       struct kernel_lb_addr *, uint32_t *, int);
+extern void udf_update_extra_perms(struct inode *inode, umode_t mode);
 
 /* misc.c */
 extern struct buffer_head *udf_tgetblk(struct super_block *sb,