[PATCH] udf: augment owner permissions on new inodes

[Steven J. Magnani]

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 granting UDF delete and change attribute permissions
to the owner when creating a new inode.

Reported by: Ty Young
Signed-off-by: Steven J. Magnani <steve@xxxxxxxxxxxxxxx>
---
--- a/fs/udf/udf_i.h	2019-08-14 07:24:05.029508342 -0500
+++ b/fs/udf/udf_i.h	2019-08-19 08:55:37.797394177 -0500
@@ -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 */
--- a/fs/udf/ialloc.c	2019-08-14 07:24:05.029508342 -0500
+++ b/fs/udf/ialloc.c	2019-08-19 08:33:08.992422457 -0500
@@ -118,6 +118,7 @@ struct inode *udf_new_inode(struct inode
 	iinfo->i_lenAlloc = 0;
 	iinfo->i_use = 0;
 	iinfo->i_checkpoint = 1;
+	iinfo->i_extraPerms = FE_PERM_U_DELETE | FE_PERM_U_CHATTR;
 	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))
--- a/fs/udf/inode.c	2019-08-14 07:24:05.029508342 -0500
+++ b/fs/udf/inode.c	2019-08-19 08:42:46.537530051 -0500
@@ -45,6 +45,10 @@
 
 #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)
+
 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 +1462,8 @@ 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);
@@ -1691,10 +1697,7 @@ static int udf_update_inode(struct inode
 		   ((inode->i_mode & 0070) << 2) |
 		   ((inode->i_mode & 0700) << 4);
 
-	udfperms |= (le32_to_cpu(fe->permissions) &
-		    (FE_PERM_O_DELETE | FE_PERM_O_CHATTR |
-		     FE_PERM_G_DELETE | FE_PERM_G_CHATTR |
-		     FE_PERM_U_DELETE | FE_PERM_U_CHATTR));
+	udfperms |= iinfo->i_extraPerms;
 	fe->permissions = cpu_to_le32(udfperms);
 
 	if (S_ISDIR(inode->i_mode) && inode->i_nlink > 0)