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>

1 files changed, 27 insertions, 4 deletions

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 54eee39f2698..ea80036d7897 100644
--- a/fs/udf/inode.c
+++ b/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) &
-                    (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)