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>

5 files changed, 35 insertions, 4 deletions

diff --git a/fs/udf/file.c b/fs/udf/file.c
index cd31e4f6d6da..628941a6b79a 100644
--- a/fs/udf/file.c
+++ b/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;
diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
index f8e5872f7cc2..0adb40718a5d 100644
--- a/fs/udf/ialloc.c
+++ b/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))
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)
diff --git a/fs/udf/udf_i.h b/fs/udf/udf_i.h
index 00d773d1b7cf..4245d1f63258 100644
--- a/fs/udf/udf_i.h
+++ b/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 */
diff --git a/fs/udf/udfdecl.h b/fs/udf/udfdecl.h
index 65e243ebeb9c..9dd0814f1077 100644
--- a/fs/udf/udfdecl.h
+++ b/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,