udf: Make stat on symlink report symlink length as st_size

UDF encodes symlinks in a more complex fashion and thus i_size of a
symlink does not match the lenght of a string returned by readlink(2).
This confuses some applications (see bug 191241) and may be considered a
violation of POSIX. Fix the problem by reading the link into page cache
in response to stat(2) call and report the length of the decoded path.

Signed-off-by: Jan Kara <jack@suse.cz>

4 files changed, 33 insertions, 2 deletions

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 3a5ac2221a88..5f643c93f564 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1547,7 +1547,7 @@ reread:
                 break;
         case ICBTAG_FILE_TYPE_SYMLINK:
                 inode->i_data.a_ops = &udf_symlink_aops;
-                inode->i_op = &page_symlink_inode_operations;
+                inode->i_op = &udf_symlink_inode_operations;
                 inode_nohighmem(inode);
                 inode->i_mode = S_IFLNK | S_IRWXUGO;
                 break;
diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 2d65e280748b..babf48d0e553 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -931,7 +931,7 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
         }
 
         inode->i_data.a_ops = &udf_symlink_aops;
-        inode->i_op = &page_symlink_inode_operations;
+        inode->i_op = &udf_symlink_inode_operations;
         inode_nohighmem(inode);
 
         if (iinfo->i_alloc_type != ICBTAG_FLAG_AD_IN_ICB) {
diff --git a/fs/udf/symlink.c b/fs/udf/symlink.c
index 8d619773056b..f7dfef53f739 100644
--- a/fs/udf/symlink.c
+++ b/fs/udf/symlink.c
@@ -152,9 +152,39 @@ out_unmap:
         return err;
 }
 
+static int udf_symlink_getattr(struct vfsmount *mnt, struct dentry *dentry,
+                               struct kstat *stat)
+{
+        struct inode *inode = d_backing_inode(dentry);
+        struct page *page;
+
+        generic_fillattr(inode, stat);
+        page = read_mapping_page(inode->i_mapping, 0, NULL);
+        if (IS_ERR(page))
+                return PTR_ERR(page);
+        /*
+         * UDF uses non-trivial encoding of symlinks so i_size does not match
+         * number of characters reported by readlink(2) which apparently some
+         * applications expect. Also POSIX says that "The value returned in the
+         * st_size field shall be the length of the contents of the symbolic
+         * link, and shall not count a trailing null if one is present." So
+         * let's report the length of string returned by readlink(2) for
+         * st_size.
+         */
+        stat->size = strlen(page_address(page));
+        put_page(page);
+
+        return 0;
+}
+
 /*
  * symlinks can't do much...
  */
 const struct address_space_operations udf_symlink_aops = {
         .readpage               = udf_symlink_filler,
 };
+
+const struct inode_operations udf_symlink_inode_operations = {
+        .get_link       = page_get_link,
+        .getattr        = udf_symlink_getattr,
+};
diff --git a/fs/udf/udfdecl.h b/fs/udf/udfdecl.h
index b608624e7089..63b034984378 100644
--- a/fs/udf/udfdecl.h
+++ b/fs/udf/udfdecl.h
@@ -84,6 +84,7 @@ extern const struct inode_operations udf_dir_inode_operations;
 extern const struct file_operations udf_dir_operations;
 extern const struct inode_operations udf_file_inode_operations;
 extern const struct file_operations udf_file_operations;
+extern const struct inode_operations udf_symlink_inode_operations;
 extern const struct address_space_operations udf_aops;
 extern const struct address_space_operations udf_adinicb_aops;
 extern const struct address_space_operations udf_symlink_aops;