[PATCH v2 3/4] isofs: pass the name buffer size to get_rock_ridge_filename()

[Matthias Goergens <matthias.goergens@gmail.com>]

get_rock_ridge_filename() assembles a name from one or more NM entries
into a buffer allocated by its caller.  It is not told how big that
buffer is, and instead stops adding NM entries once the name would
exceed NAME_MAX, relying on the callers' buffer being larger.

Pass the size in and check against it.  Both callers pass NAME_MAX + 1,
so the behaviour is unchanged: an NM entry that would take the name
past 255 bytes is dropped, together with any that follow, and the
entries before it are returned.

Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
---
 fs/isofs/dir.c   | 3 ++-
 fs/isofs/isofs.h | 3 ++-
 fs/isofs/namei.c | 3 ++-
 fs/isofs/rock.c  | 8 ++++++--
 4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/isofs/dir.c b/fs/isofs/dir.c
index eebea133094d..dd8958617340 100644
--- a/fs/isofs/dir.c
+++ b/fs/isofs/dir.c
@@ -186,7 +186,8 @@ static int do_isofs_readdir(struct inode *inode, struct file *file,
 
 		map = 1;
 		if (sbi->s_rock) {
-			len = get_rock_ridge_filename(de, tmpname, inode);
+			len = get_rock_ridge_filename(de, tmpname, NAME_MAX + 1,
+						      inode);
 			if (len != 0) {		/* may be -1 */
 				p = tmpname;
 				map = 0;
diff --git a/fs/isofs/isofs.h b/fs/isofs/isofs.h
index 47c43a3c6a61..a2d28a23e892 100644
--- a/fs/isofs/isofs.h
+++ b/fs/isofs/isofs.h
@@ -115,7 +115,8 @@ struct timespec64 iso_date(u8 *p, int flags);
 struct inode;		/* To make gcc happy */
 
 extern int parse_rock_ridge_inode(struct iso_directory_record *, struct inode *, int relocated);
-extern int get_rock_ridge_filename(struct iso_directory_record *, char *, struct inode *);
+int get_rock_ridge_filename(struct iso_directory_record *de, char *retname,
+			    int retnamesize, struct inode *inode);
 extern int isofs_name_translate(struct iso_directory_record *, char *, struct inode *);
 bool isofs_dir_record_valid(struct iso_directory_record *de,
 			    unsigned long offset,
diff --git a/fs/isofs/namei.c b/fs/isofs/namei.c
index c65cc78583ba..9025ff74eb60 100644
--- a/fs/isofs/namei.c
+++ b/fs/isofs/namei.c
@@ -104,7 +104,8 @@ isofs_find_entry(struct inode *dir, struct dentry *dentry,
 		dpnt = de->name;
 
 		if (sbi->s_rock &&
-		    ((i = get_rock_ridge_filename(de, tmpname, dir)))) {
+		    ((i = get_rock_ridge_filename(de, tmpname, NAME_MAX + 1,
+						  dir)))) {
 			dlen = i;	/* possibly -1 */
 			dpnt = tmpname;
 #ifdef CONFIG_JOLIET
diff --git a/fs/isofs/rock.c b/fs/isofs/rock.c
index 84e0d764c210..5a5984b72224 100644
--- a/fs/isofs/rock.c
+++ b/fs/isofs/rock.c
@@ -209,10 +209,14 @@ static int rock_check_overflow(struct rock_state *rs, int sig)
 }
 
 /*
+ * Build the Rock Ridge name of @de in @retname, a buffer of @retnamesize
+ * bytes.  From the first NM entry that does not fit along with the
+ * terminator, the rest of the name is dropped.
+ *
  * return length of name field; 0: not found, -1: to be ignored
  */
 int get_rock_ridge_filename(struct iso_directory_record *de,
-			    char *retname, struct inode *inode)
+			    char *retname, int retnamesize, struct inode *inode)
 {
 	struct rock_state rs;
 	struct rock_ridge *rr;
@@ -287,7 +291,7 @@ int get_rock_ridge_filename(struct iso_directory_record *de,
 				break;
 			}
 			len = rr->len - 5;
-			if (retnamlen + len > NAME_MAX) {
+			if (retnamlen + len >= retnamesize) {
 				truncate = 1;
 				break;
 			}
-- 
2.55.0