linux-kernel - [PATCH] namei: get rid of unused filename

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Message-Id: <20210901150040.3875227-1-dkadashev@gmail.com>
Date:   Wed,  1 Sep 2021 22:00:40 +0700
From:   Dmitry Kadashev <dkadashev@...il.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Stephen Brennan <stephen.s.brennan@...cle.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dmitry Kadashev <dkadashev@...il.com>
Subject: [PATCH] namei: get rid of unused filename_parentat()

After the switch of kern_path_locked() to __filename_parentat() (to
address use after free bug) nothing is using filename_parentat(). Also,
filename_parentat() is inherently buggy: the "last" output arg
always point to freed memory.

Drop filename_parentat() and rename __filename_parentat() to
filename_parentat().

Link: https://lore.kernel.org/linux-fsdevel/YS9D4AlEsaCxLFV0@infradead.org/
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Dmitry Kadashev <dkadashev@...il.com>
---
On top of https://lore.kernel.org/linux-fsdevel/20210901001341.79887-1-stephen.s.brennan@oracle.com/

 fs/namei.c | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a0122f0016a3..f2af301cc79f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2514,9 +2514,10 @@ static int path_parentat(struct nameidata *nd, unsigned flags,
 	return err;
 }
 
-static int __filename_parentat(int dfd, struct filename *name,
-				unsigned int flags, struct path *parent,
-				struct qstr *last, int *type)
+/* Note: this does not consume "name" */
+static int filename_parentat(int dfd, struct filename *name,
+			     unsigned int flags, struct path *parent,
+			     struct qstr *last, int *type)
 {
 	int retval;
 	struct nameidata nd;
@@ -2538,16 +2539,6 @@ static int __filename_parentat(int dfd, struct filename *name,
 	return retval;
 }
 
-static int filename_parentat(int dfd, struct filename *name,
-				unsigned int flags, struct path *parent,
-				struct qstr *last, int *type)
-{
-	int retval = __filename_parentat(dfd, name, flags, parent, last, type);
-
-	putname(name);
-	return retval;
-}
-
 /* does lookup, returns the object with parent locked */
 struct dentry *kern_path_locked(const char *name, struct path *path)
 {
@@ -2557,8 +2548,7 @@ struct dentry *kern_path_locked(const char *name, struct path *path)
 	int type, error;
 
 	filename = getname_kernel(name);
-	error = __filename_parentat(AT_FDCWD, filename, 0, path,
-				    &last, &type);
+	error = filename_parentat(AT_FDCWD, filename, 0, path, &last, &type);
 	if (error) {
 		d = ERR_PTR(error);
 		goto out;
@@ -3641,7 +3631,7 @@ static struct dentry *__filename_create(int dfd, struct filename *name,
 	 */
 	lookup_flags &= LOOKUP_REVAL;
 
-	error = __filename_parentat(dfd, name, lookup_flags, path, &last, &type);
+	error = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
 	if (error)
 		return ERR_PTR(error);
 
@@ -4003,7 +3993,7 @@ int do_rmdir(int dfd, struct filename *name)
 	int type;
 	unsigned int lookup_flags = 0;
 retry:
-	error = __filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
+	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
 		goto exit1;
 
@@ -4142,7 +4132,7 @@ int do_unlinkat(int dfd, struct filename *name)
 	struct inode *delegated_inode = NULL;
 	unsigned int lookup_flags = 0;
 retry:
-	error = __filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
+	error = filename_parentat(dfd, name, lookup_flags, &path, &last, &type);
 	if (error)
 		goto exit1;
 
@@ -4690,13 +4680,13 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 		target_flags = 0;
 
 retry:
-	error = __filename_parentat(olddfd, from, lookup_flags, &old_path,
-					&old_last, &old_type);
+	error = filename_parentat(olddfd, from, lookup_flags, &old_path,
+				  &old_last, &old_type);
 	if (error)
 		goto put_names;
 
-	error = __filename_parentat(newdfd, to, lookup_flags, &new_path, &new_last,
-				&new_type);
+	error = filename_parentat(newdfd, to, lookup_flags, &new_path, &new_last,
+				  &new_type);
 	if (error)
 		goto exit1;
 
-- 
2.33.0