Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name

Linus Torvalds
2017-08-17T00:08:10Z

[-- Attachment #1: Type: text/plain, Size: 671 bytes --]

On Wed, Aug 16, 2017 at 4:51 PM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> *Blink* You are right I missed that.
>
> In which case I am concerned about failures that make it to err_release.
> Unless I am missing something (again) failures that jump to err_release
> won't call mntput and will result in a mnt leak.

Yes, I think you're right.

Maybe this attached patch is better anyway. It's smaller, because it
keeps more closely to the old code, and just adds a mntput() in all
the exit cases, and depends on the "path_get()" to have incremented
the mnt refcount one extra time.

Can you find something in this one?

ENTIRELY UNTESTED!

Linus

[-- Attachment #2: patch.diff --]
[-- Type: text/plain, Size: 2883 bytes --]

drivers/tty/pty.c | 7 +++++--
fs/devpts/inode.c | 4 +++-
include/linux/devpts_fs.h | 2 +-
3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 284749fb0f6b..1fc80ea87c13 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -793,6 +793,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
struct tty_struct *tty;
struct path *pts_path;
struct dentry *dentry;
+ struct vfsmount *mnt;
int retval;
int index;

@@ -805,7 +806,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
if (retval)
return retval;

- fsi = devpts_acquire(filp);
+ fsi = devpts_acquire(filp, &mnt);
if (IS_ERR(fsi)) {
retval = PTR_ERR(fsi);
goto out_free_file;
@@ -849,7 +850,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
pts_path = kmalloc(sizeof(struct path), GFP_KERNEL);
if (!pts_path)
goto err_release;
- pts_path->mnt = filp->f_path.mnt;
+ pts_path->mnt = mnt;
pts_path->dentry = dentry;
path_get(pts_path);
tty->link->driver_data = pts_path;
@@ -866,6 +867,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
path_put(pts_path);
kfree(pts_path);
err_release:
+ mntput(mnt);
tty_unlock(tty);
// This will also put-ref the fsi
tty_release(inode, filp);
@@ -874,6 +876,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
devpts_kill_index(fsi, index);
out_put_fsi:
devpts_release(fsi);
+ mntput(mnt);
out_free_file:
tty_free_file(filp);
return retval;
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 108df2e3602c..44dfbca9306f 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -133,7 +133,7 @@ static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
return sb->s_fs_info;
}

-struct pts_fs_info *devpts_acquire(struct file *filp)
+struct pts_fs_info *devpts_acquire(struct file *filp, struct vfsmount **ptsmnt)
{
struct pts_fs_info *result;
struct path path;
@@ -142,6 +142,7 @@ struct pts_fs_info *devpts_acquire(struct file *filp)

path = filp->f_path;
path_get(&path);
+ *ptsmnt = NULL;

/* Has the devpts filesystem already been found? */
sb = path.mnt->mnt_sb;
@@ -165,6 +166,7 @@ struct pts_fs_info *devpts_acquire(struct file *filp)
* pty code needs to hold extra references in case of last /dev/tty close
*/
atomic_inc(&sb->s_active);
+ *ptsmnt = mntget(path.mnt);
result = DEVPTS_SB(sb);

out:
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 277ab9af9ac2..7883e901f65c 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -19,7 +19,7 @@

struct pts_fs_info;

-struct pts_fs_info *devpts_acquire(struct file *);
+struct pts_fs_info *devpts_acquire(struct file *, struct vfsmount **ptsmnt);
void devpts_release(struct pts_fs_info *);

int devpts_new_index(struct pts_fs_info *);