acct_on(): don't mess with freeze protection

BugLink: https://bugs.launchpad.net/bugs/1837517
commit 9419a3191dcb27f24478d288abaab697228d28e6 upstream.

What happens there is that we are replacing file->path.mnt of
a file we'd just opened with a clone and we need the write
count contribution to be transferred from original mount to
new one.  That's it.  We do *NOT* want any kind of freeze
protection for the duration of switchover.

IOW, we should just use __mnt_{want,drop}_write() for that
switchover; no need to bother with mnt_{want,drop}_write()
there.

Tested-by: Amir Goldstein <amir73il@gmail.com>
Reported-by: syzbot+2a73a6ea9507b7112141@syzkaller.appspotmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/fs/internal.h b/fs/internal.h
index d410186bc369f9625d492387e3a99e6bcbb99703..d109665b9e50f4e525d0d82a3074127ffe1a556c 100644 (file)
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -80,9 +80,7 @@ extern int sb_prepare_remount_readonly(struct super_block *);
 
 extern void __init mnt_init(void);
 
-extern int __mnt_want_write(struct vfsmount *);
 extern int __mnt_want_write_file(struct file *);
-extern void __mnt_drop_write(struct vfsmount *);
 extern void __mnt_drop_write_file(struct file *);
 
 /*

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 037eed52164bd161b671c1097958b74a663f0f6a..03138a0f46f9d4f39cf2be877773b59001479b70 100644 (file)
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -86,6 +86,8 @@ extern bool mnt_may_suid(struct vfsmount *mnt);
 
 struct path;
 extern struct vfsmount *clone_private_mount(const struct path *path);
+extern int __mnt_want_write(struct vfsmount *);
+extern void __mnt_drop_write(struct vfsmount *);
 
 struct file_system_type;
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,

diff --git a/kernel/acct.c b/kernel/acct.c
index addf7732fb562f5b0eb51a0bd8894aec81cc8afe..81f9831a785925382824fd765f574941d08e9e01 100644 (file)
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -227,7 +227,7 @@ static int acct_on(struct filename *pathname)
                filp_close(file, NULL);
                return PTR_ERR(internal);
        }
-       err = mnt_want_write(internal);
+       err = __mnt_want_write(internal);
        if (err) {
                mntput(internal);
                kfree(acct);
@@ -252,7 +252,7 @@ static int acct_on(struct filename *pathname)
        old = xchg(&ns->bacct, &acct->pin);
        mutex_unlock(&acct->lock);
        pin_kill(old);
-       mnt_drop_write(mnt);
+       __mnt_drop_write(mnt);
        mntput(mnt);
        return 0;
 }