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Subject[PATCH 4.19 042/276] acct_on(): dont mess with freeze protection
Date
From: Al Viro <viro@zeniv.linux.org.uk>

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>

---
fs/internal.h | 2 --
include/linux/mount.h | 2 ++
kernel/acct.c | 4 ++--
3 files changed, 4 insertions(+), 4 deletions(-)

--- a/fs/internal.h
+++ b/fs/internal.h
@@ -80,9 +80,7 @@ extern int sb_prepare_remount_readonly(s

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 *);

/*
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -86,6 +86,8 @@ extern bool mnt_may_suid(struct vfsmount

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,
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -227,7 +227,7 @@ static int acct_on(struct filename *path
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 *path
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;
}

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