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edf7ddbf1c
Missing calls to mntget() (or equivalently, too many calls to mntput())
are hard to detect because mntput() delays freeing mounts using
task_work_add(), then again using call_rcu(). As a result, mnt_count
can often be decremented to -1 without getting a KASAN use-after-free
report. Such cases are still bugs though, and they point to real
use-after-frees being possible.
For an example of this, see the bug fixed by commit 1b0b9cc8d3
("vfs: fsmount: add missing mntget()"), discussed at
https://lkml.kernel.org/linux-fsdevel/20190605135401.GB30925@xxxxxxxxxxxxxxxxxxxxxxxxx/T/#u.
This bug *should* have been trivial to find. But actually, it wasn't
found until syzkaller happened to use fchdir() to manipulate the
reference count just right for the bug to be noticeable.
Address this by making mntput_no_expire() issue a WARN if mnt_count has
become negative.
Suggested-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
57 lines
1.9 KiB
C
57 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* linux/fs/pnode.h
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*
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* (C) Copyright IBM Corporation 2005.
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*/
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#ifndef _LINUX_PNODE_H
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#define _LINUX_PNODE_H
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#include <linux/list.h>
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#include "mount.h"
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#define IS_MNT_SHARED(m) ((m)->mnt.mnt_flags & MNT_SHARED)
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#define IS_MNT_SLAVE(m) ((m)->mnt_master)
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#define IS_MNT_NEW(m) (!(m)->mnt_ns)
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#define CLEAR_MNT_SHARED(m) ((m)->mnt.mnt_flags &= ~MNT_SHARED)
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#define IS_MNT_UNBINDABLE(m) ((m)->mnt.mnt_flags & MNT_UNBINDABLE)
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#define IS_MNT_MARKED(m) ((m)->mnt.mnt_flags & MNT_MARKED)
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#define SET_MNT_MARK(m) ((m)->mnt.mnt_flags |= MNT_MARKED)
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#define CLEAR_MNT_MARK(m) ((m)->mnt.mnt_flags &= ~MNT_MARKED)
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#define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
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#define CL_EXPIRE 0x01
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#define CL_SLAVE 0x02
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#define CL_COPY_UNBINDABLE 0x04
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#define CL_MAKE_SHARED 0x08
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#define CL_PRIVATE 0x10
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#define CL_SHARED_TO_SLAVE 0x20
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#define CL_COPY_MNT_NS_FILE 0x40
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#define CL_COPY_ALL (CL_COPY_UNBINDABLE | CL_COPY_MNT_NS_FILE)
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static inline void set_mnt_shared(struct mount *mnt)
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{
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mnt->mnt.mnt_flags &= ~MNT_SHARED_MASK;
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mnt->mnt.mnt_flags |= MNT_SHARED;
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}
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void change_mnt_propagation(struct mount *, int);
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int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
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struct hlist_head *);
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int propagate_umount(struct list_head *);
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int propagate_mount_busy(struct mount *, int);
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void propagate_mount_unlock(struct mount *);
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void mnt_release_group_id(struct mount *);
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int get_dominating_id(struct mount *mnt, const struct path *root);
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int mnt_get_count(struct mount *mnt);
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void mnt_set_mountpoint(struct mount *, struct mountpoint *,
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struct mount *);
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void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp,
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struct mount *mnt);
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struct mount *copy_tree(struct mount *, struct dentry *, int);
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bool is_path_reachable(struct mount *, struct dentry *,
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const struct path *root);
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int count_mounts(struct mnt_namespace *ns, struct mount *mnt);
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#endif /* _LINUX_PNODE_H */
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