Commit df33726f authored by Al Viro's avatar Al Viro Committed by Jialin Zhang
Browse files

Make sure nd->path.mnt and nd->path.dentry are always valid pointers 

stable inclusion
from stable-v5.10.162
commit 0cf0ce8fb5b10d669072345ea855de112d0e0a43
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6BTWC

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.10.167&id=0cf0ce8fb5b10d669072345ea855de112d0e0a43



--------------------------------

[ Upstream commit 7d01ef75 ]

Initialize them in set_nameidata() and make sure that terminate_walk() clears them
once the pointers become potentially invalid (i.e. we leave RCU mode or drop them
in non-RCU one).  Currently we have "path_init() always initializes them and nobody
accesses them outside of path_init()/terminate_walk() segments", which is asking
for trouble.

With that change we would have nd->path.{mnt,dentry}
	1) always valid - NULL or pointing to currently allocated objects.
	2) non-NULL while we are successfully walking
	3) NULL when we are not walking at all
	4) contributing to refcounts whenever non-NULL outside of RCU mode.

Fixes: 6c6ec2b0 ("fs: add support for LOOKUP_CACHED")
Reported-by: default avatar <syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com>
Tested-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Conflict：
	fs/namei.c

Signed-off-by: default avatarLi Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: default avatarZhang Yi <yi.zhang@huawei.com>
Reviewed-by: default avatarWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: default avatarJialin Zhang <zhangjialin11@huawei.com>
parent 8c4b5fe6

fs/namei.c

+4 −2
Original line number Diff line number Diff line
@@ -533,6 +533,8 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name) 
	p->stack = p->internal;

	p->dfd = dfd;

	p->name = name;

	p->path.mnt = NULL;

	p->path.dentry = NULL;

	p->total_link_count = old ? old->total_link_count : 0;

	p->saved = old;

	p->state = 0;
@@ -607,6 +609,8 @@ static void terminate_walk(struct nameidata *nd) 
		rcu_read_unlock();

	}

	nd->depth = 0;

	nd->path.mnt = NULL;

	nd->path.dentry = NULL;

}



/* path_put is needed afterwards regardless of success or failure */
@@ -2250,8 +2254,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags) 
	}



	nd->root.mnt = NULL;

	nd->path.mnt = NULL;

	nd->path.dentry = NULL;



	/* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */

	if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) {