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From: Jan Kara <jack@suse.cz>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: syzbot <syzbot+7d2debdcdb3cb93c1e5e@syzkaller.appspotmail.com>,
	a@unstable.cc, adobriyan@gmail.com, akpm@linux-foundation.org,
	alex.dewar@gmx.co.uk, amir73il@gmail.com,
	anton.ivanov@cambridgegreys.com, b.a.t.m.a.n@lists.open-mesh.org,
	davem@davemloft.net, jack@suse.cz, jdike@addtoit.com,
	kuba@kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-um@lists.infradead.org,
	mareklindner@neomailbox.ch, netdev@vger.kernel.org,
	richard@nod.at, sfr@canb.auug.org.au, sven@narfation.org,
	sw@simonwunderlich.de, syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] proc: Use new_inode not new_inode_pseudo
Date: Mon, 15 Jun 2020 09:38:36 +0200	[thread overview]
Message-ID: <20200615073836.GD9449@quack2.suse.cz> (raw)
In-Reply-To: <87mu58p02g.fsf@x220.int.ebiederm.org>

On Fri 12-06-20 14:15:51, Eric W. Biederman wrote:
> 
> Recently syzbot reported that unmounting proc when there is an ongoing
> inotify watch on the root directory of proc could result in a use
> after free when the watch is removed after the unmount of proc
> when the watcher exits.
> 
> Commit 69879c01a0c3 ("proc: Remove the now unnecessary internal mount
> of proc") made it easier to unmount proc and allowed syzbot to see the
> problem, but looking at the code it has been around for a long time.
> 
> Looking at the code the fsnotify watch should have been removed by
> fsnotify_sb_delete in generic_shutdown_super.  Unfortunately the inode
> was allocated with new_inode_pseudo instead of new_inode so the inode
> was not on the sb->s_inodes list.  Which prevented
> fsnotify_unmount_inodes from finding the inode and removing the watch
> as well as made it so the "VFS: Busy inodes after unmount" warning
> could not find the inodes to warn about them.
> 
> Make all of the inodes in proc visible to generic_shutdown_super,
> and fsnotify_sb_delete by using new_inode instead of new_inode_pseudo.
> The only functional difference is that new_inode places the inodes
> on the sb->s_inodes list.
> 
> I wrote a small test program and I can verify that without changes it
> can trigger this issue, and by replacing new_inode_pseudo with
> new_inode the issues goes away.
> 
> Cc: stable@vger.kernel.org
> Link: https://lkml.kernel.org/r/000000000000d788c905a7dfa3f4@google.com
> Reported-by: syzbot+7d2debdcdb3cb93c1e5e@syzkaller.appspotmail.com
> Fixes: 0097875bd415 ("proc: Implement /proc/thread-self to point at the directory of the current thread")
> Fixes: 021ada7dff22 ("procfs: switch /proc/self away from proc_dir_entry")
> Fixes: 51f0885e5415 ("vfs,proc: guarantee unique inodes in /proc")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Thanks for analysing this! I agree with the analysis and the patch looks
good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/proc/inode.c       | 2 +-
>  fs/proc/self.c        | 2 +-
>  fs/proc/thread_self.c | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index f40c2532c057..28d6105e908e 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -617,7 +617,7 @@ const struct inode_operations proc_link_inode_operations = {
>  
>  struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
>  {
> -	struct inode *inode = new_inode_pseudo(sb);
> +	struct inode *inode = new_inode(sb);
>  
>  	if (inode) {
>  		inode->i_ino = de->low_ino;
> diff --git a/fs/proc/self.c b/fs/proc/self.c
> index ca5158fa561c..72cd69bcaf4a 100644
> --- a/fs/proc/self.c
> +++ b/fs/proc/self.c
> @@ -43,7 +43,7 @@ int proc_setup_self(struct super_block *s)
>  	inode_lock(root_inode);
>  	self = d_alloc_name(s->s_root, "self");
>  	if (self) {
> -		struct inode *inode = new_inode_pseudo(s);
> +		struct inode *inode = new_inode(s);
>  		if (inode) {
>  			inode->i_ino = self_inum;
>  			inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
> diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
> index ac284f409568..a553273fbd41 100644
> --- a/fs/proc/thread_self.c
> +++ b/fs/proc/thread_self.c
> @@ -43,7 +43,7 @@ int proc_setup_thread_self(struct super_block *s)
>  	inode_lock(root_inode);
>  	thread_self = d_alloc_name(s->s_root, "thread-self");
>  	if (thread_self) {
> -		struct inode *inode = new_inode_pseudo(s);
> +		struct inode *inode = new_inode(s);
>  		if (inode) {
>  			inode->i_ino = thread_self_inum;
>  			inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);
> -- 
> 2.20.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

      reply	other threads:[~2020-06-15  7:38 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12  9:24 KASAN: use-after-free Write in fsnotify_detach_connector_from_object syzbot
2020-06-12 19:15 ` [PATCH] proc: Use new_inode not new_inode_pseudo Eric W. Biederman
2020-06-15  7:38   ` Jan Kara [this message]

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