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From: Eric Biggers <ebiggers@kernel.org>
To: Deepa Dinamani <deepa.kernel@gmail.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Jeff Layton <jlayton@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] fs/namespace.c: fix use-after-free of mount in mnt_warn_timestamp_expiry()
Date: Sun, 13 Oct 2019 20:22:42 -0700	[thread overview]
Message-ID: <20191014032242.GD10007@sol.localdomain> (raw)
In-Reply-To: <CABeXuvomuEY7-8SJuRDh+MS+fSE9evMudFe6KEdP+y-0D89fJw@mail.gmail.com>

On Sun, Oct 13, 2019 at 07:04:10PM -0700, Deepa Dinamani wrote:
> Thanks for the fix.
> 
> Would it be better to move the check and warning to a place where the
> access is still safe?
> 
> -Deepa

True, we could just do

diff --git a/fs/namespace.c b/fs/namespace.c
index fe0e9e1410fe..9f2ceb542f05 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2764,14 +2764,14 @@ static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
 	if (IS_ERR(mnt))
 		return PTR_ERR(mnt);
 
+	mnt_warn_timestamp_expiry(mountpoint, mnt);
+
 	error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
 	if (error < 0) {
 		mntput(mnt);
 		return error;
 	}
 
-	mnt_warn_timestamp_expiry(mountpoint, mnt);
-
 	return error;
 }

But then the warning ("Mounted %s file system ...") is printed even if
do_add_mount() fails so nothing was actually mounted.

Though, it's just a warning message and I think failures here are rare, so maybe
we don't care.  Al, what do you think?

- Eric

      reply	other threads:[~2019-10-14  3:22 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 23:09 KASAN: use-after-free Read in do_mount syzbot
2019-10-09  7:18 ` [PATCH] fs/namespace.c: fix use-after-free of mount in mnt_warn_timestamp_expiry() Eric Biggers
2019-10-14  2:04   ` Deepa Dinamani
2019-10-14  3:22     ` Eric Biggers [this message]

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