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Date: Tue, 11 Dec 2018 18:36:19 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 2/2] proc: Protect readers of /proc/mounts from remount
Message-ID: <20181211183619.GF2217@ZenIV.linux.org.uk>
References: <20181211172423.7709-1-jack@suse.cz>
 <20181211172423.7709-3-jack@suse.cz>
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On Tue, Dec 11, 2018 at 06:24:23PM +0100, Jan Kara wrote:
> Readers of /proc/mounts (and similar files) are currently unprotected
> from concurrently running remount on the filesystem they are reporting.
> This can not only result in bogus reported information but also in
> confusion in filesystems ->show_options callbacks resulting in
> use-after-free issues or similar (for example ext4 handling of quota
> file names is prone to such races).
> 
> Fix the problem by protecting showing of mount information with
> sb->s_umount semaphore.

Umm...  Which tree is it against and what exactly does your hold_sb() do?