From: Al Viro <viro@zeniv.linux.org.uk>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: syzbot <syzbot+96cee7d33ca3f87eee86@syzkaller.appspotmail.com>,
ntfs3@lists.linux.dev, syzkaller-bugs@googlegroups.com,
Mark Fasheh <mark@fasheh.com>,
Christian Brauner <brauner@kernel.org>,
Konstantin Komarov <almaz.alexandrovich@paragon-software.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Hillf Danton <hdanton@sina.com>, linux-mm <linux-mm@kvack.org>,
trix@redhat.com, ndesaulniers@google.com, nathan@kernel.org
Subject: Re: [PATCH] vfs: allow using kernel buffer during fiemap operation
Date: Thu, 20 Apr 2023 22:00:45 +0100 [thread overview]
Message-ID: <20230420210045.GP3390869@ZenIV> (raw)
In-Reply-To: <bc30483b-7f9b-df4e-7143-8646aeb4b5a2@I-love.SAKURA.ne.jp>
On Mon, Apr 17, 2023 at 11:03:26PM +0900, Tetsuo Handa wrote:
> syzbot is reporting circular locking dependency between ntfs_file_mmap()
> (which has mm->mmap_lock => ni->ni_lock => ni->file.run_lock dependency)
> and ntfs_fiemap() (which has ni->ni_lock => ni->file.run_lock =>
> mm->mmap_lock dependency), for commit c4b929b85bdb ("vfs: vfs-level fiemap
> interface") implemented fiemap_fill_next_extent() using copy_to_user()
> where direct mm->mmap_lock dependency is inevitable.
>
> Since ntfs3 does not want to release ni->ni_lock and/or ni->file.run_lock
> in order to make sure that "struct ATTRIB" does not change during
> ioctl(FS_IOC_FIEMAP) request, let's make it possible to call
> fiemap_fill_next_extent() with filesystem locks held.
>
> This patch adds fiemap_fill_next_kernel_extent() which spools
> "struct fiemap_extent" to dynamically allocated kernel buffer, and
> fiemap_copy_kernel_extent() which copies spooled "struct fiemap_extent"
> to userspace buffer after filesystem locks are released.
Ugh... I'm pretty certain that this is a wrong approach. What is going
on in ntfs_file_mmap() that requires that kind of locking?
AFAICS, that's the part that looks odd... Details, please.
next prev parent reply other threads:[~2023-04-20 21:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <000000000000e2102c05eeaf9113@google.com>
[not found] ` <00000000000031b80705ef5d33d1@google.com>
2023-04-12 13:11 ` [PATCH] fs/ntfs3: disable page fault during ntfs_fiemap() Tetsuo Handa
2023-04-12 13:13 ` Matthew Wilcox
2023-04-12 13:29 ` Tetsuo Handa
2023-04-12 14:24 ` Matthew Wilcox
2023-04-17 14:03 ` [PATCH] vfs: allow using kernel buffer during fiemap operation Tetsuo Handa
2023-04-20 21:00 ` Al Viro [this message]
2023-04-20 21:11 ` Al Viro
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