From: Catalin Marinas <catalin.marinas@arm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
cluster-devel <cluster-devel@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>,
Josef Bacik <josef@toxicpanda.com>, Will Deacon <will@kernel.org>
Subject: Re: [RFC][arm64] possible infinite loop in btrfs search_ioctl()
Date: Fri, 22 Oct 2021 10:34:00 +0100 [thread overview]
Message-ID: <YXKFiBzaBcz9EiOI@arm.com> (raw)
In-Reply-To: <CAHk-=wgvnU2PXFMpsNErdwE=tXGymLHe275jWkBhCbGiixWU5g@mail.gmail.com>
On Thu, Oct 21, 2021 at 04:30:30PM -1000, Linus Torvalds wrote:
> On Thu, Oct 21, 2021 at 4:42 AM Andreas Gruenbacher <agruenba@redhat.com> wrote:
> > But probing the entire memory range in fault domain granularity in the
> > page fault-in functions still doesn't actually make sense. Those
> > functions really only need to guarantee that we'll be able to make
> > progress eventually. From that point of view, it should be enough to
> > probe the first byte of the requested memory range
>
> That's probably fine.
>
> Although it should be more than one byte - "copy_from_user()" might do
> word-at-a-time optimizations, so you could have an infinite loop of
>
> (a) copy_from_user() fails because the chunk it tried to get failed partly
>
> (b) fault_in() probing succeeds, because the beginning part is fine
>
> so I agree that the fault-in code doesn't need to do the whole area,
> but it needs to at least do some <N bytes, up to length> thing, to
> handle the situation where the copy_to/from_user requires more than a
> single byte.
From a discussion with Al some months ago, if there are bytes still
accessible, copy_from_user() is not allowed to fail fully (i.e. return
the requested copy size) even when it uses word-at-a-time. In the worst
case, it should return size - 1. If the fault_in() then continues
probing from uaddr + 1, it should eventually hit the faulty address.
The problem appears when fault_in() restarts from uaddr rather than
where copy_from_user() stopped. That's what the btrfs search_ioctl()
does. I also need to check the direct I/O cases that Andreas mentioned,
maybe they can be changed not to attempt the fault_in() from the
beginning of the block.
--
Catalin
next prev parent reply other threads:[~2021-10-22 9:34 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 16:49 [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 01/19] iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value Andreas Gruenbacher
2021-09-09 11:09 ` Christoph Hellwig
2021-08-27 16:49 ` [PATCH v7 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 03/19] gup: Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-08-27 19:08 ` Al Viro
2021-09-03 14:56 ` Filipe Manana
2021-09-28 15:02 ` Andreas Gruenbacher
2021-09-28 16:37 ` Matthew Wilcox
2021-09-28 20:41 ` Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 04/19] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-27 18:53 ` Al Viro
2021-08-27 18:57 ` Linus Torvalds
2021-08-27 19:16 ` Al Viro
2021-08-27 20:56 ` Kari Argillander
2021-08-28 17:13 ` Linus Torvalds
2021-08-27 16:49 ` [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-27 18:49 ` Al Viro
2021-08-27 19:05 ` Linus Torvalds
2021-08-27 19:23 ` Al Viro
2021-08-27 19:33 ` Linus Torvalds
2021-08-27 19:37 ` Al Viro
2021-08-27 21:48 ` Al Viro
2021-08-27 21:57 ` Al Viro
2021-08-27 23:22 ` Luck, Tony
2021-08-28 2:20 ` Luck, Tony
2021-08-28 21:47 ` Thomas Gleixner
2021-08-28 22:04 ` Al Viro
2021-08-28 22:11 ` Al Viro
2021-08-28 22:19 ` Al Viro
2021-08-28 22:51 ` Al Viro
2021-08-29 18:44 ` Thomas Gleixner
2021-08-29 19:46 ` Al Viro
2021-08-29 19:51 ` Thomas Gleixner
2021-08-28 22:20 ` Tony Luck
2021-08-29 1:40 ` Matthew Wilcox
2021-08-30 15:41 ` Luck, Tony
2021-08-28 22:23 ` Thomas Gleixner
2021-08-28 19:28 ` [RFC][arm64] possible infinite loop in btrfs search_ioctl() Al Viro
2021-08-31 13:54 ` Catalin Marinas
2021-08-31 15:28 ` Al Viro
2021-08-31 16:01 ` Catalin Marinas
2021-10-11 17:37 ` Catalin Marinas
2021-10-11 19:15 ` Linus Torvalds
2021-10-11 21:08 ` Catalin Marinas
2021-10-11 23:59 ` Linus Torvalds
2021-10-12 17:27 ` Catalin Marinas
2021-10-12 17:58 ` Linus Torvalds
2021-10-18 17:13 ` Catalin Marinas
2021-10-21 0:46 ` Andreas Gruenbacher
2021-10-21 10:05 ` Catalin Marinas
2021-10-21 14:42 ` Andreas Gruenbacher
2021-10-21 17:09 ` Catalin Marinas
2021-10-21 18:00 ` Andreas Gruenbacher
2021-10-22 18:41 ` Catalin Marinas
2021-10-25 19:37 ` Andreas Gruenbacher
2021-10-22 2:30 ` Linus Torvalds
2021-10-22 9:34 ` Catalin Marinas [this message]
2021-08-29 0:58 ` [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Al Viro
2021-08-27 16:49 ` [PATCH v7 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 12/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 13/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 14/19] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-09-03 18:54 ` Darrick J. Wong
2021-09-09 11:17 ` Christoph Hellwig
2021-08-27 16:49 ` [PATCH v7 15/19] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-09-03 18:54 ` Darrick J. Wong
2021-09-09 11:20 ` Christoph Hellwig
2021-09-28 15:05 ` Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 16/19] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-27 18:30 ` Darrick J. Wong
2021-08-27 20:15 ` Andreas Gruenbacher
2021-08-27 21:32 ` Darrick J. Wong
2021-08-27 21:49 ` Andreas Grünbacher
2021-08-27 22:35 ` Linus Torvalds
2021-09-03 18:47 ` Darrick J. Wong
2021-09-03 18:53 ` Darrick J. Wong
2021-09-09 11:30 ` Christoph Hellwig
2021-09-09 17:22 ` Linus Torvalds
2021-09-10 7:36 ` Christoph Hellwig
2021-08-27 16:49 ` [PATCH v7 17/19] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-09-09 11:36 ` Christoph Hellwig
2021-09-09 17:17 ` Linus Torvalds
2021-09-10 7:24 ` Christoph Hellwig
2021-08-27 16:49 ` [PATCH v7 18/19] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-08-27 18:47 ` Al Viro
2021-08-27 19:56 ` Andreas Gruenbacher
2021-08-27 16:49 ` [PATCH v7 19/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-27 17:16 ` [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-09-01 19:52 ` Andreas Gruenbacher
2021-09-03 15:52 ` Linus Torvalds
2021-09-03 18:25 ` Al Viro
2021-09-03 18:47 ` Linus Torvalds
2021-09-03 15:07 ` Filipe Manana
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