From: Catalin Marinas <catalin.marinas@arm.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: cluster-devel <cluster-devel@redhat.com>, Jan Kara <jack@suse.cz>,
Andreas Gruenbacher <agruenba@redhat.com>,
Will Deacon <will@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Josef Bacik <josef@toxicpanda.com>,
Christoph Hellwig <hch@infradead.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
"ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>
Subject: Re: [Ocfs2-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl()
Date: Tue, 31 Aug 2021 14:54:50 +0100 [thread overview]
Message-ID: <YS40qqmXL7CMFLGq@arm.com> (raw)
In-Reply-To: <YSqOUb7yZ7kBoKRY@zeniv-ca.linux.org.uk>
On Sat, Aug 28, 2021 at 08:28:17PM +0100, Al Viro wrote:
> AFAICS, a48b73eca4ce "btrfs: fix potential deadlock in the search ioctl"
> has introduced a bug at least on arm64.
>
> Relevant bits: in search_ioctl() we have
> while (1) {
> ret = fault_in_pages_writeable(ubuf + sk_offset,
> *buf_size - sk_offset);
> if (ret)
> break;
>
> ret = btrfs_search_forward(root, &key, path, sk->min_transid);
> if (ret != 0) {
> if (ret > 0)
> ret = 0;
> goto err;
> }
> ret = copy_to_sk(path, &key, sk, buf_size, ubuf,
> &sk_offset, &num_found);
> btrfs_release_path(path);
> if (ret)
> break;
>
> }
> and in copy_to_sk() -
> sh.objectid = key->objectid;
> sh.offset = key->offset;
> sh.type = key->type;
> sh.len = item_len;
> sh.transid = found_transid;
>
> /*
> * Copy search result header. If we fault then loop again so we
> * can fault in the pages and -EFAULT there if there's a
> * problem. Otherwise we'll fault and then copy the buffer in
> * properly this next time through
> */
> if (copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh))) {
> ret = 0;
> goto out;
> }
> with sk_offset left unchanged if the very first copy_to_user_nofault() fails.
>
> Now, consider a situation on arm64 where ubuf points to the beginning of page,
> ubuf[0] can be accessed, but ubuf[16] can not (possible with MTE, AFAICS). We do
> fault_in_pages_writeable(), which succeeds. When we get to copy_to_user_nofault()
> we fail as soon as it gets past the first 16 bytes. And we repeat everything from
> scratch, with no progress made, since short copies are treated as "discard and
> repeat" here.
So if copy_to_user_nofault() returns -EFAULT, copy_to_sk() returns 0
(following commit a48b73eca4ce). I think you are right, search_ioctl()
can get into an infinite loop attempting to write to user if the
architecture can trigger faults at smaller granularity than the page
boundary. fault_in_pages_writeable() won't fix it if ubuf[0] is
writable and doesn't trigger an MTE tag check fault.
An arm64-specific workaround would be for pagefault_disable() to disable
tag checking. It's a pretty big hammer, weakening the out of bounds
access detection of MTE. My preference would be a fix in the btrfs code.
A btrfs option would be for copy_to_sk() to return an indication of
where the fault occurred and get fault_in_pages_writeable() to check
that location, even if the copying would restart from an earlier offset
(this requires open-coding copy_to_user_nofault()). An attempt below,
untested and does not cover read_extent_buffer_to_user_nofault():
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0ba98e08a029..9e74ba1c955d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2079,6 +2079,7 @@ static noinline int copy_to_sk(struct btrfs_path *path,
size_t *buf_size,
char __user *ubuf,
unsigned long *sk_offset,
+ unsigned long *fault_offset,
int *num_found)
{
u64 found_transid;
@@ -2143,7 +2144,11 @@ static noinline int copy_to_sk(struct btrfs_path *path,
* problem. Otherwise we'll fault and then copy the buffer in
* properly this next time through
*/
- if (copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh))) {
+ pagefault_disable();
+ ret = __copy_to_user_inatomic(ubuf + *sk_offset, &sh, sizeof(sh));
+ pagefault_enable();
+ *fault_offset = *sk_offset + sizeof(sh) - ret;
+ if (ret) {
ret = 0;
goto out;
}
@@ -2218,6 +2223,7 @@ static noinline int search_ioctl(struct inode *inode,
int ret;
int num_found = 0;
unsigned long sk_offset = 0;
+ unsigned long fault_offset = 0;
if (*buf_size < sizeof(struct btrfs_ioctl_search_header)) {
*buf_size = sizeof(struct btrfs_ioctl_search_header);
@@ -2244,8 +2250,8 @@ static noinline int search_ioctl(struct inode *inode,
key.offset = sk->min_offset;
while (1) {
- ret = fault_in_pages_writeable(ubuf + sk_offset,
- *buf_size - sk_offset);
+ ret = fault_in_pages_writeable(ubuf + fault_offset,
+ *buf_size - fault_offset);
if (ret)
break;
@@ -2256,7 +2262,7 @@ static noinline int search_ioctl(struct inode *inode,
goto err;
}
ret = copy_to_sk(path, &key, sk, buf_size, ubuf,
- &sk_offset, &num_found);
+ &sk_offset, &fault_offset, &num_found);
btrfs_release_path(path);
if (ret)
break;
--
Catalin
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next prev parent reply other threads:[~2021-09-13 14:29 UTC|newest]
Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 16:49 [Ocfs2-devel] [PATCH v7 00/19] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [PATCH v7 02/19] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [RFC][arm64] possible infinite loop in btrfs search_ioctl() Al Viro
2021-08-31 13:54 ` Catalin Marinas [this message]
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
2021-08-29 0:58 ` [Ocfs2-devel] [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable Al Viro
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 06/19] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 07/19] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 08/19] gfs2: Eliminate vestigial HIF_FIRST Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 09/19] gfs2: Remove redundant check from gfs2_glock_dq Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 10/19] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 11/19] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 12/19] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [PATCH v7 13/19] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-27 16:49 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [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 ` [Ocfs2-devel] [PATCH v7 19/19] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-27 17:16 ` [Ocfs2-devel] [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 19:51 ` Andreas Grünbacher
2021-09-03 15:07 ` Filipe Manana
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