* [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount
@ 2022-05-24 19:50 Darrick J. Wong
2022-05-24 19:54 ` [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount Darrick J. Wong
2022-05-27 6:20 ` [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Christoph Hellwig
0 siblings, 2 replies; 5+ messages in thread
From: Darrick J. Wong @ 2022-05-24 19:50 UTC (permalink / raw)
To: Eric Sandeen; +Cc: xfs
From: Darrick J. Wong <djwong@kernel.org>
I accidentally tried to xfs_copy an ext4 filesystem, but instead of
rejecting the filesystem, the program instead crashed. I figured out
that zeroing the superblock was enough to trigger this:
# dd if=/dev/zero of=/dev/sda bs=1024k count=1
# xfs_copy /dev/sda /dev/sdb
Floating point exception
The exact crash happens in this line from libxfs_getbuf_flags, which is
called from the main() routine of xfs_copy:
if (btp == btp->bt_mount->m_ddev_targp) {
(*bpp)->b_pag = xfs_perag_get(btp->bt_mount,
xfs_daddr_to_agno(btp->bt_mount, blkno));
The problem here is that the uncached read filled the incore superblock
with zeroes, which means mbuf.sb_agblocks is zero. This causes a
division by zero in xfs_daddr_to_agno, thereby crashing the program.
In commit f8b581d6, we made it so that xfs_buf structures contain a
passive reference to the associated perag structure. That commit
assumes that no program would try a cached buffer read until the buffer
cache is fully set up, which is true throughout xfsprogs... except for
the beginning of xfs_copy. For whatever reason, it attempts an uncached
read of the superblock to figure out the real superblock size, then
performs a *cached* read with the proper buffer length and verifier.
The cached read crashes the program.
Fix the problem by changing the (second) cached read into an uncached read.
Fixes: f8b581d6 ("libxfs: actually make buffers track the per-ag structures")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
copy/xfs_copy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
index 41f594bd..79f65946 100644
--- a/copy/xfs_copy.c
+++ b/copy/xfs_copy.c
@@ -748,7 +748,7 @@ main(int argc, char **argv)
/* Do it again, now with proper length and verifier */
libxfs_buf_relse(sbp);
- error = -libxfs_buf_read(mbuf.m_ddev_targp, XFS_SB_DADDR,
+ error = -libxfs_buf_read_uncached(mbuf.m_ddev_targp, XFS_SB_DADDR,
1 << (sb->sb_sectlog - BBSHIFT), 0, &sbp,
&xfs_sb_buf_ops);
if (error) {
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount
2022-05-24 19:50 [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Darrick J. Wong
@ 2022-05-24 19:54 ` Darrick J. Wong
2022-05-24 23:47 ` Dave Chinner
2022-05-25 4:02 ` Zorro Lang
2022-05-27 6:20 ` [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Christoph Hellwig
1 sibling, 2 replies; 5+ messages in thread
From: Darrick J. Wong @ 2022-05-24 19:54 UTC (permalink / raw)
To: Eric Sandeen, Zorro Lang; +Cc: xfs, fstests
From: Darrick J. Wong <djwong@kernel.org>
This is a regression test for an xfs_copy fix that ensures that it
doesn't perform a cached read of an XFS filesystem prior to initializing
libxfs, since the xfs_mount (and hence the buffer cache) isn't set up
yet.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
tests/xfs/844 | 37 +++++++++++++++++++++++++++++++++++++
tests/xfs/844.out | 3 +++
3 files changed, 40 insertions(+), 1 deletion(-)
create mode 100755 tests/xfs/844
create mode 100644 tests/xfs/844.out
diff --git a/tests/xfs/844 b/tests/xfs/844
new file mode 100755
index 00000000..720f45bb
--- /dev/null
+++ b/tests/xfs/844
@@ -0,0 +1,37 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Oracle. All Rights Reserved.
+#
+# FS QA Test 844
+#
+# Regression test for xfsprogs commit:
+#
+# XXXXXXXX ("xfs_copy: don't use cached buffer reads until after libxfs_mount")
+#
+. ./common/preamble
+_begin_fstest auto copy
+
+_cleanup()
+{
+ cd /
+ rm -r -f $tmp.* $TEST_DIR/$seq.*
+}
+
+# Import common functions.
+# . ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_require_xfs_copy
+_require_test
+
+truncate -s 100m $TEST_DIR/$seq.a
+truncate -s 100m $TEST_DIR/$seq.b
+
+$XFS_COPY_PROG $TEST_DIR/$seq.a $TEST_DIR/$seq.b
+
+# success, all done
+status=0
+exit
diff --git a/tests/xfs/844.out b/tests/xfs/844.out
new file mode 100644
index 00000000..dbefde1c
--- /dev/null
+++ b/tests/xfs/844.out
@@ -0,0 +1,3 @@
+QA output created by 844
+bad magic number
+xfs_copy: couldn't read superblock, error=22
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount
2022-05-24 19:54 ` [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount Darrick J. Wong
@ 2022-05-24 23:47 ` Dave Chinner
2022-05-25 4:02 ` Zorro Lang
1 sibling, 0 replies; 5+ messages in thread
From: Dave Chinner @ 2022-05-24 23:47 UTC (permalink / raw)
To: Darrick J. Wong; +Cc: Eric Sandeen, Zorro Lang, xfs, fstests
On Tue, May 24, 2022 at 12:54:17PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> This is a regression test for an xfs_copy fix that ensures that it
> doesn't perform a cached read of an XFS filesystem prior to initializing
> libxfs, since the xfs_mount (and hence the buffer cache) isn't set up
> yet.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> tests/xfs/844 | 37 +++++++++++++++++++++++++++++++++++++
> tests/xfs/844.out | 3 +++
> 3 files changed, 40 insertions(+), 1 deletion(-)
> create mode 100755 tests/xfs/844
> create mode 100644 tests/xfs/844.out
>
> diff --git a/tests/xfs/844 b/tests/xfs/844
> new file mode 100755
> index 00000000..720f45bb
> --- /dev/null
> +++ b/tests/xfs/844
> @@ -0,0 +1,37 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022 Oracle. All Rights Reserved.
> +#
> +# FS QA Test 844
> +#
> +# Regression test for xfsprogs commit:
> +#
> +# XXXXXXXX ("xfs_copy: don't use cached buffer reads until after libxfs_mount")
> +#
> +. ./common/preamble
> +_begin_fstest auto copy
> +
> +_cleanup()
> +{
> + cd /
> + rm -r -f $tmp.* $TEST_DIR/$seq.*
> +}
Not necessary - $TEST_DIR/$seq.* are sparse files that take up no space.
> +
> +# Import common functions.
> +# . ./common/filter
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs generic
> +_require_xfs_copy
> +_require_test
> +
rm -f $TEST_DIR/$seq.*
To set up known initial state prior to starting the test.
Otherwise looks OK.
Cheers,
Dave.
> +truncate -s 100m $TEST_DIR/$seq.a
> +truncate -s 100m $TEST_DIR/$seq.b
> +
> +$XFS_COPY_PROG $TEST_DIR/$seq.a $TEST_DIR/$seq.b
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/xfs/844.out b/tests/xfs/844.out
> new file mode 100644
> index 00000000..dbefde1c
> --- /dev/null
> +++ b/tests/xfs/844.out
> @@ -0,0 +1,3 @@
> +QA output created by 844
> +bad magic number
> +xfs_copy: couldn't read superblock, error=22
>
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount
2022-05-24 19:54 ` [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount Darrick J. Wong
2022-05-24 23:47 ` Dave Chinner
@ 2022-05-25 4:02 ` Zorro Lang
1 sibling, 0 replies; 5+ messages in thread
From: Zorro Lang @ 2022-05-25 4:02 UTC (permalink / raw)
To: Darrick J. Wong; +Cc: Eric Sandeen, xfs, fstests
On Tue, May 24, 2022 at 12:54:17PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
>
> This is a regression test for an xfs_copy fix that ensures that it
> doesn't perform a cached read of an XFS filesystem prior to initializing
> libxfs, since the xfs_mount (and hence the buffer cache) isn't set up
> yet.
>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> tests/xfs/844 | 37 +++++++++++++++++++++++++++++++++++++
> tests/xfs/844.out | 3 +++
> 3 files changed, 40 insertions(+), 1 deletion(-)
> create mode 100755 tests/xfs/844
> create mode 100644 tests/xfs/844.out
>
> diff --git a/tests/xfs/844 b/tests/xfs/844
> new file mode 100755
> index 00000000..720f45bb
> --- /dev/null
> +++ b/tests/xfs/844
> @@ -0,0 +1,37 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022 Oracle. All Rights Reserved.
> +#
> +# FS QA Test 844
> +#
> +# Regression test for xfsprogs commit:
> +#
> +# XXXXXXXX ("xfs_copy: don't use cached buffer reads until after libxfs_mount")
^^^ I'd like to merge a test after it's fixed offically at first, anyway that
doesn't prevent us from reviewing it at first :)
> +#
> +. ./common/preamble
> +_begin_fstest auto copy
> +
> +_cleanup()
> +{
> + cd /
> + rm -r -f $tmp.* $TEST_DIR/$seq.*
> +}
> +
> +# Import common functions.
> +# . ./common/filter
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
"Modify as appropriate." can be removed.
> +_supported_fs generic
> +_require_xfs_copy
> +_require_test
> +
> +truncate -s 100m $TEST_DIR/$seq.a
> +truncate -s 100m $TEST_DIR/$seq.b
fstests recommends using "truncate" of XFS_IO_PROG, although use 'truncate'
isn't wrong at here.
As TEST_DIR might have existed files, do we need to do
rm -rf $TEST_DIR/$seq.a $TEST_DIR/$seq.b
at first?
Thanks,
Zorro
> +
> +$XFS_COPY_PROG $TEST_DIR/$seq.a $TEST_DIR/$seq.b
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/xfs/844.out b/tests/xfs/844.out
> new file mode 100644
> index 00000000..dbefde1c
> --- /dev/null
> +++ b/tests/xfs/844.out
> @@ -0,0 +1,3 @@
> +QA output created by 844
> +bad magic number
> +xfs_copy: couldn't read superblock, error=22
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount
2022-05-24 19:50 [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Darrick J. Wong
2022-05-24 19:54 ` [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount Darrick J. Wong
@ 2022-05-27 6:20 ` Christoph Hellwig
1 sibling, 0 replies; 5+ messages in thread
From: Christoph Hellwig @ 2022-05-27 6:20 UTC (permalink / raw)
To: Darrick J. Wong; +Cc: Eric Sandeen, xfs
Looks good:
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-05-27 6:20 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-05-24 19:50 [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Darrick J. Wong
2022-05-24 19:54 ` [PATCH] xfs: test xfs_copy doesn't do cached read before libxfs_mount Darrick J. Wong
2022-05-24 23:47 ` Dave Chinner
2022-05-25 4:02 ` Zorro Lang
2022-05-27 6:20 ` [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Christoph Hellwig
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.