62 lines
2.4 KiB
Diff
62 lines
2.4 KiB
Diff
From baf8a5df8a0c6539818a3f78a68d22648c022e50 Mon Sep 17 00:00:00 2001
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From: "Darrick J. Wong" <djwong@kernel.org>
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Date: Tue, 12 Jul 2022 13:25:33 -0500
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Subject: [PATCH] xfs_copy: don't use cached buffer reads until after
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libxfs_mount
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I accidentally tried to xfs_copy an ext4 filesystem, but instead of
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rejecting the filesystem, the program instead crashed. I figured out
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that zeroing the superblock was enough to trigger this:
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# dd if=/dev/zero of=/dev/sda bs=1024k count=1
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# xfs_copy /dev/sda /dev/sdb
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Floating point exception
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The exact crash happens in this line from libxfs_getbuf_flags, which is
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called from the main() routine of xfs_copy:
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if (btp == btp->bt_mount->m_ddev_targp) {
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(*bpp)->b_pag = xfs_perag_get(btp->bt_mount,
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xfs_daddr_to_agno(btp->bt_mount, blkno));
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The problem here is that the uncached read filled the incore superblock
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with zeroes, which means mbuf.sb_agblocks is zero. This causes a
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division by zero in xfs_daddr_to_agno, thereby crashing the program.
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In commit f8b581d6, we made it so that xfs_buf structures contain a
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passive reference to the associated perag structure. That commit
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assumes that no program would try a cached buffer read until the buffer
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cache is fully set up, which is true throughout xfsprogs... except for
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the beginning of xfs_copy. For whatever reason, it attempts an uncached
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read of the superblock to figure out the real superblock size, then
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performs a *cached* read with the proper buffer length and verifier.
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The cached read crashes the program.
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Fix the problem by changing the (second) cached read into an uncached read.
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Fixes: f8b581d6 ("libxfs: actually make buffers track the per-ag structures")
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Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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Reviewed-by: Dave Chinner <dchinner@redhat.com>
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Reviewed-by: Christoph Hellwig <hch@lst.de>
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Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
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---
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copy/xfs_copy.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
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index 41f594bd..79f65946 100644
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--- a/copy/xfs_copy.c
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+++ b/copy/xfs_copy.c
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@@ -748,7 +748,7 @@ main(int argc, char **argv)
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/* Do it again, now with proper length and verifier */
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libxfs_buf_relse(sbp);
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- error = -libxfs_buf_read(mbuf.m_ddev_targp, XFS_SB_DADDR,
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+ error = -libxfs_buf_read_uncached(mbuf.m_ddev_targp, XFS_SB_DADDR,
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1 << (sb->sb_sectlog - BBSHIFT), 0, &sbp,
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&xfs_sb_buf_ops);
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if (error) {
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--
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2.33.0
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