Btrfs: incremental send, fix file corruption when no-holes feature is enabled
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Message ID 20190520085542.29282-1-fdmanana@kernel.org
State New
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Series
  • Btrfs: incremental send, fix file corruption when no-holes feature is enabled
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Commit Message

Filipe Manana May 20, 2019, 8:55 a.m. UTC
From: Filipe Manana <fdmanana@suse.com>

When using the no-holes feature, if we have a file with prealloc extents
with a start offset beyond the file's eof, doing an incremental send can
cause corruption of the file due to incorrect hole detection. Such case
requires that the prealloc extent(s) exist in both the parent and send
snapshots, and that a hole is punched into the file that covers all its
extents that do not cross the eof boundary.

Example reproducer:

  $ mkfs.btrfs -f -O no-holes /dev/sdb
  $ mount /dev/sdb /mnt/sdb

  $ xfs_io -f -c "pwrite -S 0xab 0 500K" /mnt/sdb/foobar
  $ xfs_io -c "falloc -k 1200K 800K" /mnt/sdb/foobar

  $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/base

  $ btrfs send -f /tmp/base.snap /mnt/sdb/base

  $ xfs_io -c "fpunch 0 500K" /mnt/sdb/foobar

  $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/incr

  $ btrfs send -p /mnt/sdb/base -f /tmp/incr.snap /mnt/sdb/incr

  $ md5sum /mnt/sdb/incr/foobar
  816df6f64deba63b029ca19d880ee10a   /mnt/sdb/incr/foobar

  $ mkfs.btrfs -f /dev/sdc
  $ mount /dev/sdc /mnt/sdc

  $ btrfs receive -f /tmp/base.snap /mnt/sdc
  $ btrfs receive -f /tmp/incr.snap /mnt/sdc

  $ md5sum /mnt/sdc/incr/foobar
  cf2ef71f4a9e90c2f6013ba3b2257ed2   /mnt/sdc/incr/foobar

    --> Different checksum, because the prealloc extent beyond the
        file's eof confused the hole detection code and it assumed
        a hole starting at offset 0 and ending at the offset of the
        prealloc extent (1200Kb) instead of ending at the offset
        500Kb (the file's size).

Fix this by ensuring we never cross the file's size when issuing the
write operations for a hole.

Fixes: 16e7549f045d33 ("Btrfs: incompatible format change to remove hole extents")
CC: stable@vger.kernel.org # 3.14+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/send.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Sasha Levin May 20, 2019, 1:58 p.m. UTC | #1
Hi,

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag,
fixing commit: 16e7549f045d Btrfs: incompatible format change to remove hole extents.

The bot has tested the following trees: v5.1.3, v5.0.17, v4.19.44, v4.14.120, v4.9.177, v4.4.180, v3.18.140.

v5.1.3: Build OK!
v5.0.17: Build OK!
v4.19.44: Build OK!
v4.14.120: Failed to apply! Possible dependencies:
    22d3151c2c4c ("Btrfs: send, fix incorrect file layout after hole punching beyond eof")

v4.9.177: Failed to apply! Possible dependencies:
    22d3151c2c4c ("Btrfs: send, fix incorrect file layout after hole punching beyond eof")

v4.4.180: Failed to apply! Possible dependencies:
    22d3151c2c4c ("Btrfs: send, fix incorrect file layout after hole punching beyond eof")

v3.18.140: Failed to apply! Possible dependencies:
    22d3151c2c4c ("Btrfs: send, fix incorrect file layout after hole punching beyond eof")


How should we proceed with this patch?

--
Thanks,
Sasha
David Sterba May 27, 2019, 3:21 p.m. UTC | #2
On Mon, May 20, 2019 at 09:55:42AM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> When using the no-holes feature, if we have a file with prealloc extents
> with a start offset beyond the file's eof, doing an incremental send can
> cause corruption of the file due to incorrect hole detection. Such case
> requires that the prealloc extent(s) exist in both the parent and send
> snapshots, and that a hole is punched into the file that covers all its
> extents that do not cross the eof boundary.
> 
> Example reproducer:
> 
>   $ mkfs.btrfs -f -O no-holes /dev/sdb
>   $ mount /dev/sdb /mnt/sdb
> 
>   $ xfs_io -f -c "pwrite -S 0xab 0 500K" /mnt/sdb/foobar
>   $ xfs_io -c "falloc -k 1200K 800K" /mnt/sdb/foobar
> 
>   $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/base
> 
>   $ btrfs send -f /tmp/base.snap /mnt/sdb/base
> 
>   $ xfs_io -c "fpunch 0 500K" /mnt/sdb/foobar
> 
>   $ btrfs subvolume snapshot -r /mnt/sdb /mnt/sdb/incr
> 
>   $ btrfs send -p /mnt/sdb/base -f /tmp/incr.snap /mnt/sdb/incr
> 
>   $ md5sum /mnt/sdb/incr/foobar
>   816df6f64deba63b029ca19d880ee10a   /mnt/sdb/incr/foobar
> 
>   $ mkfs.btrfs -f /dev/sdc
>   $ mount /dev/sdc /mnt/sdc
> 
>   $ btrfs receive -f /tmp/base.snap /mnt/sdc
>   $ btrfs receive -f /tmp/incr.snap /mnt/sdc
> 
>   $ md5sum /mnt/sdc/incr/foobar
>   cf2ef71f4a9e90c2f6013ba3b2257ed2   /mnt/sdc/incr/foobar
> 
>     --> Different checksum, because the prealloc extent beyond the
>         file's eof confused the hole detection code and it assumed
>         a hole starting at offset 0 and ending at the offset of the
>         prealloc extent (1200Kb) instead of ending at the offset
>         500Kb (the file's size).
> 
> Fix this by ensuring we never cross the file's size when issuing the
> write operations for a hole.
> 
> Fixes: 16e7549f045d33 ("Btrfs: incompatible format change to remove hole extents")
> CC: stable@vger.kernel.org # 3.14+
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Queued for 5.2-rc, thanks.

Patch
diff mbox series

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index c5184691d7f2..1549d0639b57 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -4999,6 +4999,12 @@  static int send_hole(struct send_ctx *sctx, u64 end)
 	if (offset >= sctx->cur_inode_size)
 		return 0;
 
+	/*
+	 * Don't go beyond the inode's i_size due to prealloc extents that start
+	 * after the i_size.
+	 */
+	end = min_t(u64, end, sctx->cur_inode_size);
+
 	if (sctx->flags & BTRFS_SEND_FLAG_NO_FILE_DATA)
 		return send_update_extent(sctx, offset, end - offset);