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btrfs-progs: check/lowmem: Fix access on uninitialized memory 

[BUG]
There are some reports on fsck/001 test segfault failure with lowmem mode.

While I failed to reproduce it, valgrind still catches it with the
following output:

  Delete backref in extent [12845056 1048576]
  ERROR: file extent [257, 0] has unaligned disk bytenr: 755944791, should be aligned to 4096
  ERROR: file extent[257 0] root 5 owner 5 backref lost
  Deleted root 5 item[257, 108, 0]
  ==29080== Conditional jump or move depends on uninitialised value(s)
  ==29080==    at 0x1A81D7: btrfs_release_path (ctree.c:97)
  ==29080==    by 0x192C33: repair_extent_data_item (mode-lowmem.c:3330)
  ==29080==    by 0x1962FF: check_leaf_items (mode-lowmem.c:4696)
  ==29080==    by 0x196ABF: walk_down_tree (mode-lowmem.c:4858)
  ==29080==    by 0x197762: check_btrfs_root (mode-lowmem.c:5157)
  ==29080==    by 0x198335: check_chunks_and_extents_lowmem (mode-lowmem.c:5450)
  ==29080==    by 0x166414: do_check_chunks_and_extents (main.c:8829)
  ==29080==    by 0x169CF7: cmd_check (main.c:10313)
  ==29080==    by 0x11CDC6: cmd_execute (commands.h:125)
  ==29080==    by 0x11D712: main (btrfs.c:386)
  ==29080==

[CAUSE]
In repair_extent_data_item() if we find unaligned file extent, we just
delete it and kick in hole punch procedure.

The problem is, file extent deletion is done before initializing @path.
And when the deletion is done without problem, we will goto out tag,
which will release @path, containing uninitialized values, and
triggering segfault.

[FIX]
Don't try to abort trans nor free path if we're going through file
extent deletion routine.

Fixes: 0617bde3bc ("btrfs-progs: lowmem: delete unaligned bytes extent data under repair")
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Qu Wenruo 2020-03-24 11:08:55 +08:00 committed by David Sterba
parent 1311f1b83a
commit 3a2d040070
1 changed files with 2 additions and 1 deletions
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3
check/mode-lowmem.c
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@ -3257,7 +3257,7 @@ static int repair_extent_data_item(struct btrfs_root *root,
ret = delete_item(root, pathp);
if (!ret)
err = 0;
goto out;
goto out_no_release;
}
/* now repair only adds backref */
@ -3332,6 +3332,7 @@ out:
if (trans)
btrfs_commit_transaction(trans, root);
btrfs_release_path(&path);
out_no_release:
if (ret)
error("can't repair root %llu extent data item[%llu %llu]",
root->objectid, disk_bytenr, num_bytes);