[PATCH 2/6] btrfs-progs: check/original: Do extra verification on file extent item

Qu Wenruo
2019-12-18T01:19:56Z

[BUG]
For certain fuzzed image, `btrfs check` will fail with the following
call trace:
Checking filesystem on issue_213.raw
UUID: 99e50868-0bda-4d89-b0e4-7e8560312ef9
[1/7] checking root items
[2/7] checking extents
Program received signal SIGABRT, Aborted.
0x00007ffff7c88f25 in raise () from /usr/lib/libc.so.6
(gdb) bt
#0 0x00007ffff7c88f25 in raise () from /usr/lib/libc.so.6
#1 0x00007ffff7c72897 in abort () from /usr/lib/libc.so.6
#2 0x00005555555abc3e in run_next_block (...) at check/main.c:6398
#3 0x00005555555b0f36 in deal_root_from_list (...) at check/main.c:8408
#4 0x00005555555b1a3d in check_chunks_and_extents (fs_info=0x5555556a1e30) at check/main.c:8690
#5 0x00005555555b1e3e in do_check_chunks_and_extents (fs_info=0x5555556a1e30) a
#6 0x00005555555b5710 in cmd_check (cmd=0x555555696920 <cmd_struct_check>, argc
#7 0x0000555555568dc7 in cmd_execute (cmd=0x555555696920 <cmd_struct_check>, ar
#8 0x0000555555569713 in main (argc=2, argv=0x7fffffffde70) at btrfs.c:386

[CAUSE]
This fuzzed images has a corrupted EXTENT_DATA item in data reloc tree:
item 1 key (256 EXTENT_DATA 256) itemoff 16111 itemsize 12
generation 0 type 2 (prealloc)
prealloc data disk byte 16777216 nr 0
prealloc data offset 0 nr 0

There are several problems with the item:
- Bad item size
12 is too small.
- Bad key offset
offset of EXTENT_DATA type key represents file offset, which should
always be aligned to sector size (4K in this particular case).

[FIX]
Do extra item size and key offset check for original mode, and remove
the abort() call in run_next_block().

And to show off how robust lowmem mode is, lowmem can handle it without
any hiccup.

With this fix, original mode can detect the problem properly:
Checking filesystem on issue_213.raw
UUID: 99e50868-0bda-4d89-b0e4-7e8560312ef9
[1/7] checking root items
[2/7] checking extents
ERROR: invalid file extent item size, have 12 expect (21, 16283]
ERROR: errors found in extent allocation tree or chunk allocation
[3/7] checking free space cache
[4/7] checking fs roots
root 18446744073709551607 root dir 256 error
root 18446744073709551607 inode 256 errors 62, no orphan item, odd file extent, bad file extent
ERROR: errors found in fs roots
found 131072 bytes used, error(s) found
total csum bytes: 0
total tree bytes: 131072
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 124774
file data blocks allocated: 0
referenced 0

Issue: #213
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
check/main.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/check/main.c b/check/main.c
index 08dc9e66..91752dce 100644
--- a/check/main.c
+++ b/check/main.c
@@ -6268,7 +6268,10 @@ static int run_next_block(struct btrfs_root *root,
btree_space_waste += btrfs_leaf_free_space(buf);
for (i = 0; i < nritems; i++) {
struct btrfs_file_extent_item *fi;
+ unsigned long inline_offset;

+ inline_offset = offsetof(struct btrfs_file_extent_item,
+ disk_bytenr);
btrfs_item_key_to_cpu(buf, &key, i);
/*
* Check key type against the leaf owner.
@@ -6384,18 +6387,45 @@ static int run_next_block(struct btrfs_root *root,
}
if (key.type != BTRFS_EXTENT_DATA_KEY)
continue;
+ /* Check itemsize before we continue*/
+ if (btrfs_item_size_nr(buf, i) < inline_offset) {
+ ret = -EUCLEAN;
+ error(
+ "invalid file extent item size, have %u expect (%lu, %lu]",
+ btrfs_item_size_nr(buf, i),
+ inline_offset,
+ BTRFS_LEAF_DATA_SIZE(fs_info));
+ continue;
+ }
fi = btrfs_item_ptr(buf, i,
struct btrfs_file_extent_item);
if (btrfs_file_extent_type(buf, fi) ==
BTRFS_FILE_EXTENT_INLINE)
continue;
+
+ /* Prealloc/regular extent must have fixed item size */
+ if (btrfs_item_size_nr(buf, i) !=
+ sizeof(struct btrfs_file_extent_item)) {
+ ret = -EUCLEAN;
+ error(
+ "invalid file extent item size, have %u expect %zu",
+ btrfs_item_size_nr(buf, i),
+ sizeof(struct btrfs_file_extent_item));
+ continue;
+ }
+ /* key.offset (file offset) must be aligned */
+ if (!IS_ALIGNED(key.offset, fs_info->sectorsize)) {
+ ret = -EUCLEAN;
+ error(
+ "invalid file offset, have %llu expect aligned to %u",
+ key.offset, fs_info->sectorsize);
+ continue;
+ }
if (btrfs_file_extent_disk_bytenr(buf, fi) == 0)
continue;

data_bytes_allocated +=
btrfs_file_extent_disk_num_bytes(buf, fi);
- if (data_bytes_allocated < root->fs_info->sectorsize)
- abort();

data_bytes_referenced +=
btrfs_file_extent_num_bytes(buf, fi);
--
2.24.1