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get_new_location() uses BUG_ON() to crash the kernel if the file extent
item it looks up has any of offset, compression, encryption, or
other_encoding set non-zero. The data reloc inode is only written by
relocation's own paths and the four fields are always 0 in what the
kernel writes:
- insert_prealloc_file_extent() memsets the stack item to zero and
only fills in type, disk_bytenr, disk_num_bytes and num_bytes, so
offset/compression/encryption/other_encoding stay 0.
- insert_ordered_extent_file_extent() copies oe->compress_type into
the file extent's compression field, but the data reloc inode is
created with BTRFS_INODE_NOCOMPRESS so compress_type is always 0;
encryption and other_encoding are reserved-and-zero in btrfs.
A non-zero value here means the leaf decoded from disk does not match
what the kernel wrote, i.e. on-disk corruption. A malformed image
reaches this code via balance and panics the kernel.
A previous attempt to enforce all four constraints in tree-checker's
check_extent_data_item() was merged as commit 7d0ee95979e9 ("btrfs:
validate data reloc tree file extent item members in tree-checker")
and then reverted by commit 1c034697fcaa after btrfs/061 produced
false positives on arm64 with 64K pages. The reason: relocation
writeback legitimately produces REG file_extent_items with offset != 0
in the data reloc tree. When an ordered extent covers only the back
portion of an underlying PREALLOC (num_bytes < ram_bytes on the input
file_extent), insert_ordered_extent_file_extent() inserts a REG with
offset = oe->offset
num_bytes = oe->num_bytes
ram_bytes preserved from the original PREALLOC,
and this item can reach disk if a transaction commit fires while it
is present in the leaf.
The four fields belong in different layers:
- compression, encryption and other_encoding are universal
invariants for every item in the data reloc tree, regardless of
cluster geometry. Enforce them in tree-checker's
check_extent_data_item() so a corrupt leaf is rejected at read
time.
- offset is only an invariant at the cluster-boundary keys that
get_new_location() searches (the key is computed as
src_disk_bytenr - reloc_block_group_start). Partial-PREALLOC
writebacks legitimately place REG items at non-boundary keys with
offset != 0; tree-checker cannot reject these. The cluster-
boundary item is always written by either
insert_prealloc_file_extent() (offset=0 by memset) or by the
front portion of a partial writeback (offset=0 by construction),
so a non-zero offset there is corruption.
Enforce the universal invariants in check_extent_data_item() with a
file_extent_err() rejection. Convert the BUG_ON() in
get_new_location() to a -EUCLEAN return paired with btrfs_print_leaf()
and btrfs_err() so the offending leaf is logged. The caller in
replace_file_extents() already handles non-zero returns from
get_new_location() by breaking out of the loop without aborting the
transaction.
Suggested-by: Qu Wenruo <wqu@suse.com>
Suggested-by: David Sterba <dsterba@suse.com>
Reported-by: syzbot+3e20d8f3d41bac5dc9a2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3e20d8f3d41bac5dc9a2
Signed-off-by: Teng Liu <27rabbitlt@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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| init | ||
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| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
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| .gitattributes | ||
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| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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