Re: [PATCH] check: check so offset is not bigger then the leaf

Trollkarlen Marklund
2015-06-29T11:16:30Z

> On 18 Jun 2015, at 19:44, David Sterba <dsterba@suse.cz> wrote:
>
> On Thu, Jun 18, 2015 at 01:59:13AM +0200, Robert Marklund wrote:
>> This could crash before because of dangerous dangling
>> offset of pointer.
>
> That's right, this can happen. There are more btrfs_item_ptr that would
> be good to validate that way, namely in the checker as it's most likely
> to see corrupted data.
>
> I think it's worth to add a wrapper macro for that, that would be like
>
> (int) btrfs_item_ptr_validate(ei, leaf, slot, struct ..., *optional_key)
>
> and return 0 if it's ok, 1 if there's a problem and prints the details.
>
>> Signed-off-by: Robert Marklund <robbelibobban@gmail.com>
>> ---
>> cmds-check.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/cmds-check.c b/cmds-check.c
>> index 778f141..da36758 100644
>> --- a/cmds-check.c
>> +++ b/cmds-check.c
>> @@ -8906,6 +8906,16 @@ static int build_roots_info_cache(struct btrfs_fs_info *info)
>> goto next;
>>
>> ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
>> +
>> + if ((long long)ei > info->extent_root->leafsize) {
>> + fprintf(stderr, "Bad leaf = %p, slot = %d\n", leaf, slot);
>> + fprintf(stderr, "item ptr = %p\n", ei);
>> + fprintf(stderr, "objectid = %llx\n", found_key.objectid);
>> + fprintf(stderr, "type = %x\n", found_key.type);
>> + fprintf(stderr, "offset = %llx\n", found_key.offset);
>
> Hm, I'm not sure whether to continue or fail at this point.
>

Im not either :)
But for me its better to keep trying until you hot the wall for real.

> Do you have a crafted filesystem image that can reproduce that or was
> that found by code inspection?

I have a failed filesystem caused by a failing disk that I tried to fix/recover.
Then i stumbled on this, and later on on some more places other then this.
Ill submit that also and in a nicer way when my filesystem is rescued.

>
>> + goto next;
>> + }
>> +
>> flags = btrfs_extent_flags(leaf, ei);
>>
>> if (found_key.type == BTRFS_EXTENT_ITEM_KEY &&