[PATCH] binfmt_flat: Fix corruption when not offsetting data start

[Palmer Dabbelt]

On Wed, 24 Apr 2024 13:44:31 PDT (-0700), alex at ghiti.fr wrote:
> Hi Stefan,
>
> On 26/03/2024 04:20, Stefan O'Rear wrote:
>> Commit 04d82a6d0881 ("binfmt_flat: allow not offsetting data start")
>> introduced a RISC-V specific variant of the FLAT format which does not
>> allocate any space for the (obsolescent) array of shared library
>> pointers. However, it did not disable the code which initializes the
>> array, resulting in the corruption of sizeof(long) bytes before the DATA
>> segment, generally the end of the TEXT segment.
>>
>> Use CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET to guard initialization the
>> shared library pointer region so that it will only be initialized if
>> space is reserved for it.
>>
>> Fixes: 04d82a6d0881 ("binfmt_flat: allow not offsetting data start")
>> Signed-off-by: Stefan O'Rear <sorear at fastmail.com>
>> Tested-by: Waldemar Brodkorb <wbx at openadk.org>
>> ---
>>   fs/binfmt_flat.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
>> index c26545d71d39..70c2b68988f4 100644
>> --- a/fs/binfmt_flat.c
>> +++ b/fs/binfmt_flat.c
>> @@ -879,6 +879,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
>>   	if (res < 0)
>>   		return res;
>>
>> +#ifndef CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET
>>   	/* Update data segment pointers for all libraries */
>>   	for (i = 0; i < MAX_SHARED_LIBS; i++) {
>>   		if (!libinfo.lib_list[i].loaded)
>> @@ -893,6 +894,7 @@ static int load_flat_binary(struct linux_binprm *bprm)
>>   				return -EFAULT;
>>   		}
>>   	}
>> +#endif
>>
>>   	set_binfmt(&flat_format);
>>
>
> I have this fix on my list for quite some time, will you respin a new
> version for 6.9?

IIRC we asked on IRC and Sorear wasn't going to respin the patch, so 
unless someone else wants to pick it up I think it's just going to get 
lost.

>
> Thanks,
>
> Alex