Re: [PATCH 2/2] exec: increase BINPRM_BUF_SIZE to 256

[Kees Cook <keescook@chromium.org>]

On Mon, Nov 12, 2018 at 5:52 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Mon, 12 Nov 2018 17:09:56 +0100 Oleg Nesterov <oleg@redhat.com> wrote:
>
>> Large enterprise clients often times run applications out of networked
>> file systems where the IT mandated layout of project volumes can end up
>> leading to paths that are longer than 128 characters. Bumping this up to
>> the next order of two solves this problem in all but the most egregious
>> case while still fitting into a 512b slab.
>>
>> ...
>>
>> --- a/include/uapi/linux/binfmts.h
>> +++ b/include/uapi/linux/binfmts.h
>> @@ -16,6 +16,6 @@ struct pt_regs;
>>  #define MAX_ARG_STRINGS 0x7FFFFFFF
>>
>>  /* sizeof(linux_binprm->buf) */
>> -#define BINPRM_BUF_SIZE 128
>> +#define BINPRM_BUF_SIZE 256

This comment needs updating too:

fs/exec.c: * Check permissions, then read the first 128 (BINPRM_BUF_SIZE) bytes

>>  #endif /* _UAPI_LINUX_BINFMTS_H */
>
> It does seem a rather silly restriction, and it's tempting to suggest
> reworking the code so that linux_binprm.buf is dynamically sized to
> accommodate even ludicrously large strings.
>
> But obviously 128 bytes has been enough for all this time, so that's
> going too far.  However it would be basically cost-free to increase
> BINPRM_BUF_SIZE up to the point where sizeof(struct linux_binprm) ==
> PAGE_SIZE?

Yeah, and this might be a useful detail included in a comment above
the #define...

Regardless:

Acked-by: Kees Cook <keescook@chromium.org>


-- 
Kees Cook