On Fri, Jul 6, 2018 at 12:13 AM, Oscar Salvador
<osalvador@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Jul 05, 2018 at 08:44:18AM -0700, Kees Cook wrote:
>> On Thu, Jul 5, 2018 at 7:55 AM, <osalvador@xxxxxxxxxxxxxxxxxx> wrote:
>> > From: Oscar Salvador <osalvador@xxxxxxx>
>> >
>> > The current code does not make sure to page align bss before calling
>> > vm_brk(), and this can lead to a VM_BUG_ON() in __mm_populate()
>> > due to the requested lenght not being correctly aligned.
>> >
>> > Let us make sure to align it properly.
>> >
>> > Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
>> > Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>> > Reported-by: syzbot+5dcb560fe12aa5091c06@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> Wow. CONFIG_USELIB? I'm surprised distros are still using this. 32-bit
>> only, and libc5 and earlier only.
>>
>> Regardless, this appears to match the current bss alignment logic in
>> the main elf loader, so:
>>
>> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
>>
>> -Kees
>>
>> > ---
>> > fs/binfmt_elf.c | 5 ++---
>> > 1 file changed, 2 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
>> > index 0ac456b52bdd..816cc921cf36 100644
>> > --- a/fs/binfmt_elf.c
>> > +++ b/fs/binfmt_elf.c
>> > @@ -1259,9 +1259,8 @@ static int load_elf_library(struct file *file)
>> > goto out_free_ph;
>> > }
>> >
>> > - len = ELF_PAGESTART(eppnt->p_filesz + eppnt->p_vaddr +
>> > - ELF_MIN_ALIGN - 1);
>> > - bss = eppnt->p_memsz + eppnt->p_vaddr;
>> > + len = ELF_PAGEALIGN(eppnt->p_filesz + eppnt->p_vaddr);
>> > + bss = ELF_PAGEALIGN(eppnt->p_memsz + eppnt->p_vaddr);
>> > if (bss > len) {
>> > error = vm_brk(len, bss - len);
>> > if (error)
>> > --
>> > 2.13.6
>> >
> CC Andrew
>
> Hi Andrew,
>
> in case this patch gets accepted, does it have to go through your tree?
> Or is it for someone else to take it?
(FWIW, binfmt_elf changes have traditionally gone through -mm, yes.)
-Kees
--
Kees Cook
Pixel Security
