Re: [PATCH v2] powerpc/64: Fix build failure with GCC 8.1

[Christophe LEROY]

Le 29/05/2018 Ã 09:47, Geert Uytterhoeven a ÃcritÂ:
> Hi Christophe,
>
> CC Geoff
>
> On Tue, May 29, 2018 at 8:03 AM, Christophe Leroy
> <christophe.leroy@xxxxxx> wrote:
> >    CC      arch/powerpc/kernel/nvram_64.o
> > arch/powerpc/kernel/nvram_64.c: In function 'nvram_create_partition':
> > arch/powerpc/kernel/nvram_64.c:1042:2: error: 'strncpy' specified bound 12 equals destination size [-Werror=stringop-truncation]
> >    strncpy(new_part->header.name, name, 12);
> >    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> >    CC      arch/powerpc/kernel/trace/ftrace.o
> > In function 'make_field',
> >      inlined from 'ps3_repository_read_boot_dat_address' at arch/powerpc/platforms/ps3/repository.c:900:9:
> > arch/powerpc/platforms/ps3/repository.c:106:2: error: 'strncpy' output truncated before terminating nul copying 8 bytes from a string of the same length [-Werror=stringop-truncation]
> >    strncpy((char *)&n, text, 8);
> >    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
>
> Thanks for your patch!
>
> > --- a/arch/powerpc/kernel/nvram_64.c
> > +++ b/arch/powerpc/kernel/nvram_64.c
> > @@ -1039,7 +1039,7 @@ loff_t __init nvram_create_partition(const char *name, int sig,
> >          new_part->index = free_part->index;
> >          new_part->header.signature = sig;
> >          new_part->header.length = size;
> > -       strncpy(new_part->header.name, name, 12);
> > +       memcpy(new_part->header.name, name, strnlen(name, sizeof(new_part->header.name)));
>
> The comment for nvram_header.lgnth says:
>
>          /* Terminating null required only for names < 12 chars. */
>
> This will not terminate the string with a zero (the struct is
> allocated with kmalloc).
> So the original code is correct, the new one isn't.

Right, then I have to first zeroize the destination.

> >          new_part->header.checksum = nvram_checksum(&new_part->header);
> >
> >          rc = nvram_write_header(new_part);
> > diff --git a/arch/powerpc/platforms/ps3/repository.c b/arch/powerpc/platforms/ps3/repository.c
> > index 50dbaf24b1ee..e49c887787c4 100644
> > --- a/arch/powerpc/platforms/ps3/repository.c
> > +++ b/arch/powerpc/platforms/ps3/repository.c
> > @@ -101,9 +101,9 @@ static u64 make_first_field(const char *text, u64 index)
> >
> >   static u64 make_field(const char *text, u64 index)
> >   {
> > -       u64 n;
> > +       u64 n = 0;
> >
> > -       strncpy((char *)&n, text, 8);
> > +       memcpy((char *)&n, text, strnlen(text, sizeof(n)));
>
> This changes behavior: strncpy() fills the remainder of the buffer with
> zeroes.  I don't remember the details of the PS3 repository structure,
> but given this writes to a fixed size u64 buffer, I'd expect the PS3
> hypervisor code to (1) rely on the zero padding, and (2) not need a zero
> terminator if there are 8 characters in the buffer, so probably the
> original code is correct, and the "fixed" code isn't.

Here I have set n to 0 prior to the copy, so the buffer IS zero padded.

Christophe

> Has this been tested on a PS3?
>
> >          return n + index;
> >   }
>
> Gr{oetje,eeting}s,
>
>                          Geert