Re: [PATCH] init/main.c: Fix potential static_command_line memory overflow

[Mike Rapoport <rppt@kernel.org>]

On Thu, Apr 11, 2024 at 09:23:47AM +0200, Geert Uytterhoeven wrote:
> CC Hiramatsu-san
> 
> On Thu, Apr 11, 2024 at 5:25 AM Yuntao Wang <ytcoode@gmail.com> wrote:
> > We allocate memory of size 'xlen + strlen(boot_command_line) + 1' for
> > static_command_line, but the strings copied into static_command_line are
> > extra_command_line and command_line, rather than extra_command_line and
> > boot_command_line.
> >
> > When strlen(command_line) > strlen(boot_command_line), static_command_line
> > will overflow.

Can this ever happen? 
Did you observe the overflow or is this a theoretical bug?

> > Fixes: f5c7310ac73e ("init/main: add checks for the return value of memblock_alloc*()")

f5c7310ac73e didn't have the logic for calculating allocation size, we
surely don't want to go back that far wiht Fixes.

> > Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
> > ---
> >  init/main.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/init/main.c b/init/main.c
> > index 2ca52474d0c3..a7b1f5f3e3b6 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -625,11 +625,13 @@ static void __init setup_command_line(char *command_line)
> >         if (extra_init_args)
> >                 ilen = strlen(extra_init_args) + 4; /* for " -- " */
> >
> > -       len = xlen + strlen(boot_command_line) + 1;
> > +       len = xlen + strlen(boot_command_line) + ilen + 1;
> >
> > -       saved_command_line = memblock_alloc(len + ilen, SMP_CACHE_BYTES);
> > +       saved_command_line = memblock_alloc(len, SMP_CACHE_BYTES);
> >         if (!saved_command_line)
> > -               panic("%s: Failed to allocate %zu bytes\n", __func__, len + ilen);
> > +               panic("%s: Failed to allocate %zu bytes\n", __func__, len);
> > +
> > +       len = xlen + strlen(command_line) + 1;
> >
> >         static_command_line = memblock_alloc(len, SMP_CACHE_BYTES);
> >         if (!static_command_line)
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds

-- 
Sincerely yours,
Mike.