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

[Yuntao Wang <ytcoode@gmail.com>]

On Thu, 11 Apr 2024 16:21:37 +0300, Mike Rapoport <rppt@kernel.org> wrote:
> 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?

I didn't observe the overflow, it's just 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.

Before commit f5c7310ac73e, the memory size allocated for static_command_line
was 'strlen(command_line) + 1', but commit f5c7310ac73e changed this size
to 'strlen(boot_command_line) + 1'. I think this should be wrong.

> > > 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.