linux-kernel - Re: [PATCH 1/2] vsprintf: Prevent crash when dereferencing invalid pointers for %pD

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Message-ID: <CAHp75VcR1rJ5AX_Nj3n2NnMasLRp74Y3R6Mh4XQ5s64aKrF6tw@mail.gmail.com>
Date:   Fri, 9 Aug 2019 13:51:57 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jia He <justin.he@....com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Tobin C. Harding" <tobin@...nel.org>
Subject: Re: [PATCH 1/2] vsprintf: Prevent crash when dereferencing invalid
 pointers for %pD

On Fri, Aug 9, 2019 at 4:28 AM Jia He <justin.he@....com> wrote:
>
> Commit 3e5903eb9cff ("vsprintf: Prevent crash when dereferencing invalid
> pointers") prevents most crash except for %pD.
> There is an additional pointer dereferencing before dentry_name.
>
> At least, vma->file can be NULL and be passed to printk %pD in
> print_bad_pte, which can cause crash.
>
> This patch fixes it with introducing a new file_dentry_name.
>

Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>

Perhaps you need to add a Fixes tag

> Signed-off-by: Jia He <justin.he@....com>
> ---
>  lib/vsprintf.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 63937044c57d..b4a119176fdb 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -869,6 +869,15 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp
>         return widen_string(buf, n, end, spec);
>  }
>
> +static noinline_for_stack
> +char *file_dentry_name(char *buf, char *end, const struct file *f,
> +                       struct printf_spec spec, const char *fmt)
> +{
> +       if (check_pointer(&buf, end, f, spec))
> +               return buf;
> +
> +       return dentry_name(buf, end, f->f_path.dentry, spec, fmt);
> +}
>  #ifdef CONFIG_BLOCK
>  static noinline_for_stack
>  char *bdev_name(char *buf, char *end, struct block_device *bdev,
> @@ -2166,9 +2175,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>         case 'C':
>                 return clock(buf, end, ptr, spec, fmt);
>         case 'D':
> -               return dentry_name(buf, end,
> -                                  ((const struct file *)ptr)->f_path.dentry,
> -                                  spec, fmt);
> +               return file_dentry_name(buf, end, ptr, spec, fmt);
>  #ifdef CONFIG_BLOCK
>         case 'g':
>                 return bdev_name(buf, end, ptr, spec, fmt);
> --
> 2.17.1
>


-- 
With Best Regards,
Andy Shevchenko