linux-kernel - Re: [PATCH] tools/mm: Fix slabinfo crash when MAX

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Message-ID: <CAB9dFduUf_3N-9=t3O6ePxanjwPiqdQmgKR6O8VoF5BmPG_b4Q@mail.gmail.com>
Date: Tue, 29 Oct 2024 13:12:59 -0300
From: Marc Dionne <marc.dionne@...istor.com>
To: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools/mm: Fix slabinfo crash when MAX_SLABS is exceeded

On Tue, Oct 29, 2024 at 1:06 PM Marc Dionne <marc.c.dionne@...il.com> wrote:
>
> From: Marc Dionne <marc.dionne@...istor.com>
>
> The number of slabs can easily exceed the hard coded MAX_SLABS in the
> slabinfo tool, causing it to overwrite memory and crash.
>
> Increase the value of MAX_SLABS, and check if that has been exceeded for
> each new slab, instead of at the end when it's already too late.  Also
> move the check for MAX_ALIASES into the loop body.
>
> Signed-off-by: Marc Dionne <marc.dionne@...istor.com>
> ---
>  tools/mm/slabinfo.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/tools/mm/slabinfo.c b/tools/mm/slabinfo.c
> index cfaeaea71042..2c9c86d677ed 100644
> --- a/tools/mm/slabinfo.c
> +++ b/tools/mm/slabinfo.c
> @@ -21,7 +21,7 @@
>  #include <regex.h>
>  #include <errno.h>
>
> -#define MAX_SLABS 500
> +#define MAX_SLABS 1000
>  #define MAX_ALIASES 500
>  #define MAX_NODES 1024
>
> @@ -1240,6 +1240,8 @@ static void read_slab_dir(void)
>                                 p--;
>                         alias->ref = strdup(p);
>                         alias++;
> +                       if (aliases > MAX_ALIASES)

This is not quite right, needs to be alias - aliasinfo.  Will send a V2.

> +                               fatal("Too many aliases\n");
>                         break;
>                    case DT_DIR:
>                         if (chdir(de->d_name))
> @@ -1301,6 +1303,8 @@ static void read_slab_dir(void)
>                         if (slab->name[0] == ':')
>                                 alias_targets++;
>                         slab++;
> +                       if (slab - slabinfo > MAX_SLABS)
> +                               fatal("Too many slabs\n");
>                         break;
>                    default :
>                         fatal("Unknown file type %lx\n", de->d_type);
> @@ -1310,10 +1314,6 @@ static void read_slab_dir(void)
>         slabs = slab - slabinfo;
>         actual_slabs = slabs;
>         aliases = alias - aliasinfo;
> -       if (slabs > MAX_SLABS)
> -               fatal("Too many slabs\n");
> -       if (aliases > MAX_ALIASES)
> -               fatal("Too many aliases\n");
>  }
>
>  static void output_slabs(void)
> --
> 2.47.0
>