Re: [PATCH v4] tools/mm: Fix slabinfo crash when MAX_SLABS is exceeded

[Vlastimil Babka <vbabka@suse.cz>]

On 10/31/24 11:55, Marc Dionne wrote:
> From: Marc Dionne <marc.dionne@auristor.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@auristor.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  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..1a9b807a48c3 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 2000
>  #define MAX_ALIASES 500
>  #define MAX_NODES 1024
>  
> @@ -1228,6 +1228,8 @@ static void read_slab_dir(void)
>  				continue;
>  		switch (de->d_type) {
>  		   case DT_LNK:
> +			if (alias - aliasinfo == MAX_ALIASES)
> +				fatal("Too many aliases\n");
>  			alias->name = strdup(de->d_name);
>  			count = readlink(de->d_name, buffer, sizeof(buffer)-1);
>  
> @@ -1242,6 +1244,8 @@ static void read_slab_dir(void)
>  			alias++;
>  			break;
>  		   case DT_DIR:
> +			if (slab - slabinfo == MAX_SLABS)
> +				fatal("Too many slabs\n");
>  			if (chdir(de->d_name))
>  				fatal("Unable to access slab %s\n", slab->name);
>  			slab->name = strdup(de->d_name);
> @@ -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)