[v2] Correct range checking in mallopt/mxfast/tcache [BZ #25194]

From f5c9a8a75de6d1c114193411634e9abd00618a21 Mon Sep 17 00:00:00 2001
From: DJ Delorie <dj@redhat.com>
Date: Tue, 3 Dec 2019 17:44:36 -0500
Subject: Correct range checking in mallopt/mxfast/tcache [BZ #25194]

do_set_tcache_max, do_set_mxfast:
Fix two instances of comparing "size_t < 0"
Both cases have upper limit, so the "negative value" case
is already handled via overflow semantics.

do_set_tcache_max, do_set_tcache_count:
Fix return value on error.  Note: currently not used.

mallopt:
pass return value of helper functions to user.  Behavior should
only be actually changed for mxfast, where we restore the old
(pre-tunables) behavior.

On 12/4/19 3:58 PM, DJ Delorie wrote:
> 
> From f5c9a8a75de6d1c114193411634e9abd00618a21 Mon Sep 17 00:00:00 2001
> From: DJ Delorie <dj@redhat.com>
> Date: Tue, 3 Dec 2019 17:44:36 -0500
> Subject: Correct range checking in mallopt/mxfast/tcache [BZ #25194]
> 
> do_set_tcache_max, do_set_mxfast:
> Fix two instances of comparing "size_t < 0"
> Both cases have upper limit, so the "negative value" case
> is already handled via overflow semantics.
> 
> do_set_tcache_max, do_set_tcache_count:
> Fix return value on error.  Note: currently not used.
> 
> mallopt:
> pass return value of helper functions to user.  Behavior should
> only be actually changed for mxfast, where we restore the old
> (pre-tunables) behavior.
> 

OK for master with accepted comment changes.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 70cc35a473..a6f78cc6c1 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -5086,13 +5086,14 @@ do_set_arena_max (size_t value)
>  static __always_inline int
>  do_set_tcache_max (size_t value)
>  {
> -  if (value >= 0 && value <= MAX_TCACHE_SIZE)
> +  if (value <= MAX_TCACHE_SIZE)

OK. Removes redundant check detected by static analysis.

>      {
>        LIBC_PROBE (memory_tunable_tcache_max_bytes, 2, value, mp_.tcache_max_bytes);
>        mp_.tcache_max_bytes = value;
>        mp_.tcache_bins = csize2tidx (request2size(value)) + 1;
> +      return 1;

OK.

>      }
> -  return 1;
> +  return 0;

OK.

>  }
>  
>  static __always_inline int
> @@ -5102,8 +5103,9 @@ do_set_tcache_count (size_t value)
>      {
>        LIBC_PROBE (memory_tunable_tcache_count, 2, value, mp_.tcache_count);
>        mp_.tcache_count = value;
> +      return 1;

OK. Success returns 1 (the weird mallopt API)

>      }
> -  return 1;
> +  return 0;


OK. Error returns 0 (the weird mallopt API)

>  }
>  
>  static __always_inline int
> @@ -5119,7 +5121,7 @@ static inline int
>  __always_inline
>  do_set_mxfast (size_t value)
>  {
> -  if (value >= 0 && value <= MAX_FAST_SIZE)
> +  if (value <= MAX_FAST_SIZE)

OK.

>      {
>        LIBC_PROBE (memory_mallopt_mxfast, 2, value, get_max_fast ());
>        set_max_fast (value);
> @@ -5144,18 +5146,25 @@ __libc_mallopt (int param_number, int value)
>       (see definition of set_max_fast).  */
>    malloc_consolidate (av);
>  
> +  /* Many of these helper functions take a size_t.  We do not worry
> +     about overflow here, because forcing a large size_t value to a
> +     negative "int" might be the only way to pass a large size_t value
> +     to mallopt, and because the helpers have sufficient range
> +     checking already despite the conversions.  Many of these helpers
> +     are also referenced in the tunables macros in arena.c.  */

Suggest:

Many of these helper functions take a size_t.  We do not worry
about overflow here, because negative int values will wrap to very
large size_t values and the helpers have sufficient range checking
for such conversions.  Many of these helpers are also used by the
tunables macros from arena.c.


> +
>    switch (param_number)
>      {
>      case M_MXFAST:
> -      do_set_mxfast (value);
> +      res = do_set_mxfast (value);
>        break;
>  
>      case M_TRIM_THRESHOLD:
> -      do_set_trim_threshold (value);
> +      res = do_set_trim_threshold (value);
>        break;
>  
>      case M_TOP_PAD:
> -      do_set_top_pad (value);
> +      res = do_set_top_pad (value);
>        break;
>  
>      case M_MMAP_THRESHOLD:
> @@ -5163,25 +5172,25 @@ __libc_mallopt (int param_number, int value)
>        break;
>  
>      case M_MMAP_MAX:
> -      do_set_mmaps_max (value);
> +      res = do_set_mmaps_max (value);
>        break;
>  
>      case M_CHECK_ACTION:
> -      do_set_mallopt_check (value);
> +      res = do_set_mallopt_check (value);
>        break;
>  
>      case M_PERTURB:
> -      do_set_perturb_byte (value);
> +      res = do_set_perturb_byte (value);
>        break;
>  
>      case M_ARENA_TEST:
>        if (value > 0)
> -	do_set_arena_test (value);
> +	res = do_set_arena_test (value);
>        break;
>  
>      case M_ARENA_MAX:
>        if (value > 0)
> -	do_set_arena_max (value);
> +	res = do_set_arena_max (value);

OK. Awesome fixing all of these to check their return values!

>        break;
>      }
>    __libc_lock_unlock (av->mutex);
>