[v2] malloc_stats(): Fix `unsigned int` overflow
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Commit Message
Fixes malloc_stats() returning vastly wrong information for programs
that use more than 2 GiB memory.
`man mallinfo` documents that it uses `int` and wraps around, but
`man malloc_stats` does not, and should not.
Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=21556
Signed-off-by: Niklas Hambüchen <mail@nh2.me>
---
malloc/malloc.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
Comments
Niklas Hambchen <mail@nh2.me> writes:
> @@ -5374,7 +5374,7 @@ __malloc_stats (void)
> {
> int i;
> mstate ar_ptr;
> - unsigned int in_use_b = mp_.mmapped_mem, system_b = in_use_b;
> + size_t in_use_b = mp_.mmapped_mem, system_b = in_use_b;
Ok.
> @@ -5389,8 +5389,8 @@ __malloc_stats (void)
> __libc_lock_lock (ar_ptr->mutex);
> int_mallinfo (ar_ptr, &mi);
> fprintf (stderr, "Arena %d:\n", i);
> - fprintf (stderr, "system bytes = %10u\n", (unsigned int) mi.arena);
> - fprintf (stderr, "in use bytes = %10u\n", (unsigned int) mi.uordblks);
> + fprintf (stderr, "system bytes = %10zu\n", mi.arena);
> + fprintf (stderr, "in use bytes = %10zu\n", mi.uordblks);
Ok.
> - fprintf (stderr, "system bytes = %10u\n", system_b);
> - fprintf (stderr, "in use bytes = %10u\n", in_use_b);
> - fprintf (stderr, "max mmap bytes = %10lu\n",
> - (unsigned long) mp_.max_mmapped_mem);
> + fprintf (stderr, "system bytes = %10zu\n", system_b);
> + fprintf (stderr, "in use bytes = %10zu\n", in_use_b);
> + fprintf (stderr, "max mmap bytes = %10zu\n", mp_.max_mmapped_mem);
This needs a cast to (size_t) as max_mmapped_mem is INTERNAL_SIZE_T,
which may be smaller than size_t.
> - fprintf (stderr, "max mmap regions = %10u\n", (unsigned int) mp_.max_n_mmaps);
> + fprintf (stderr, "max mmap regions = %10d\n", mp_.max_n_mmaps);
This causes a negative number to be printed when max_n_mmaps increments
past 2^31, where using "u" defers bad results until 2^32. So IMHO this
one is a regression, not a fix.
> This needs a cast to (size_t) as max_mmapped_mem is INTERNAL_SIZE_T,
> which may be smaller than size_t.
Thanks, will fix!
>> + fprintf (stderr, "max mmap regions = %10d\n", mp_.max_n_mmaps);
>
> This causes a negative number to be printed when max_n_mmaps increments
> past 2^31, where using "u" defers bad results until 2^32. So IMHO this
> one is a regression, not a fix.
I'm not sure I understand:
That statement holds for all `int`s, so following this logic, all `int`s should be casted to `unsigned int` first and printed with `%u`, and `%d` would be quite useless.
Doesn't it make more sense to print an `int` with `%d` as normal, so that you can _see_ in `malloc_stats()` when it overflows?
The non-`malloc_stats()` code that uses the `int` will likely also behave strangely if this overflow happens, so it seems weird to pretend the value is of a different type in the malloc-internals inspection function.
(Besides, `max_n_mmaps` sounds like a count of mmaps, not a byte count, so it should be much less likely to overflow.)
Thanks!
Niklas Hambchen <mail@nh2.me> writes:
>>> + fprintf (stderr, "max mmap regions = %10d\n", mp_.max_n_mmaps);
>>
>> This causes a negative number to be printed when max_n_mmaps increments
>> past 2^31, where using "u" defers bad results until 2^32. So IMHO this
>> one is a regression, not a fix.
>
> I'm not sure I understand:
> That statement holds for all `int`s, so following this logic, all
> `int`s should be casted to `unsigned int` first and printed with `%u`,
> and `%d` would be quite useless.
>
> Doesn't it make more sense to print an `int` with `%d` as normal, so
> that you can _see_ in `malloc_stats()` when it overflows?
It only really overflows when it wraps around 2^32. Until then, the
value is still useful, as long as you present it properly.
An alternative would be to print out "(overflowed)" if the value exceeds 2^31
It just didn't seem right to take something that prints 0..2^32-1 and
reduce it to only print 0..2^31-1.
The other cases were stored as size_t and potentially truncated, which
is a different sort of overflow bug.
@@ -5374,7 +5374,7 @@ __malloc_stats (void)
{
int i;
mstate ar_ptr;
- unsigned int in_use_b = mp_.mmapped_mem, system_b = in_use_b;
+ size_t in_use_b = mp_.mmapped_mem, system_b = in_use_b;
if (!__malloc_initialized)
ptmalloc_init ();
@@ -5389,8 +5389,8 @@ __malloc_stats (void)
__libc_lock_lock (ar_ptr->mutex);
int_mallinfo (ar_ptr, &mi);
fprintf (stderr, "Arena %d:\n", i);
- fprintf (stderr, "system bytes = %10u\n", (unsigned int) mi.arena);
- fprintf (stderr, "in use bytes = %10u\n", (unsigned int) mi.uordblks);
+ fprintf (stderr, "system bytes = %10zu\n", mi.arena);
+ fprintf (stderr, "in use bytes = %10zu\n", mi.uordblks);
#if MALLOC_DEBUG > 1
if (i > 0)
dump_heap (heap_for_ptr (top (ar_ptr)));
@@ -5403,11 +5403,10 @@ __malloc_stats (void)
break;
}
fprintf (stderr, "Total (incl. mmap):\n");
- fprintf (stderr, "system bytes = %10u\n", system_b);
- fprintf (stderr, "in use bytes = %10u\n", in_use_b);
- fprintf (stderr, "max mmap regions = %10u\n", (unsigned int) mp_.max_n_mmaps);
- fprintf (stderr, "max mmap bytes = %10lu\n",
- (unsigned long) mp_.max_mmapped_mem);
+ fprintf (stderr, "system bytes = %10zu\n", system_b);
+ fprintf (stderr, "in use bytes = %10zu\n", in_use_b);
+ fprintf (stderr, "max mmap regions = %10d\n", mp_.max_n_mmaps);
+ fprintf (stderr, "max mmap bytes = %10zu\n", mp_.max_mmapped_mem);
stderr->_flags2 = old_flags2;
_IO_funlockfile (stderr);
}