Message ID | d5201ee6-ee91-4430-8c20-e1d3d36b7f13@nh2.me |
---|---|
State | New |
Headers | show |
Series | [v2] malloc_stats(): Fix `unsigned int` overflow | expand |
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.
diff --git a/malloc/malloc.c b/malloc/malloc.c index 78a531bc7a..dfb266a226 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -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); }
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(-)