malloc: make malloc fail with requests larger than PTRDIFF_MAX (BZ#23741)

As discussed previously on libc-alpha [1], this patch follows up the idea
and add both the __attribute_alloc_size__ on malloc functions (malloc,
calloc, realloc, reallocarray, valloc, pvalloc, and memalign) and limit
maximum requested allocation size to up PTRDIFF_MAX (taking into
consideration internal padding and alignment).

This aligns glibc with gcc expected size defined by default warning
-Walloc-size-larger-than value which warns for allocation larger than
PTRDIFF_MAX.  It also aligns with gcc expectation regarding libc and
expected size, such as described in PR#67999 [2] and previously discussed
ISO C11 issues [3] on libc-alpha.

From the RFC thread [4] and previous discussion, it seems that consensus
is only to limit such requested size for malloc functions, not the system
allocation one (mmap, sbrk, etc.).

The implementation changes checked_request2size to check for both overflow
and maximum object size up to PTRDIFF_MAX. No additional checks are done
on sysmalloc, so it can still issue mmap with values larger than
PTRDIFF_T depending on the requested size.

The __attribute_alloc_size__ is for functions that return a pointer only,
which means it cannot be applied to posix_memalign (see remarks in GCC
PR#87683 [5]). The runtimes checks to limit maximum requested allocation
size does applies to posix_memalign.

Checked on x86_64-linux-gnu and i686-linux-gnu.

[1] https://sourceware.org/ml/libc-alpha/2018-11/msg00223.html
[2] https://gcc.gnu.org/bugzilla//show_bug.cgi?id=67999
[3] https://sourceware.org/ml/libc-alpha/2011-12/msg00066.html
[4] https://sourceware.org/ml/libc-alpha/2018-11/msg00224.html
[5] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87683

	[BZ #23741]
	* malloc/hooks.c (malloc_check, realloc_check): Use
	__builtin_add_overflow on overflow check and adapt to
	checked_request2size change.
	* malloc/malloc.c (__libc_malloc, __libc_realloc, _mid_memalign,
	__libc_pvalloc, __libc_calloc, _int_memalign): Limit maximum
	allocation size to PTRDIFF_MAX.
	(REQUEST_OUT_OF_RANGE): Remove macro.
	(checked_request2size): Change to inline function and limit maximum
	requested size to PTRDIFF_MAX.
	(__libc_malloc, __libc_realloc, _int_malloc, _int_memalign): Limit
	maximum allocation size to PTRDIFF_MAX.
	(_mid_memalign): Use _int_memalign call for overflow check.
	(__libc_pvalloc): Use __builtin_add_overflow on overflow check.
	(__libc_calloc): Use __builtin_mul_overflow for overflow check and
	limit maximum requested size to PTRDIFF_MAX.
	* malloc/malloc.h (malloc, calloc, realloc, reallocarray, memalign,
	valloc, pvalloc): Add __attribute_alloc_size__.
	* stdlib/stdlib.h (malloc, realloc, reallocarray, valloc): Likewise.
	* malloc/tst-malloc-too-large.c (do_test): Add check for allocation
	larger than PTRDIFF_MAX.
	* malloc/tst-memalign.c (do_test): Disable -Walloc-size-larger-than=
	around tests of malloc with negative sizes.
	* malloc/tst-posix_memalign.c (do_test): Likewise.
	* malloc/tst-pvalloc.c (do_test): Likewise.
	* malloc/tst-valloc.c (do_test): Likewise.
	* malloc/tst-reallocarray.c (do_test): Replace call to reallocarray
	with resulting size allocation larger than PTRDIFF_MAX with
	reallocarray_nowarn.
	(reallocarray_nowarn): New function.
	* NEWS: Mention the malloc function semantic change.

1 files changed, 10 insertions, 7 deletions

diff --git a/malloc/hooks.c b/malloc/hooks.c
index 4678973..b7a453f 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -226,8 +226,9 @@ static void *
 malloc_check (size_t sz, const void *caller)
 {
   void *victim;
+  size_t nb;
 
-  if (sz + 1 == 0)
+  if (__builtin_add_overflow (sz, 1, &nb))
     {
       __set_errno (ENOMEM);
       return NULL;
@@ -235,7 +236,7 @@ malloc_check (size_t sz, const void *caller)
 
   __libc_lock_lock (main_arena.mutex);
   top_check ();
-  victim = _int_malloc (&main_arena, sz + 1);
+  victim = _int_malloc (&main_arena, nb);
   __libc_lock_unlock (main_arena.mutex);
   return mem2mem_check (victim, sz);
 }
@@ -268,8 +269,9 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
   INTERNAL_SIZE_T nb;
   void *newmem = 0;
   unsigned char *magic_p;
+  size_t rb;
 
-  if (bytes + 1 == 0)
+  if (__builtin_add_overflow (bytes, 1, &rb))
     {
       __set_errno (ENOMEM);
       return NULL;
@@ -289,7 +291,9 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
     malloc_printerr ("realloc(): invalid pointer");
   const INTERNAL_SIZE_T oldsize = chunksize (oldp);
 
-  checked_request2size (bytes + 1, nb);
+  if (!checked_request2size (rb, &nb))
+    goto invert;
+
   __libc_lock_lock (main_arena.mutex);
 
   if (chunk_is_mmapped (oldp))
@@ -308,7 +312,7 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
           {
             /* Must alloc, copy, free. */
 	    top_check ();
-	    newmem = _int_malloc (&main_arena, bytes + 1);
+	    newmem = _int_malloc (&main_arena, rb);
             if (newmem)
               {
                 memcpy (newmem, oldmem, oldsize - 2 * SIZE_SZ);
@@ -320,8 +324,6 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
   else
     {
       top_check ();
-      INTERNAL_SIZE_T nb;
-      checked_request2size (bytes + 1, nb);
       newmem = _int_realloc (&main_arena, oldp, oldsize, nb);
     }
 
@@ -334,6 +336,7 @@ realloc_check (void *oldmem, size_t bytes, const void *caller)
   /* mem2chunk_check changed the magic byte in the old chunk.
      If newmem is NULL, then the old chunk will still be used though,
      so we need to invert that change here.  */
+invert:
   if (newmem == NULL)
     *magic_p ^= 0xFF;
   DIAG_POP_NEEDS_COMMENT;