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malloc: Improve checked_request2size

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Change checked_request2size to return SIZE_MAX for huge inputs.  This
ensures large allocation requests stay large and can't be confused with a
small allocation.  As a result several existing checks against PTRDIFF_MAX
become redundant.

Reviewed-by: DJ Delorie <dj@redhat.com>
This commit is contained in:
Wilco Dijkstra
2025-06-06 17:11:36 +00:00
parent 21fda179c2
commit b68b125ad1
2 changed files with 13 additions and 28 deletions
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4
malloc/malloc-check.c
View File

@@ -275,12 +275,12 @@ realloc_check (void *oldmem, size_t bytes)
malloc_printerr ("realloc(): invalid pointer");
const INTERNAL_SIZE_T oldsize = chunksize (oldp);
chnb = checked_request2size (rb);
if (chnb == 0)
if (rb > PTRDIFF_MAX)
{
__set_errno (ENOMEM);
goto invert;
}
chnb = checked_request2size (rb);
__libc_lock_lock (main_arena.mutex);

37
malloc/malloc.c
View File

@@ -1323,8 +1323,8 @@ nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/* Check if REQ overflows when padded and aligned and if the resulting
value is less than PTRDIFF_T. Returns the requested size or
MINSIZE in case the value is less than MINSIZE, or 0 if any of the
previous checks fail. */
MINSIZE in case the value is less than MINSIZE, or SIZE_MAX if any
of the previous checks fail. */
static __always_inline size_t
checked_request2size (size_t req) __nonnull (1)
{
@@ -1332,7 +1332,7 @@ checked_request2size (size_t req) __nonnull (1)
"PTRDIFF_MAX is not more than half of SIZE_MAX");
if (__glibc_unlikely (req > PTRDIFF_MAX))
return 0;
return SIZE_MAX;
/* When using tagged memory, we cannot share the end of the user
block with the header for the next chunk, so ensure that we
@@ -3462,11 +3462,6 @@ __libc_malloc (size_t bytes)
{
#if USE_TCACHE
size_t nb = checked_request2size (bytes);
if (nb == 0)
{
__set_errno (ENOMEM);
return NULL;
}
if (nb < mp_.tcache_max_bytes)
{
@@ -3611,12 +3606,12 @@ __libc_realloc (void *oldmem, size_t bytes)
|| misaligned_chunk (oldp)))
malloc_printerr ("realloc(): invalid pointer");
nb = checked_request2size (bytes);
if (nb == 0)
if (bytes > PTRDIFF_MAX)
{
__set_errno (ENOMEM);
return NULL;
}
nb = checked_request2size (bytes);
if (chunk_is_mmapped (oldp))
{
@@ -3742,13 +3737,7 @@ _mid_memalign (size_t alignment, size_t bytes)
}
#if USE_TCACHE
size_t nb = checked_request2size (bytes);
if (nb == 0)
{
__set_errno (ENOMEM);
return NULL;
}
void *victim = tcache_get_align (nb, alignment);
void *victim = tcache_get_align (checked_request2size (bytes), alignment);
if (victim != NULL)
return tag_new_usable (victim);
#endif
@@ -3909,11 +3898,7 @@ __libc_calloc (size_t n, size_t elem_size)
#if USE_TCACHE
size_t nb = checked_request2size (bytes);
if (nb == 0)
{
__set_errno (ENOMEM);
return NULL;
}
if (nb < mp_.tcache_max_bytes)
{
if (__glibc_unlikely (tcache == NULL))
@@ -3988,12 +3973,12 @@ _int_malloc (mstate av, size_t bytes)
aligned.
*/
nb = checked_request2size (bytes);
if (nb == 0)
if (bytes > PTRDIFF_MAX)
{
__set_errno (ENOMEM);
return NULL;
}
nb = checked_request2size (bytes);
/* There are no usable arenas. Fall back to sysmalloc to get a chunk from
mmap. */
@@ -5148,12 +5133,12 @@ _int_memalign (mstate av, size_t alignment, size_t bytes)
unsigned long remainder_size; /* its size */
INTERNAL_SIZE_T size;
nb = checked_request2size (bytes);
if (nb == 0)
if (bytes > PTRDIFF_MAX)
{
__set_errno (ENOMEM);
return NULL;
}
nb = checked_request2size (bytes);
/* We can't check tcache here because we hold the arena lock, which
tcache doesn't expect. We expect it has been checked