mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-08-21 19:05:37 -04:00
e4c8b46b92
As done for kmalloc_obj*(), introduce a type-aware allocator for flexible arrays, which may also have "counted_by" annotations: ptr = kmalloc(struct_size(ptr, flex_member, count), gfp); becomes: ptr = kmalloc_flex(*ptr, flex_member, count, gfp); The internal use of __flex_counter() allows for automatically setting the counter member of a struct's flexible array member when it has been annotated with __counted_by(), avoiding any missed early size initializations while __counted_by() annotations are added to the kernel. Additionally, this also checks for "too large" allocations based on the type size of the counter variable. For example: if (count > type_max(ptr->flex_counter)) fail...; size = struct_size(ptr, flex_member, count); ptr = kmalloc(size, gfp); if (!ptr) fail...; ptr->flex_counter = count; becomes (n.b. unchanged from earlier example): ptr = kmalloc_flex(*ptr, flex_member, count, gfp); if (!ptr) fail...; ptr->flex_counter = count; Note that manual initialization of the flexible array counter is still required (at some point) after allocation as not all compiler versions support the __counted_by annotation yet. But doing it internally makes sure they cannot be missed when __counted_by _is_ available, meaning that the bounds checker will not trip due to the lack of "early enough" initializations that used to work before enabling the stricter bounds checking. For example: ptr = kmalloc_flex(*ptr, flex_member, count, gfp); fill(ptr->flex, count); ptr->flex_count = count; This works correctly before adding a __counted_by annotation (since nothing is checking ptr->flex accesses against ptr->flex_count). After adding the annotation, the bounds sanitizer would trip during fill() because ptr->flex_count wasn't set yet. But with kmalloc_flex() setting ptr->flex_count internally at allocation time, the existing code works without needing to move the ptr->flex_count assignment before the call to fill(). (This has been a stumbling block for __counted_by adoption.) Link: https://patch.msgid.link/20251203233036.3212363-4-kees@kernel.org Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Kees Cook <kees@kernel.org>