From: Kees Cook keescook@chromium.org
[ Upstream commit ceb35b666d42c2e91b1f94aeca95bb5eb0943268 ]
Most allocation sites in the kernel want an explicitly sized allocation (and not "more"), and that dynamic runtime analysis tools (e.g. KASAN, UBSAN_BOUNDS, FORTIFY_SOURCE, etc) are looking for precise bounds checking (i.e. not something that is rounded up). A tiny handful of allocations were doing an implicit alloc/realloc loop that actually depended on ksize(), and didn't actually always call realloc. This has created a long series of bugs and problems over many years related to the runtime bounds checking, so these callers are finally being adjusted to _not_ depend on the ksize() side-effect, by doing one of several things:
- tracking the allocation size precisely and just never calling ksize() at all [1].
- always calling realloc and not using ksize() at all. (This solution ends up actually be a subset of the next solution.)
- using kmalloc_size_roundup() to explicitly round up the desired allocation size immediately [2].
The bpf/verifier case is this another of this latter case, and is the last outstanding case to be fixed in the kernel.
Because some of the dynamic bounds checking depends on the size being an _argument_ to an allocator function (i.e. see the __alloc_size attribute), the ksize() users are rare, and it could waste local variables, it was been deemed better to explicitly separate the rounding up from the allocation itself [3].
Round up allocations with kmalloc_size_roundup() so that the verifier's use of ksize() is always accurate.
[1] e.g.: https://git.kernel.org/linus/712f210a457d https://git.kernel.org/linus/72c08d9f4c72
[2] e.g.: https://git.kernel.org/netdev/net-next/c/12d6c1d3a2ad https://git.kernel.org/netdev/net-next/c/ab3f7828c979 https://git.kernel.org/netdev/net-next/c/d6dd508080a3
[3] https://lore.kernel.org/lkml/0ea1fc165a6c6117f982f4f135093e69cb884930.camel@...
Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Stanislav Fomichev sdf@google.com Link: https://lore.kernel.org/bpf/20221118183409.give.387-kees@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 264b3dc714cc..22b2f1f74cdc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1008,9 +1008,9 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t if (unlikely(check_mul_overflow(n, size, &bytes))) return NULL;
- if (ksize(dst) < bytes) { + if (ksize(dst) < ksize(src)) { kfree(dst); - dst = kmalloc_track_caller(bytes, flags); + dst = kmalloc_track_caller(kmalloc_size_roundup(bytes), flags); if (!dst) return NULL; } @@ -1027,12 +1027,14 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t */ static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size) { + size_t alloc_size; void *new_arr;
if (!new_n || old_n == new_n) goto out;
- new_arr = krealloc_array(arr, new_n, size, GFP_KERNEL); + alloc_size = kmalloc_size_roundup(size_mul(new_n, size)); + new_arr = krealloc(arr, alloc_size, GFP_KERNEL); if (!new_arr) { kfree(arr); return NULL; @@ -2504,9 +2506,11 @@ static int push_jmp_history(struct bpf_verifier_env *env, { u32 cnt = cur->jmp_history_cnt; struct bpf_idx_pair *p; + size_t alloc_size;
cnt++; - p = krealloc(cur->jmp_history, cnt * sizeof(*p), GFP_USER); + alloc_size = kmalloc_size_roundup(size_mul(cnt, sizeof(*p))); + p = krealloc(cur->jmp_history, alloc_size, GFP_USER); if (!p) return -ENOMEM; p[cnt - 1].idx = env->insn_idx;