[PATCH v2 11/16] bpf: Use kmalloc_size_roundup() to match ksize() usage

Kees Cook
2022-09-23T20:34:59Z

Round up allocations with kmalloc_size_roundup() so that the verifier's
use of ksize() is always accurate and no special handling of the memory
is needed by KASAN, UBSAN_BOUNDS, nor FORTIFY_SOURCE. Pass the new size
information back up to callers so they can use the space immediately,
so array resizing to happen less frequently as well. Explicitly zero
any trailing bytes in new allocations.

Additionally fix a memory allocation leak: if krealloc() fails, "arr"
wasn't freed, but NULL was return to the caller of realloc_array() would
be writing NULL to the lvalue, losing the reference to the original
memory.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: bpf@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
kernel/bpf/verifier.c | 49 +++++++++++++++++++++++++++----------------
1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 096fdac70165..80531f8f0d36 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -978,42 +978,53 @@ static void print_insn_state(struct bpf_verifier_env *env,
*/
static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t flags)
{
- size_t bytes;
+ size_t src_bytes, dst_bytes;

if (ZERO_OR_NULL_PTR(src))
goto out;

- if (unlikely(check_mul_overflow(n, size, &bytes)))
+ if (unlikely(check_mul_overflow(n, size, &src_bytes)))
return NULL;

- if (ksize(dst) < bytes) {
+ dst_bytes = kmalloc_size_roundup(src_bytes);
+ if (ksize(dst) < dst_bytes) {
kfree(dst);
- dst = kmalloc_track_caller(bytes, flags);
+ dst = kmalloc_track_caller(dst_bytes, flags);
if (!dst)
return NULL;
}

- memcpy(dst, src, bytes);
+ memcpy(dst, src, src_bytes);
+ memset(dst + src_bytes, 0, dst_bytes - src_bytes);
out:
return dst ? dst : ZERO_SIZE_PTR;
}

-/* resize an array from old_n items to new_n items. the array is reallocated if it's too
- * small to hold new_n items. new items are zeroed out if the array grows.
+/* Resize an array from old_n items to *new_n items. The array is reallocated if it's too
+ * small to hold *new_n items. New items are zeroed out if the array grows. Allocation
+ * is rounded up to next kmalloc bucket size to reduce frequency of resizing. *new_n
+ * contains the new total number of items that will fit.
*
- * Contrary to krealloc_array, does not free arr if new_n is zero.
+ * Contrary to krealloc, does not free arr if new_n is zero.
*/
-static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
+static void *realloc_array(void *arr, size_t old_n, size_t *new_n, size_t size)
{
- if (!new_n || old_n == new_n)
+ void *old_arr = arr;
+ size_t alloc_size;
+
+ if (!new_n || !*new_n || old_n == *new_n)
goto out;

- arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
- if (!arr)
+ alloc_size = kmalloc_size_roundup(size_mul(*new_n, size));
+ arr = krealloc(old_arr, alloc_size, GFP_KERNEL);
+ if (!arr) {
+ kfree(old_arr);
return NULL;
+ }

- if (new_n > old_n)
- memset(arr + old_n * size, 0, (new_n - old_n) * size);
+ *new_n = alloc_size / size;
+ if (*new_n > old_n)
+ memset(arr + old_n * size, 0, (*new_n - old_n) * size);

out:
return arr ? arr : ZERO_SIZE_PTR;
@@ -1045,7 +1056,7 @@ static int copy_stack_state(struct bpf_func_state *dst, const struct bpf_func_st

static int resize_reference_state(struct bpf_func_state *state, size_t n)
{
- state->refs = realloc_array(state->refs, state->acquired_refs, n,
+ state->refs = realloc_array(state->refs, state->acquired_refs, &n,
sizeof(struct bpf_reference_state));
if (!state->refs)
return -ENOMEM;
@@ -1061,11 +1072,11 @@ static int grow_stack_state(struct bpf_func_state *state, int size)
if (old_n >= n)
return 0;

- state->stack = realloc_array(state->stack, old_n, n, sizeof(struct bpf_stack_state));
+ state->stack = realloc_array(state->stack, old_n, &n, sizeof(struct bpf_stack_state));
if (!state->stack)
return -ENOMEM;

- state->allocated_stack = size;
+ state->allocated_stack = n * BPF_REG_SIZE;
return 0;
}

@@ -2472,9 +2483,11 @@ static int push_jmp_history(struct bpf_verifier_env *env,
{
u32 cnt = cur->jmp_history_cnt;
struct bpf_idx_pair *p;
+ size_t size;

cnt++;
- p = krealloc(cur->jmp_history, cnt * sizeof(*p), GFP_USER);
+ size = kmalloc_size_roundup(size_mul(cnt, sizeof(*p)));
+ p = krealloc(cur->jmp_history, size, GFP_USER);
if (!p)
return -ENOMEM;
p[cnt - 1].idx = env->insn_idx;
--
2.34.1