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Commit 9305706c authored by Edward Cree's avatar Edward Cree Committed by David S. Miller
Browse files

bpf/verifier: fix min/max handling in BPF_SUB 



We have to subtract the src max from the dst min, and vice-versa, since
 (e.g.) the smallest result comes from the largest subtrahend.

Fixes: 48461135 ("bpf: allow access into map value arrays")
Signed-off-by: default avatarEdward Cree <ecree@solarflare.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 545722cb

kernel/bpf/verifier.c

+15 −6
Original line number Diff line number Diff line
@@ -1865,10 +1865,12 @@ static void adjust_reg_min_max_vals(struct bpf_verifier_env *env, 
	 * do our normal operations to the register, we need to set the values

	 * to the min/max since they are undefined.

	 */

	if (opcode != BPF_SUB) {

		if (min_val == BPF_REGISTER_MIN_RANGE)

			dst_reg->min_value = BPF_REGISTER_MIN_RANGE;

		if (max_val == BPF_REGISTER_MAX_RANGE)

			dst_reg->max_value = BPF_REGISTER_MAX_RANGE;

	}



	switch (opcode) {

	case BPF_ADD:
@@ -1879,10 +1881,17 @@ static void adjust_reg_min_max_vals(struct bpf_verifier_env *env, 
		dst_reg->min_align = min(src_align, dst_align);

		break;

	case BPF_SUB:

		/* If one of our values was at the end of our ranges, then the

		 * _opposite_ value in the dst_reg goes to the end of our range.

		 */

		if (min_val == BPF_REGISTER_MIN_RANGE)

			dst_reg->max_value = BPF_REGISTER_MAX_RANGE;

		if (max_val == BPF_REGISTER_MAX_RANGE)

			dst_reg->min_value = BPF_REGISTER_MIN_RANGE;

		if (dst_reg->min_value != BPF_REGISTER_MIN_RANGE)

			dst_reg->min_value -= min_val;

			dst_reg->min_value -= max_val;

		if (dst_reg->max_value != BPF_REGISTER_MAX_RANGE)

			dst_reg->max_value -= max_val;

			dst_reg->max_value -= min_val;

		dst_reg->min_align = min(src_align, dst_align);

		break;

	case BPF_MUL: