Commit 0fd4759c authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

bpf: fix pattern matches for direct packet access 



Alexander had a test program with direct packet access, where
the access test was in the form of data + X > data_end. In an
unrelated change to the program LLVM decided to swap the branches
and emitted code for the test in form of data + X <= data_end.
We hadn't seen these being generated previously, thus verifier
would reject the program. Therefore, fix up the verifier to
detect all test cases, so we don't run into such issues in the
future.

Fixes: b4e432f1 ("bpf: enable BPF_J{LT, LE, SLT, SLE} opcodes in verifier")
Reported-by: default avatarAlexander Alemayhu <alexander@alemayhu.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fb2a311a

kernel/bpf/verifier.c

+24 −0
Original line number Diff line number Diff line
@@ -2874,18 +2874,42 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, 
	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&

		   dst_reg->type == PTR_TO_PACKET &&

		   regs[insn->src_reg].type == PTR_TO_PACKET_END) {

		/* pkt_data' > pkt_end */

		find_good_pkt_pointers(this_branch, dst_reg, false);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&

		   dst_reg->type == PTR_TO_PACKET_END &&

		   regs[insn->src_reg].type == PTR_TO_PACKET) {

		/* pkt_end > pkt_data' */

		find_good_pkt_pointers(other_branch, &regs[insn->src_reg], true);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLT &&

		   dst_reg->type == PTR_TO_PACKET &&

		   regs[insn->src_reg].type == PTR_TO_PACKET_END) {

		/* pkt_data' < pkt_end */

		find_good_pkt_pointers(other_branch, dst_reg, true);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLT &&

		   dst_reg->type == PTR_TO_PACKET_END &&

		   regs[insn->src_reg].type == PTR_TO_PACKET) {

		/* pkt_end < pkt_data' */

		find_good_pkt_pointers(this_branch, &regs[insn->src_reg], false);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGE &&

		   dst_reg->type == PTR_TO_PACKET &&

		   regs[insn->src_reg].type == PTR_TO_PACKET_END) {

		/* pkt_data' >= pkt_end */

		find_good_pkt_pointers(this_branch, dst_reg, true);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGE &&

		   dst_reg->type == PTR_TO_PACKET_END &&

		   regs[insn->src_reg].type == PTR_TO_PACKET) {

		/* pkt_end >= pkt_data' */

		find_good_pkt_pointers(other_branch, &regs[insn->src_reg], false);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLE &&

		   dst_reg->type == PTR_TO_PACKET &&

		   regs[insn->src_reg].type == PTR_TO_PACKET_END) {

		/* pkt_data' <= pkt_end */

		find_good_pkt_pointers(other_branch, dst_reg, false);

	} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JLE &&

		   dst_reg->type == PTR_TO_PACKET_END &&

		   regs[insn->src_reg].type == PTR_TO_PACKET) {

		/* pkt_end <= pkt_data' */

		find_good_pkt_pointers(this_branch, &regs[insn->src_reg], true);

	} else if (is_pointer_value(env, insn->dst_reg)) {

		verbose("R%d pointer comparison prohibited\n", insn->dst_reg);

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