Commit afd59424 authored by Edward Cree's avatar Edward Cree Committed by Alexei Starovoitov
Browse files

bpf: fix off-by-one error in adjust_subprog_starts 



When patching in a new sequence for the first insn of a subprog, the start
 of that subprog does not change (it's the first insn of the sequence), so
 adjust_subprog_starts should check start <= off (rather than < off).
Also added a test to test_verifier.c (it's essentially the syz reproducer).

Fixes: cc8b0b92 ("bpf: introduce function calls (function boundaries)")
Reported-by: default avatar <syzbot+4fc427c7af994b0948be@syzkaller.appspotmail.com>
Signed-off-by: default avatarEdward Cree <ecree@solarflare.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent da85d8bf

kernel/bpf/verifier.c

+1 −1
Original line number Diff line number Diff line
@@ -5650,7 +5650,7 @@ static void adjust_subprog_starts(struct bpf_verifier_env *env, u32 off, u32 len 
		return;

	/* NOTE: fake 'exit' subprog should be updated as well. */

	for (i = 0; i <= env->subprog_cnt; i++) {

		if (env->subprog_info[i].start < off)

		if (env->subprog_info[i].start <= off)

			continue;

		env->subprog_info[i].start += len - 1;

	}

tools/testing/selftests/bpf/test_verifier.c

+19 −0
Original line number Diff line number Diff line
@@ -13896,6 +13896,25 @@ static struct bpf_test tests[] = { 
		.prog_type = BPF_PROG_TYPE_SCHED_CLS,

		.result = ACCEPT,

	},

	{

		"calls: ctx read at start of subprog",

		.insns = {

			BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),

			BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 5),

			BPF_JMP_REG(BPF_JSGT, BPF_REG_0, BPF_REG_0, 0),

			BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),

			BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 1, 0, 2),

			BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),

			BPF_EXIT_INSN(),

			BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_1, 0),

			BPF_MOV64_IMM(BPF_REG_0, 0),

			BPF_EXIT_INSN(),

		},

		.prog_type = BPF_PROG_TYPE_SOCKET_FILTER,

		.errstr_unpriv = "function calls to other bpf functions are allowed for root only",

		.result_unpriv = REJECT,

		.result = ACCEPT,

	},

};



static int probe_filter_length(const struct bpf_insn *fp)

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