2014-10-20 21:55:09

by Alexei Starovoitov

Subject: [PATCH net] bpf: fix bug in eBPF verifier

while comparing for verifier state equivalency the comparison
was missing a check for uninitialized register.
Make sure it does so and add a testcase.

Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
Cc: Hannes Frederic Sowa <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
---

while we were staring at the verifier code with Hannes during LPC
something felt odd in this spot. Yes. It was a bug. Fix it.

kernel/bpf/verifier.c | 3 ++-
samples/bpf/test_verifier.c | 11 +++++++++++
2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 801f5f3..9f81818 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1409,7 +1409,8 @@ static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
if (memcmp(&old->regs[i], &cur->regs[i],
sizeof(old->regs[0])) != 0) {
if (old->regs[i].type == NOT_INIT ||
- old->regs[i].type == UNKNOWN_VALUE)
+ (old->regs[i].type == UNKNOWN_VALUE &&
+ cur->regs[i].type != NOT_INIT))
continue;
return false;
}
diff --git a/samples/bpf/test_verifier.c b/samples/bpf/test_verifier.c
index f44ef11..eb4bec0 100644
--- a/samples/bpf/test_verifier.c
+++ b/samples/bpf/test_verifier.c
@@ -209,6 +209,17 @@ static struct bpf_test tests[] = {
.result = REJECT,
},
{
+ "program doesn't init R0 before exit in all branches",
+ .insns = {
+ BPF_JMP_IMM(BPF_JGE, BPF_REG_1, 0, 2),
+ BPF_MOV64_IMM(BPF_REG_0, 1),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 2),
+ BPF_EXIT_INSN(),
+ },
+ .errstr = "R0 !read_ok",
+ .result = REJECT,
+ },
+ {
"stack out of bounds",
.insns = {
BPF_ST_MEM(BPF_DW, BPF_REG_10, 8, 0),
--
1.7.9.5

2014-10-21 10:35:47

by Hannes Frederic Sowa

Subject: Re: [PATCH net] bpf: fix bug in eBPF verifier

On Mo, 2014-10-20 at 14:54 -0700, Alexei Starovoitov wrote:
> while comparing for verifier state equivalency the comparison
> was missing a check for uninitialized register.
> Make sure it does so and add a testcase.
>
> Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
> Cc: Hannes Frederic Sowa <[email protected]>
> Signed-off-by: Alexei Starovoitov <[email protected]>
> ---
>
> while we were staring at the verifier code with Hannes during LPC
> something felt odd in this spot. Yes. It was a bug. Fix it.
>
> kernel/bpf/verifier.c | 3 ++-
> samples/bpf/test_verifier.c | 11 +++++++++++
> 2 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 801f5f3..9f81818 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1409,7 +1409,8 @@ static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
> if (memcmp(&old->regs[i], &cur->regs[i],
> sizeof(old->regs[0])) != 0) {
> if (old->regs[i].type == NOT_INIT ||
> - old->regs[i].type == UNKNOWN_VALUE)
> + (old->regs[i].type == UNKNOWN_VALUE &&
> + cur->regs[i].type != NOT_INIT))
> continue;
> return false;
> }

That makes sense.

Acked-by: Hannes Frederic Sowa <[email protected]>

Thanks,
Hannes

2014-10-22 01:44:24

by David Miller

Subject: Re: [PATCH net] bpf: fix bug in eBPF verifier

From: Alexei Starovoitov <[email protected]>
Date: Mon, 20 Oct 2014 14:54:57 -0700

> while comparing for verifier state equivalency the comparison
> was missing a check for uninitialized register.
> Make sure it does so and add a testcase.
>
> Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier")
> Cc: Hannes Frederic Sowa <[email protected]>
> Signed-off-by: Alexei Starovoitov <[email protected]>

Applied, thanks.