2015-06-25 12:48:11

by Xi Wang

Subject: [PATCH] arm64: bpf: fix out-of-bounds read in bpf2a64_offset()

Problems occur when bpf_to or bpf_from has value prog->len - 1 (e.g.,
"Very long jump backwards" in test_bpf where the last instruction is a
jump): since ctx->offset has length prog->len, ctx->offset[bpf_to + 1]
or ctx->offset[bpf_from + 1] will cause an out-of-bounds read, leading
to a bogus jump offset and kernel panic.

This patch moves updating ctx->offset to after calling build_insn(),
and changes indexing to use bpf_to and bpf_from without + 1.

Cc: Zi Shen Lim <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Will Deacon <[email protected]>
Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
Signed-off-by: Xi Wang <[email protected]>
---
arch/arm64/net/bpf_jit_comp.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index dc6a484..c81ddd4 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -113,9 +113,9 @@ static inline void emit_a64_mov_i(const int is64, const int reg,
static inline int bpf2a64_offset(int bpf_to, int bpf_from,
const struct jit_ctx *ctx)
{
- int to = ctx->offset[bpf_to + 1];
+ int to = ctx->offset[bpf_to];
/* -1 to account for the Branch instruction */
- int from = ctx->offset[bpf_from + 1] - 1;
+ int from = ctx->offset[bpf_from] - 1;

return to - from;
}
@@ -640,10 +640,11 @@ static int build_body(struct jit_ctx *ctx)
const struct bpf_insn *insn = &prog->insnsi[i];
int ret;

+ ret = build_insn(insn, ctx);
+
if (ctx->image == NULL)
ctx->offset[i] = ctx->idx;

- ret = build_insn(insn, ctx);
if (ret > 0) {
i++;
continue;
--
2.1.4

2015-06-25 13:34:23

by Alexei Starovoitov

Subject: Re: [PATCH] arm64: bpf: fix out-of-bounds read in bpf2a64_offset()

On 6/25/15 5:47 AM, Xi Wang wrote:
> Problems occur when bpf_to or bpf_from has value prog->len - 1 (e.g.,
> "Very long jump backwards" in test_bpf where the last instruction is a
> jump): since ctx->offset has length prog->len, ctx->offset[bpf_to + 1]
> or ctx->offset[bpf_from + 1] will cause an out-of-bounds read, leading
> to a bogus jump offset and kernel panic.
>
> This patch moves updating ctx->offset to after calling build_insn(),
> and changes indexing to use bpf_to and bpf_from without + 1.
>
> Cc: Zi Shen Lim<[email protected]>
> Cc: Alexei Starovoitov<[email protected]>
> Cc: Will Deacon<[email protected]>
> Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
> Signed-off-by: Xi Wang<[email protected]>

Nice catch! Looks good to me.
Acked-by: Alexei Starovoitov <[email protected]>

2015-06-25 14:26:41

by Catalin Marinas

Subject: Re: [PATCH] arm64: bpf: fix out-of-bounds read in bpf2a64_offset()

On Thu, Jun 25, 2015 at 05:47:39AM -0700, Xi Wang wrote:
> Problems occur when bpf_to or bpf_from has value prog->len - 1 (e.g.,
> "Very long jump backwards" in test_bpf where the last instruction is a
> jump): since ctx->offset has length prog->len, ctx->offset[bpf_to + 1]
> or ctx->offset[bpf_from + 1] will cause an out-of-bounds read, leading
> to a bogus jump offset and kernel panic.
>
> This patch moves updating ctx->offset to after calling build_insn(),
> and changes indexing to use bpf_to and bpf_from without + 1.
>
> Cc: Zi Shen Lim <[email protected]>
> Cc: Alexei Starovoitov <[email protected]>
> Cc: Will Deacon <[email protected]>
> Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
> Signed-off-by: Xi Wang <[email protected]>

Thanks. Applied.

--
Catalin