linux-kernel - Re: [PATCH] arm64: bpf: fix out-of-bounds read in bpf2a64

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Message-ID: <558C0354.4080809@plumgrid.com>
Date:	Thu, 25 Jun 2015 06:34:12 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Xi Wang <xi.wang@...il.com>, linux-arm-kernel@...ts.infradead.org
CC:	linux-kernel@...r.kernel.org, Zi Shen Lim <zlim.lnx@...il.com>,
	Will Deacon <will.deacon@....com>
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<zlim.lnx@...il.com>
> Cc: Alexei Starovoitov<ast@...mgrid.com>
> Cc: Will Deacon<will.deacon@....com>
> Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
> Signed-off-by: Xi Wang<xi.wang@...il.com>

Nice catch! Looks good to me.
Acked-by: Alexei Starovoitov <ast@...mgrid.com>

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