linux-kernel - Re: [RFC PATCH v1 1/2] maccess: fix writing offset in case of fault in strncpy_from_kernel

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Date:   Tue, 8 Nov 2022 13:05:51 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Francis Laniel <flaniel@...ux.microsoft.com>
Cc:     linux-kernel@...r.kernel.org,
        Alban Crequy <alban.crequy@...il.com>,
        Alban Crequy <albancrequy@...rosoft.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>, linux-mm@...ck.org,
        bpf@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/2] maccess: fix writing offset in case of fault
 in strncpy_from_kernel_nofault()

On Tue,  8 Nov 2022 20:52:06 +0100 Francis Laniel <flaniel@...ux.microsoft.com> wrote:

> From: Alban Crequy <albancrequy@...rosoft.com>
> 
> If a page fault occurs while copying the first byte, this function resets one
> byte before dst.
> As a consequence, an address could be modified and leaded to kernel crashes if
> case the modified address was accessed later.
> 
> Signed-off-by: Alban Crequy <albancrequy@...rosoft.com>
> Tested-by: Francis Laniel <flaniel@...ux.microsoft.com>

Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>

Please merge via the bpf tree.

This looks potentially nasty.  Fortunately only tracing code uses it,
but I'm thinking it should have cc:stable and a Fixes:?