From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Baoquan He <bhe@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
Dave Young <dyoung@redhat.com>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] vmcore: replace strncpy with strtomem
Date: Thu, 28 Mar 2024 15:03:21 -0700 [thread overview]
Message-ID: <202403281502.BD156CD01@keescook> (raw)
In-Reply-To: <20240327-strncpy-fs-proc-vmcore-c-v1-1-e025ed08b1b0@google.com>
On Wed, Mar 27, 2024 at 09:10:52PM +0000, Justin Stitt wrote:
> strncpy() is in the process of being replaced as it is deprecated in
> some situations [1]. While the specific use of strncpy that this patch
> targets is not exactly deprecated, the real mission is to rid the kernel
> of all its uses.
>
> Looking at vmcoredd_header's definition:
> | struct vmcoredd_header {
> | __u32 n_namesz; /* Name size */
> | __u32 n_descsz; /* Content size */
> | __u32 n_type; /* NT_VMCOREDD */
> | __u8 name[8]; /* LINUX\0\0\0 */
> | __u8 dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Device dump's name */
> | };
> ... we can see that both `name` and `dump_name` are u8s. It seems `name`
> wants to be NUL-padded (based on the comment above), but for the sake of
> symmetry lets NUL-pad both of these.
Do we have a way to know that dump_name is not parsed by userspace as a
NUL-terminated string?
>
> Mark these buffers as __nonstring and use strtomem_pad.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
>
> Found with: $ rg "strncpy\("
> ---
> fs/proc/vmcore.c | 5 ++---
> include/uapi/linux/vmcore.h | 4 ++--
> 2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 1fb213f379a5..5d7ecf3b75e8 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -1370,9 +1370,8 @@ static void vmcoredd_write_header(void *buf, struct vmcoredd_data *data,
> vdd_hdr->n_descsz = size + sizeof(vdd_hdr->dump_name);
> vdd_hdr->n_type = NT_VMCOREDD;
>
> - strncpy((char *)vdd_hdr->name, VMCOREDD_NOTE_NAME,
> - sizeof(vdd_hdr->name));
> - memcpy(vdd_hdr->dump_name, data->dump_name, sizeof(vdd_hdr->dump_name));
> + strtomem_pad(vdd_hdr->name, VMCOREDD_NOTE_NAME, 0);
> + strtomem_pad(vdd_hdr->dump_name, data->dump_name, 0);
> }
>
> /**
> diff --git a/include/uapi/linux/vmcore.h b/include/uapi/linux/vmcore.h
> index 3e9da91866ff..7053e2b62fa0 100644
> --- a/include/uapi/linux/vmcore.h
> +++ b/include/uapi/linux/vmcore.h
> @@ -11,8 +11,8 @@ struct vmcoredd_header {
> __u32 n_namesz; /* Name size */
> __u32 n_descsz; /* Content size */
> __u32 n_type; /* NT_VMCOREDD */
> - __u8 name[8]; /* LINUX\0\0\0 */
> - __u8 dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Device dump's name */
> + __u8 name[8] __nonstring; /* LINUX\0\0\0 */
> + __u8 dump_name[VMCOREDD_MAX_NAME_BYTES] __nonstring; /* Device dump's name */
> };
Unfortunately since this is UAPI, we can't sanely use __nonstring here.
:(
--
Kees Cook
prev parent reply other threads:[~2024-03-28 22:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-27 21:10 [PATCH] vmcore: replace strncpy with strtomem Justin Stitt
2024-03-28 1:48 ` Baoquan He
2024-03-28 20:42 ` Justin Stitt
2024-03-28 22:03 ` Kees Cook [this message]
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