On 03/27/24 at 09:10pm, 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.
>
> Mark these buffers as __nonstring and use strtomem_pad.
Thanks.
I didn't build, wondering if '__nonstring' has to be set so that
strtomem_pad() can be used.
Thanks
Baoquan
>
> 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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
> ---
> 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 */
> };
>
> #endif /* _UAPI_VMCORE_H */
>
> ---
> base-commit: 928a87efa42302a23bb9554be081a28058495f22
> change-id: 20240327-strncpy-fs-proc-vmcore-c-b18d761feaef
>
> Best regards,
> --
> Justin Stitt <[email protected]>
>
Hi,
On Wed, Mar 27, 2024 at 6:48 PM Baoquan He <[email protected]> wrote:
> > Mark these buffers as __nonstring and use strtomem_pad.
>
> Thanks.
>
> I didn't build, wondering if '__nonstring' has to be set so that
> strtomem_pad() can be used.
I do not believe marking buffers as __nonstring is strictly a
requirement. However, the documentation from string.h +302 says we
should do it:
/**
* strtomem_pad - Copy NUL-terminated string to non-NUL-terminated buffer
*
* @dest: Pointer of destination character array (marked as __nonstring)
..
and so does [1] ... "mark the destination buffer variable (or
structure member) with the __nonstring attribute..."
FWIW, this builds just fine without the __nonstring attribute but we
should use it :)
>
> Thanks
> Baoquan
>
[1] https://github.com/KSPP/linux/issues/90
Thanks
Justin