On Tue, Sep 19, 2023 at 05:30:35AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
>
> We should favor a more robust and less ambiguous interface.
>
> We expect that both `nullb->disk_name` and `disk->disk_name` be
> NUL-terminated:
> | snprintf(nullb->disk_name, sizeof(nullb->disk_name),
> | "%s", config_item_name(&dev->group.cg_item));
> ...
> | pr_info("disk %s created\n", nullb->disk_name);
>
> It seems like NUL-padding may be required due to __assign_disk_name()
> utilizing a memcpy as opposed to a `str*cpy` api.
> | static inline void __assign_disk_name(char *name, struct gendisk *disk)
> | {
> | if (disk)
> | memcpy(name, disk->disk_name, DISK_NAME_LEN);
> | else
> | memset(name, 0, DISK_NAME_LEN);
> | }
>
> Then we go and print it with `__print_disk_name` which wraps `nullb_trace_disk_name()`.
> | #define __print_disk_name(name) nullb_trace_disk_name(p, name)
>
> This function obviously expects a NUL-terminated string.
> | const char *nullb_trace_disk_name(struct trace_seq *p, char *name)
> | {
> | const char *ret = trace_seq_buffer_ptr(p);
> |
> | if (name && *name)
> | trace_seq_printf(p, "disk=%s, ", name);
> | trace_seq_putc(p, 0);
> |
> | return ret;
> | }
>
> From the above, we need both 1) a NUL-terminated string and 2) a
> NUL-padded string. So, let's use strscpy_pad() as per Kees' suggestion
> from v1.
>
> 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@xxxxxxxxxxxxxxx
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Thanks for the analysis in the commit log, and yeah, this looks right to
me.
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
