On Fri, May 29, 2020 at 1:45 PM Song Liu <songliubraving@xxxxxx> wrote:
>
>
>
> > On May 28, 2020, at 5:48 PM, Yonghong Song <yhs@xxxxxx> wrote:
> >
> > In bpf_seq_printf() helper, when user specified a "%s" in the
> > format string, strncpy_from_unsafe() is used to read the actual string
> > to a buffer. The string could be a format string or a string in
> > the kernel data structure. It is really unlikely that the string
> > will reside in the user memory.
> >
> > This is different from Commit b2a5212fb634 ("bpf: Restrict bpf_trace_printk()'s %s
> > usage and add %pks, %pus specifier") which still used
> > strncpy_from_unsafe() for "%s" to preserve the old behavior.
> >
> > If in the future, bpf_seq_printf() indeed needs to read user
> > memory, we can implement "%pus" format string.
> >
> > Based on discussion in [1], if the intent is to read kernel memory,
> > strncpy_from_unsafe_strict() should be used. So this patch
> > changed to use strncpy_from_unsafe_strict().
> >
> > [1]: https://lore.kernel.org/bpf/20200521152301.2587579-1-hch@xxxxxx/T/
> >
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Signed-off-by: Yonghong Song <yhs@xxxxxx>
>
> Acked-by: Song Liu <songliubraving@xxxxxx>
>
> I guess we should add:
>
> Fixes: 492e639f0c22 ("bpf: Add bpf_seq_printf and bpf_seq_write helpers")
Applied. Thanks
