Re: [PATCH v2 1/7] scripts: modpost: detect and report truncated buf_printf() output

[Nathan Chancellor]

On Thu, May 28, 2026 at 10:23:18PM +0900, Alexandre Courbot wrote:
> Hi Nathan,
> 
> On Thu May 28, 2026 at 2:18 AM JST, Nathan Chancellor wrote:
> > On Wed, May 27, 2026 at 08:52:17PM +0900, Alexandre Courbot wrote:
> >> buf_printf() uses a fixed-size stack buffer. vsnprintf() returns the
> >> number of bytes that *would* have been written to that buffer, which can
> >> be larger than the size of said buffer if the formatted string is too
> >> long.
> >> 
> >> The problem is that whenever this happens buf_printf() currently passes
> >> this length, unchecked, to buf_write(), which silently reads past the
> >> stack buffer and copies invalid data into the output buffer.
> >> 
> >> Fix this by detecting vsnprintf() failures and truncations before
> >> appending to the output buffer, and report a fatal error instead of
> >> producing corrupt symbol names.
> >> 
> >> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
> >
> > Acked-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> 
> If that works for you, can you take this patch through the build tree?
> I've included it in this series because it detects the issue that the
> series fixes, but it is not a dependency for the next patches. I just
> wanted to include it for context.

Sure, I can pick this one up through the Kbuild tree.

-- 
Cheers,
Nathan