Re: [PATCH v2 1/7] kdb: Fix buffer overflow during tab-complete

[Daniel Thompson]

On Mon, Apr 22, 2024 at 04:51:49PM -0700, Doug Anderson wrote:
> Hi,
>
> On Mon, Apr 22, 2024 at 9:37 AM Daniel Thompson
> <daniel.thompson@xxxxxxxxxx> wrote:
> >
> > Currently, when the user attempts symbol completion with the Tab key, kdb
> > will use strncpy() to insert the completed symbol into the command buffer.
> > Unfortunately it passes the size of the source buffer rather than the
> > destination to strncpy() with predictably horrible results. Most obviously
> > if the command buffer is already full but cp, the cursor position, is in
> > the middle of the buffer, then we will write past the end of the supplied
> > buffer.
> >
> > Fix this by replacing the dubious strncpy() calls with memmove()/memcpy()
> > calls plus explicit boundary checks to make sure we have enough space
> > before we start moving characters around.
> >
> > Reported-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> > Closes: https://lore.kernel.org/all/CAFhGd8qESuuifuHsNjFPR-Va3P80bxrw+LqvC8deA8GziUJLpw@xxxxxxxxxxxxxx/
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> > ---
> >  kernel/debug/kdb/kdb_io.c | 21 +++++++++++++--------
> >  1 file changed, 13 insertions(+), 8 deletions(-)
>
> Boy, this function (and especially the tab handling) is hard to read.

Too right. I even rewrote it using offsets rather than pointers at one
point (it didn't really make it much clearer so I dropped that for now).


> I spent a bit of time trying to grok it and, as far as I can tell,
> your patch makes things better and I don't see any bugs.
>
> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

Thanks!

Daniel.