On Tue, Jan 15, 2019 at 12:47:34PM -0800, Kees Cook wrote: > On Sat, Jan 12, 2019 at 7:28 AM Willy Tarreau <w...@1wt.eu> wrote: > > > > From: Silvio Cesare <silvio.ces...@gmail.com> > > > > Change snprintf to scnprintf. There are generally two cases where using > > snprintf causes problems. > > > > 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...) > > In this case, if snprintf would have written more characters than what the > > buffer size (SIZE) is, then size will end up larger than SIZE. In later > > uses of snprintf, SIZE - size will result in a negative number, leading > > to problems. Note that size might already be too large by using > > size = snprintf before the code reaches a case of size += snprintf. > > > > 2) If size is ultimately used as a length parameter for a copy back to user > > space, then it will potentially allow for a buffer overflow and information > > disclosure when size is greater than SIZE. When the size is used to index > > the buffer directly, we can have memory corruption. This also means when > > size = snprintf... is used, it may also cause problems since size may become > > large. Copying to userspace is mitigated by the HARDENED_USERCOPY kernel > > configuration. > > > > The solution to these issues is to use scnprintf which returns the number of > > characters actually written to the buffer, so the size variable will never > > exceed SIZE. > > > > Signed-off-by: Silvio Cesare <silvio.ces...@gmail.com> > > Cc: Dan Carpenter <dan.carpen...@oracle.com> > > Cc: Kees Cook <keesc...@chromium.org> > > Cc: Will Deacon <will.dea...@arm.com> > > Cc: Greg KH <g...@kroah.com> > > Signed-off-by: Willy Tarreau <w...@1wt.eu> > > It looks like these are going via individual trees. Greg, can you > please take this into your drivers-misc tree for lkdtm? > > Acked-by: Kees Cook <keesc...@chromium.org>
Will do, thanks. greg k-h
