On Thu, Aug 27, 2020 at 09:49:04AM -0700, Kees Cook wrote: > On Tue, Aug 25, 2020 at 10:24:06AM +0200, Greg Kroah-Hartman wrote: > > On Tue, Aug 25, 2020 at 08:12:05AM +0000, David Laight wrote: > > > From: Alex Dewar > > > > Sent: 24 August 2020 23:23 > > > > kernel/cpu.c: don't use snprintf() for sysfs attrs > > > > > > > > As per the documentation (Documentation/filesystems/sysfs.rst), > > > > snprintf() should not be used for formatting values returned by sysfs. > > > > > > > > In all of these cases, sprintf() suffices as we know that the formatted > > > > strings will be less than PAGE_SIZE in length. > > > > > > Hmmmm.... > > > I much prefer to see bounded string ops. > > > sysfs really ought to be passing through the buffer length. > > > > No. > > It really should, though. I _just_ got burned by this due to having > a binattr sysfs reachable through splice[1]. Most sysfs things aren't > binattr, but I've always considered this to be a weird fragility in the > sysfs implementation. binattr attributes do have the buffer size passed to it, for that very reason :) > > So this is designed this way on purpose, you shouldn't have to worry > > about any of this, and that way, you don't have to "program > > defensively", it all just works in a simple manner. > > Later in this thread there's a suggestion to alter the API to avoid > individual calls to sprintf(), which seems like a reasonable first step. I always review any patches submitted, so if someone feels like tackling this, wonderful! thanks, greg k-h
