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. > 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. -Kees [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=11990a5bd7e558e9203c1070fc52fb6f0488e75b -- Kees Cook
