From: Alex Dewar > Sent: 25 August 2020 09:18 > 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. > > The buffer size should probably be SYSFS_BUF_LEN not PAGE_SIZE > > (even it happens to typically be the same). > > If PAGE_SIZE is big (or small) passing a 4k buffer may be > > more appropriate than a PAGE_SIZE one. > > > > David > > We could use scnprintf() instead I guess. But an expression like: > return sprintf(buf, "%d\n", value); > will never overflow if buf is PAGE_SIZE, right...? Certainly the return value from snprintf() isn't what you want here (it almost never is) - so scnprintf() is much better. A simple "%d" or "%u" wont overflow, but a "%s" might (even if it is really expected that it shouldn't). Even a "%*d" can go horribly wrong. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
