On Thu, Aug 26, 2021 at 1:12 AM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> From: Peter Collingbourne
> > Sent: 26 August 2021 02:27
> >
> > A common implementation of isatty(3) involves calling a ioctl passing
> > a dummy struct argument and checking whether the syscall failed --
> > bionic and glibc use TCGETS (passing a struct termios), and musl uses
> > TIOCGWINSZ (passing a struct winsize). If the FD is a socket, we will
> > copy sizeof(struct ifreq) bytes of data from the argument and return
> > -EFAULT if that fails. The result is that the isatty implementations
> > may return a non-POSIX-compliant value in errno in the case where part
> > of the dummy struct argument is inaccessible, as both struct termios
> > and struct winsize are smaller than struct ifreq (at least on arm64).
> >
> > Although there is usually enough stack space following the argument
> > on the stack that this did not present a practical problem up to now,
> > with MTE stack instrumentation it's more likely for the copy to fail,
> > as the memory following the struct may have a different tag.
> >
> > Fix the problem by adding an early check for whether the ioctl is a
> > valid socket ioctl, and return -ENOTTY if it isn't.
> ..
> > +bool is_dev_ioctl_cmd(unsigned int cmd)
> > +{
> > + switch (cmd) {
> > + case SIOCGIFNAME:
> > + case SIOCGIFHWADDR:
> > + case SIOCGIFFLAGS:
> > + case SIOCGIFMETRIC:
> > + case SIOCGIFMTU:
> > + case SIOCGIFSLAVE:
> > + case SIOCGIFMAP:
> > + case SIOCGIFINDEX:
> > + case SIOCGIFTXQLEN:
> > + case SIOCETHTOOL:
> > + case SIOCGMIIPHY:
> > + case SIOCGMIIREG:
> > + case SIOCSIFNAME:
> > + case SIOCSIFMAP:
> > + case SIOCSIFTXQLEN:
> > + case SIOCSIFFLAGS:
> > + case SIOCSIFMETRIC:
> > + case SIOCSIFMTU:
> > + case SIOCSIFHWADDR:
> > + case SIOCSIFSLAVE:
> > + case SIOCADDMULTI:
> > + case SIOCDELMULTI:
> > + case SIOCSIFHWBROADCAST:
> > + case SIOCSMIIREG:
> > + case SIOCBONDENSLAVE:
> > + case SIOCBONDRELEASE:
> > + case SIOCBONDSETHWADDR:
> > + case SIOCBONDCHANGEACTIVE:
> > + case SIOCBRADDIF:
> > + case SIOCBRDELIF:
> > + case SIOCSHWTSTAMP:
> > + case SIOCBONDSLAVEINFOQUERY:
> > + case SIOCBONDINFOQUERY:
> > + case SIOCGIFMEM:
> > + case SIOCSIFMEM:
> > + case SIOCSIFLINK:
> > + case SIOCWANDEV:
> > + case SIOCGHWTSTAMP:
> > + return true;
>
> That is horrid.
> Can't you at least use _IOC_TYPE() to check for socket ioctls.
> Clearly it can succeed for 'random' driver ioctls, but will fail
> for the tty ones.
Yes, that works, since all of the ioctls listed above are in the range
where the _IOC_TYPE() check would succeed. It now also makes sense to
move the check inline into the header. I've done all of that in v2.
> The other sane thing is to check _IOC_SIZE().
> Since all the SIOCxxxx have a correct _IOC_SIZE() that can be
> used to check the user copy length.
> (Unlike socket options the correct length is always supplied.
FWIW, it doesn't look like any of them have the _IOC_SIZE() bits set,
so that won't work. _IOC_TYPE() seems better anyway.
Peter
