On Mon, Jan 21, 2019 at 01:20:57PM +0100, Miklos Szeredi wrote:
> On Tue, Nov 20, 2018 at 6:36 AM Chandan Rajendra
> <chandan@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > On ppc64le, When a string with PAGE_SIZE - 1 (i.e. 64k-1) length is
> > passed as a "filesystem type" argument to the mount(2) syscall,
> > copy_mount_string() ends up allocating 64k (the PAGE_SIZE on ppc64le)
> > worth of space for holding the string in kernel's address space.
> >
> > Later, in set_precision() (invoked by get_fs_type() ->
> > __request_module() -> vsnprintf()), we end up assigning
> > strlen(fs-type-string) i.e. 65535 as the
> > value to 'struct printf_spec'->precision member. This field has a width
> > of 16 bits and it is a signed data type. Hence an invalid value ends
> > up getting assigned. This causes the "WARN_ONCE(spec->precision != prec,
> > "precision %d too large", prec)" statement inside set_precision() to be
> > executed.
> >
> > This commit fixes the bug by validating the length of the "filesystem
> > type" argument passed to get_fs_type() function.
> >
> > Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx>
> > Reported-by: Abdul Haleem <abdhalee@xxxxxxxxxxxxxxxxxx>
> > Suggested-by: Joe Perches <joe@xxxxxxxxxxx>
>
> Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
>
> Al, please pick this up, it looks like a good sanity check and lack of
> it is causing headaches for IBM QA.
Umm... I'm not against that patch, but I wonder if that should be caught
earlier... If nothing else, the same string is seen by LSM shite before
get_fs_type() gets a chance to reject it, and I wouldn't bet a dime on
robustness of that code. Wouldn't it be saner to have
char *copy_mount_string(const void __user *data)
{
return data ? strndup_user(data, PAGE_SIZE) : NULL;
}
use a more explicit size limit? PATH_MAX, for example?
