On Thu, Apr 25, 2019 at 5:35 PM Al Viro viro@zeniv.linux.org.uk wrote:
On Thu, Apr 25, 2019 at 12:21:53PM -0300, Mauro Carvalho Chehab wrote:
If I understand your patch description well, using compat_ptr_ioctl only works if the driver is not for s390, right?
No; s390 is where "oh, just set ->compat_ioctl same as ->unlocked_ioctl and be done with that; compat_ptr() is a no-op anyway" breaks. IOW, s390 is the reason for having compat_ptr_ioctl() in the first place; that thing works on all biarch architectures, as long as all stuff handled by ->ioctl() takes pointer to arch-independent object as argument. IOW, argument ignored => OK any arithmetical type => no go, compat_ptr() would bugger it pointer to int => OK pointer to string => OK pointer to u64 => OK pointer to struct {u64 addr; char s[11];} => OK
To be extra pedantic, the 'struct {u64 addr; char s[11];} ' case is also broken on x86, because sizeof (obj) is smaller on i386, even though the location of the members are the same. i.e. you can copy_from_user() this, but not copy_to_user(), which overwrites 4 bytes after the end of the 20-byte user structure.
Arnd