fuse: Add ioctl flag for x32 compat ioctl

Currently, a CUSE server running on a 64-bit kernel can tell when an ioctl
request comes from a process running a 32-bit ABI, but cannot tell whether
the requesting process is using legacy IA32 emulation or x32 ABI.  In
particular, the server does not know the size of the client process's
`time_t` type.

For 64-bit kernels, the `FUSE_IOCTL_COMPAT` and `FUSE_IOCTL_32BIT` flags
are currently set in the ioctl input request (`struct fuse_ioctl_in` member
`flags`) for a 32-bit requesting process.  This patch defines a new flag
`FUSE_IOCTL_COMPAT_X32` and sets it if the 32-bit requesting process is
using the x32 ABI.  This allows the server process to distinguish between
requests coming from client processes using IA32 emulation or the x32 ABI
and so infer the size of the client process's `time_t` type and any other
IA32/x32 differences.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -2578,8 +2578,13 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 #if BITS_PER_LONG == 32
 	inarg.flags |= FUSE_IOCTL_32BIT;
 #else
-	if (flags & FUSE_IOCTL_COMPAT)
+	if (flags & FUSE_IOCTL_COMPAT) {
 		inarg.flags |= FUSE_IOCTL_32BIT;
+#ifdef CONFIG_X86_X32
+		if (in_x32_syscall())
+			inarg.flags |= FUSE_IOCTL_COMPAT_X32;
+#endif
+	}
 #endif
 
 	/* assume all the iovs returned by client always fits in a page */

include/uapi/linux/fuse.h

@@ -129,6 +129,7 @@
  *
  *  7.30
  *  - add FUSE_EXPLICIT_INVAL_DATA
+ *  - add FUSE_IOCTL_COMPAT_X32
  */
 
 #ifndef _LINUX_FUSE_H
@@ -343,6 +344,7 @@ struct fuse_file_lock {
  * FUSE_IOCTL_RETRY: retry with new iovecs
  * FUSE_IOCTL_32BIT: 32bit ioctl
  * FUSE_IOCTL_DIR: is a directory
+ * FUSE_IOCTL_COMPAT_X32: x32 compat ioctl on 64bit machine (64bit time_t)
  *
  * FUSE_IOCTL_MAX_IOV: maximum of in_iovecs + out_iovecs
  */
@@ -351,6 +353,7 @@ struct fuse_file_lock {
 #define FUSE_IOCTL_RETRY	(1 << 2)
 #define FUSE_IOCTL_32BIT	(1 << 3)
 #define FUSE_IOCTL_DIR		(1 << 4)
+#define FUSE_IOCTL_COMPAT_X32	(1 << 5)
 
 #define FUSE_IOCTL_MAX_IOV	256