Commit 2952db0f authored by Arnd Bergmann's avatar Arnd Bergmann
Browse files

compat_ioctl: add compat_ptr_ioctl() 



Many drivers have ioctl() handlers that are completely compatible between
32-bit and 64-bit architectures, except for the argument that is passed
down from user space and may have to be passed through compat_ptr()
in order to become a valid 64-bit pointer.

Using ".compat_ptr = compat_ptr_ioctl" in file operations should let
us simplify a lot of those drivers to avoid #ifdef checks, and convert
additional drivers that don't have proper compat handling yet.

On most architectures, the compat_ptr_ioctl() just passes all arguments
to the corresponding ->ioctl handler. The exception is arch/s390, where
compat_ptr() clears the top bit of a 32-bit pointer value, so user space
pointers to the second 2GB alias the first 2GB, as is the case for native
32-bit s390 user space.

The compat_ptr_ioctl() function must therefore be used only with
ioctl functions that either ignore the argument or pass a pointer to a
compatible data type.

If any ioctl command handled by fops->unlocked_ioctl passes a plain
integer instead of a pointer, or any of the passed data types is
incompatible between 32-bit and 64-bit architectures, a proper handler
is required instead of compat_ptr_ioctl.

Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
---
v3: add a better description
v2: use compat_ptr_ioctl instead of generic_compat_ioctl_ptrarg,
as suggested by Al Viro
parent da0c9ea1

fs/ioctl.c

+35 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#include <linux/syscalls.h>

#include <linux/mm.h>

#include <linux/capability.h>

#include <linux/compat.h>

#include <linux/file.h>

#include <linux/fs.h>

#include <linux/security.h>
@@ -719,3 +720,37 @@ SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd, unsigned long, arg) 
{

	return ksys_ioctl(fd, cmd, arg);

}



#ifdef CONFIG_COMPAT

/**

 * compat_ptr_ioctl - generic implementation of .compat_ioctl file operation

 *

 * This is not normally called as a function, but instead set in struct

 * file_operations as

 *

 *     .compat_ioctl = compat_ptr_ioctl,

 *

 * On most architectures, the compat_ptr_ioctl() just passes all arguments

 * to the corresponding ->ioctl handler. The exception is arch/s390, where

 * compat_ptr() clears the top bit of a 32-bit pointer value, so user space

 * pointers to the second 2GB alias the first 2GB, as is the case for

 * native 32-bit s390 user space.

 *

 * The compat_ptr_ioctl() function must therefore be used only with ioctl

 * functions that either ignore the argument or pass a pointer to a

 * compatible data type.

 *

 * If any ioctl command handled by fops->unlocked_ioctl passes a plain

 * integer instead of a pointer, or any of the passed data types

 * is incompatible between 32-bit and 64-bit architectures, a proper

 * handler is required instead of compat_ptr_ioctl.

 */

long compat_ptr_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

{

	if (!file->f_op->unlocked_ioctl)

		return -ENOIOCTLCMD;



	return file->f_op->unlocked_ioctl(file, cmd, (unsigned long)compat_ptr(arg));

}

EXPORT_SYMBOL(compat_ptr_ioctl);

#endif

include/linux/fs.h

+7 −0
Original line number Diff line number Diff line
@@ -1727,6 +1727,13 @@ int vfs_mkobj(struct dentry *, umode_t, 


extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);



#ifdef CONFIG_COMPAT

extern long compat_ptr_ioctl(struct file *file, unsigned int cmd,

					unsigned long arg);

#else

#define compat_ptr_ioctl NULL

#endif



/*

 * VFS file helper functions.

 */

CRA Git | Maintained and supported by SUSTech CRA and CCSE