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fs: Add compat_ptr_ioctl()

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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.

Change-Id: Ic216898976f9369d6f8a316bf75eb9d8a00386fe
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Richard Raya <rdxzv.dev@gmail.com>
This commit is contained in:
Arnd Bergmann 2018-09-11 16:55:03 +02:00 committed by Richard Raya
parent ba1344d216
commit 0876ea375c
2 changed files with 42 additions and 0 deletions
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35
fs/ioctl.c
View File

@ -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>
@ -730,3 +731,37 @@ SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd, unsigned long, arg)
fdput(f);
return error;
}
#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

7
include/linux/fs.h
View File

@ -1658,6 +1658,13 @@ extern struct dentry *vfs_tmpfile(struct vfsmount *mnt,
struct dentry *dentry, umode_t mode,
int open_flag);
#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.
*/