mtd: provide proper 32/64-bit compat_ioctl() support for BLKPG

After a bit of poking around wondering why my 32-bit user-space can't
seem to send a proper ioctl(BLKPG) to an MTD on my 64-bit kernel
(ARM64), I noticed that struct blkpg_ioctl_arg is actually pretty
unsuitable for use in the ioctl() ABI, due to its use of raw pointers,
and its lack of alignment/packing restrictions (32-bit arch'es tend to
pack the 4 fields into 4 32-bit words, whereas 64-bit arch'es would add
padding after the third int, and make this 6 32-bit words).

Anyway, this means BLKPG deserves some special compat_ioctl handling. Do
the conversion in a small shim for MTD.

block/compat_ioctl.c already has compat support for the block subsystem,
but it does so by a re-marshalling data to/from user-space (see
compat_blkpg_ioctl()). Personally, I think this approach is cleaner.

Tested only on MTD, with an ARM32 user space on an ARM64 kernel.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 55fa27ecf4e15203f83808c87fc5cea8f18661b4..6d19835b80a952e098cfdfa8436971d5c68a593e 100644 (file)
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -498,21 +498,17 @@ static int shrink_ecclayout(const struct nand_ecclayout *from,
 }
 
 static int mtdchar_blkpg_ioctl(struct mtd_info *mtd,
-                          struct blkpg_ioctl_arg __user *arg)
+                              struct blkpg_ioctl_arg *arg)
 {
-       struct blkpg_ioctl_arg a;
        struct blkpg_partition p;
 
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
 
-       if (copy_from_user(&a, arg, sizeof(struct blkpg_ioctl_arg)))
+       if (copy_from_user(&p, arg->data, sizeof(p)))
                return -EFAULT;
 
-       if (copy_from_user(&p, a.data, sizeof(struct blkpg_partition)))
-               return -EFAULT;
-
-       switch (a.op) {
+       switch (arg->op) {
        case BLKPG_ADD_PARTITION:
 
                /* Only master mtd device must be used to add partitions */
@@ -966,8 +962,13 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 
        case BLKPG:
        {
-               ret = mtdchar_blkpg_ioctl(mtd,
-                     (struct blkpg_ioctl_arg __user *)arg);
+               struct blkpg_ioctl_arg __user *blk_arg = argp;
+               struct blkpg_ioctl_arg a;
+
+               if (copy_from_user(&a, blk_arg, sizeof(a)))
+                       ret = -EFAULT;
+               else
+                       ret = mtdchar_blkpg_ioctl(mtd, &a);
                break;
        }
 
@@ -1046,6 +1047,29 @@ static long mtdchar_compat_ioctl(struct file *file, unsigned int cmd,
                                &buf_user->start);
                break;
        }
+
+       case BLKPG:
+       {
+               /* Convert from blkpg_compat_ioctl_arg to blkpg_ioctl_arg */
+               struct blkpg_compat_ioctl_arg __user *uarg = argp;
+               struct blkpg_compat_ioctl_arg compat_arg;
+               struct blkpg_ioctl_arg a;
+
+               if (copy_from_user(&compat_arg, uarg, sizeof(compat_arg))) {
+                       ret = -EFAULT;
+                       break;
+               }
+
+               memset(&a, 0, sizeof(a));
+               a.op = compat_arg.op;
+               a.flags = compat_arg.flags;
+               a.datalen = compat_arg.datalen;
+               a.data = compat_ptr(compat_arg.data);
+
+               ret = mtdchar_blkpg_ioctl(mtd, &a);
+               break;
+       }
+
        default:
                ret = mtdchar_ioctl(file, cmd, (unsigned long)argp);
        }

diff --git a/include/linux/blkpg.h b/include/linux/blkpg.h
new file mode 100644 (file)
index 0000000..bef124f
--- /dev/null
+++ b/include/linux/blkpg.h
@@ -0,0 +1,21 @@
+#ifndef _LINUX_BLKPG_H
+#define _LINUX_BLKPG_H
+
+/*
+ * Partition table and disk geometry handling
+ */
+
+#include <linux/compat.h>
+#include <uapi/linux/blkpg.h>
+
+#ifdef CONFIG_COMPAT
+/* For 32-bit/64-bit compatibility of struct blkpg_ioctl_arg */
+struct blkpg_compat_ioctl_arg {
+       compat_int_t op;
+       compat_int_t flags;
+       compat_int_t datalen;
+       compat_uptr_t data;
+};
+#endif
+
+#endif /* _LINUX_BLKPG_H */

diff --git a/include/uapi/linux/blkpg.h b/include/uapi/linux/blkpg.h
index a8519446c111ab02fb71e79e6b31fea1df666223..63739a035085f9746389853a74839b4ad85aaf1a 100644 (file)
--- a/include/uapi/linux/blkpg.h
+++ b/include/uapi/linux/blkpg.h
@@ -1,5 +1,5 @@
-#ifndef _LINUX_BLKPG_H
-#define _LINUX_BLKPG_H
+#ifndef _UAPI__LINUX_BLKPG_H
+#define _UAPI__LINUX_BLKPG_H
 
 /*
  * Partition table and disk geometry handling
@@ -56,4 +56,4 @@ struct blkpg_partition {
        char volname[BLKPG_VOLNAMELTH]; /* volume label */
 };
 
-#endif /* _LINUX_BLKPG_H */
+#endif /* _UAPI__LINUX_BLKPG_H */