improve the uswsusp ioctl handling to avoid set_fs

improve the uswsusp ioctl handling to avoid set_fs

[Christoph Hellwig]

Hi all,

this series refactors the uswsusp ioctl so that no rewriting of
the ioctl structure for the compat case, and thus messing with the
address limit is required.

[PATCH 1/2] PM / sleep: move SNAPSHOT_SET_SWAP_AREA handling into a helper

[Christoph Hellwig]

Move the handling of the SNAPSHOT_SET_SWAP_AREA ioctl from the main
ioctl helper into a helper function.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 kernel/power/user.c | 57 +++++++++++++++++++++++----------------------
 1 file changed, 29 insertions(+), 28 deletions(-)

diff --git a/kernel/power/user.c b/kernel/power/user.c
index ef90eb1fb86e..0cb555f526e4 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -196,6 +196,34 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
 	return res;
 }
 
+static int snapshot_set_swap_area(struct snapshot_data *data,
+		void __user *argp)
+{
+	struct resume_swap_area swap_area;
+	sector_t offset;
+	dev_t swdev;
+
+	if (swsusp_swap_in_use())
+		return -EPERM;
+	if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
+		return -EFAULT;
+
+	/*
+	 * User space encodes device types as two-byte values,
+	 * so we need to recode them
+	 */
+	swdev = new_decode_dev(swap_area.dev);
+	if (!swdev) {
+		data->swap = -1;
+		return -EINVAL;
+	}
+	offset = swap_area.offset;
+	data->swap = swap_type_of(swdev, offset, NULL);
+	if (data->swap < 0)
+		return -ENODEV;
+	return 0;
+}
+
 static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 							unsigned long arg)
 {
@@ -351,34 +379,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		break;
 
 	case SNAPSHOT_SET_SWAP_AREA:
-		if (swsusp_swap_in_use()) {
-			error = -EPERM;
-		} else {
-			struct resume_swap_area swap_area;
-			dev_t swdev;
-
-			error = copy_from_user(&swap_area, (void __user *)arg,
-					sizeof(struct resume_swap_area));
-			if (error) {
-				error = -EFAULT;
-				break;
-			}
-
-			/*
-			 * User space encodes device types as two-byte values,
-			 * so we need to recode them
-			 */
-			swdev = new_decode_dev(swap_area.dev);
-			if (swdev) {
-				offset = swap_area.offset;
-				data->swap = swap_type_of(swdev, offset, NULL);
-				if (data->swap < 0)
-					error = -ENODEV;
-			} else {
-				data->swap = -1;
-				error = -EINVAL;
-			}
-		}
+		error = snapshot_set_swap_area(data, (void __user *)arg);
 		break;
 
 	default:
-- 
2.25.1

[PATCH 2/2] PM / sleep: handle the compat case in snapshot_set_swap_area

[Christoph Hellwig]

Use in_compat_syscall to copy directly from the 32-bit ABI structure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 kernel/power/user.c | 54 ++++++++++++++++++---------------------------
 1 file changed, 22 insertions(+), 32 deletions(-)

diff --git a/kernel/power/user.c b/kernel/power/user.c
index 0cb555f526e4..7959449765d9 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -196,28 +196,44 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
 	return res;
 }
 
+struct compat_resume_swap_area {
+	compat_loff_t offset;
+	u32 dev;
+} __packed;
+
 static int snapshot_set_swap_area(struct snapshot_data *data,
 		void __user *argp)
 {
-	struct resume_swap_area swap_area;
 	sector_t offset;
 	dev_t swdev;
 
 	if (swsusp_swap_in_use())
 		return -EPERM;
-	if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
-		return -EFAULT;
+
+	if (in_compat_syscall()) {
+		struct compat_resume_swap_area swap_area;
+
+		if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
+			return -EFAULT;
+		swdev = new_decode_dev(swap_area.dev);
+		offset = swap_area.offset;
+	} else {
+		struct resume_swap_area swap_area;
+
+		if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
+			return -EFAULT;
+		swdev = new_decode_dev(swap_area.dev);
+		offset = swap_area.offset;
+	}
 
 	/*
 	 * User space encodes device types as two-byte values,
 	 * so we need to recode them
 	 */
-	swdev = new_decode_dev(swap_area.dev);
 	if (!swdev) {
 		data->swap = -1;
 		return -EINVAL;
 	}
-	offset = swap_area.offset;
 	data->swap = swap_type_of(swdev, offset, NULL);
 	if (data->swap < 0)
 		return -ENODEV;
@@ -394,12 +410,6 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 }
 
 #ifdef CONFIG_COMPAT
-
-struct compat_resume_swap_area {
-	compat_loff_t offset;
-	u32 dev;
-} __packed;
-
 static long
 snapshot_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
@@ -410,33 +420,13 @@ snapshot_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case SNAPSHOT_AVAIL_SWAP_SIZE:
 	case SNAPSHOT_ALLOC_SWAP_PAGE:
 	case SNAPSHOT_CREATE_IMAGE:
+	case SNAPSHOT_SET_SWAP_AREA:
 		return snapshot_ioctl(file, cmd,
 				      (unsigned long) compat_ptr(arg));
-
-	case SNAPSHOT_SET_SWAP_AREA: {
-		struct compat_resume_swap_area __user *u_swap_area =
-			compat_ptr(arg);
-		struct resume_swap_area swap_area;
-		mm_segment_t old_fs;
-		int err;
-
-		err = get_user(swap_area.offset, &u_swap_area->offset);
-		err |= get_user(swap_area.dev, &u_swap_area->dev);
-		if (err)
-			return -EFAULT;
-		old_fs = get_fs();
-		set_fs(KERNEL_DS);
-		err = snapshot_ioctl(file, SNAPSHOT_SET_SWAP_AREA,
-				     (unsigned long) &swap_area);
-		set_fs(old_fs);
-		return err;
-	}
-
 	default:
 		return snapshot_ioctl(file, cmd, arg);
 	}
 }
-
 #endif /* CONFIG_COMPAT */
 
 static const struct file_operations snapshot_fops = {
-- 
2.25.1

Re: [PATCH 2/2] PM / sleep: handle the compat case in snapshot_set_swap_area

[Rafael J. Wysocki]

On Mon, Apr 6, 2020 at 1:58 PM Christoph Hellwig <hch@lst.de> wrote:
>
> Use in_compat_syscall to copy directly from the 32-bit ABI structure.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  kernel/power/user.c | 54 ++++++++++++++++++---------------------------
>  1 file changed, 22 insertions(+), 32 deletions(-)
>
> diff --git a/kernel/power/user.c b/kernel/power/user.c
> index 0cb555f526e4..7959449765d9 100644
> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -196,28 +196,44 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
>         return res;
>  }
>
> +struct compat_resume_swap_area {
> +       compat_loff_t offset;
> +       u32 dev;
> +} __packed;
> +
>  static int snapshot_set_swap_area(struct snapshot_data *data,
>                 void __user *argp)
>  {
> -       struct resume_swap_area swap_area;
>         sector_t offset;
>         dev_t swdev;
>
>         if (swsusp_swap_in_use())
>                 return -EPERM;
> -       if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
> -               return -EFAULT;
> +
> +       if (in_compat_syscall()) {
> +               struct compat_resume_swap_area swap_area;
> +
> +               if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
> +                       return -EFAULT;
> +               swdev = new_decode_dev(swap_area.dev);
> +               offset = swap_area.offset;
> +       } else {
> +               struct resume_swap_area swap_area;
> +
> +               if (copy_from_user(&swap_area, argp, sizeof(swap_area)))
> +                       return -EFAULT;
> +               swdev = new_decode_dev(swap_area.dev);
> +               offset = swap_area.offset;
> +       }
>
>         /*
>          * User space encodes device types as two-byte values,
>          * so we need to recode them
>          */
> -       swdev = new_decode_dev(swap_area.dev);
>         if (!swdev) {
>                 data->swap = -1;
>                 return -EINVAL;
>         }
> -       offset = swap_area.offset;
>         data->swap = swap_type_of(swdev, offset, NULL);
>         if (data->swap < 0)
>                 return -ENODEV;
> @@ -394,12 +410,6 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
>  }
>
>  #ifdef CONFIG_COMPAT
> -
> -struct compat_resume_swap_area {
> -       compat_loff_t offset;
> -       u32 dev;
> -} __packed;
> -
>  static long
>  snapshot_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>  {
> @@ -410,33 +420,13 @@ snapshot_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>         case SNAPSHOT_AVAIL_SWAP_SIZE:
>         case SNAPSHOT_ALLOC_SWAP_PAGE:
>         case SNAPSHOT_CREATE_IMAGE:
> +       case SNAPSHOT_SET_SWAP_AREA:
>                 return snapshot_ioctl(file, cmd,
>                                       (unsigned long) compat_ptr(arg));
> -
> -       case SNAPSHOT_SET_SWAP_AREA: {
> -               struct compat_resume_swap_area __user *u_swap_area =
> -                       compat_ptr(arg);
> -               struct resume_swap_area swap_area;
> -               mm_segment_t old_fs;
> -               int err;
> -
> -               err = get_user(swap_area.offset, &u_swap_area->offset);
> -               err |= get_user(swap_area.dev, &u_swap_area->dev);
> -               if (err)
> -                       return -EFAULT;
> -               old_fs = get_fs();
> -               set_fs(KERNEL_DS);
> -               err = snapshot_ioctl(file, SNAPSHOT_SET_SWAP_AREA,
> -                                    (unsigned long) &swap_area);
> -               set_fs(old_fs);
> -               return err;
> -       }
> -
>         default:
>                 return snapshot_ioctl(file, cmd, arg);
>         }
>  }
> -
>  #endif /* CONFIG_COMPAT */
>
>  static const struct file_operations snapshot_fops = {
> --

Applied along with the [1/2] as 5.7-rc material, thanks!