[PATCH v3] nsfs: add compat ioctl handler

[Thomas Weißschuh]

As all parameters and return values of the ioctls have the same
representation on both 32bit and 64bit we can reuse the normal ioctl
handler for the compat handler via compat_ptr_ioctl().

All nsfs ioctls return a plain "int" filedescriptor which is a signed
4-byte integer type on both 32bit and 64bit.
The only parameter taken is by NS_GET_OWNER_UID and is a pointer to a
"uid_t" which is a 4-byte unsigned integer type on both 32bit and 64bit.

Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
Reported-by: Karel Zak <kzak@xxxxxxxxxx>
Link: https://github.com/util-linux/util-linux/pull/1924#issuecomment-1344133656
Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
Changes in v3:
- Resend without changes
  v1 and v2 did not reach the mailing lists due to an issue in my mail setup
- Link to v2: https://lore.kernel.org/r/20221214-nsfs-ioctl-compat-v2-0-b295bb3913f6@xxxxxxxxxxxxxx

Changes in v2:
- Use compat_ptr_ioctl()
- Link to v1: https://lore.kernel.org/r/20221214-nsfs-ioctl-compat-v1-0-b169796000b2@xxxxxxxxxxxxxx
---
 fs/nsfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 3506f6074288..c28f69edef97 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
 static const struct file_operations ns_file_operations = {
 	.llseek		= no_llseek,
 	.unlocked_ioctl = ns_ioctl,
+	.compat_ioctl   = compat_ptr_ioctl,
 };
 
 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)

---
base-commit: f9ff5644bcc04221bae56f922122f2b7f5d24d62
change-id: 20221214-nsfs-ioctl-compat-1548bf6581a7

Best regards,
-- 
Thomas Weißschuh <linux@xxxxxxxxxxxxxx>