[PATCH v2 2/2] fuse: Support FS_IOC_GET_ENCRYPTION_POLICY_EX

[Chirantan Ekbote <chirantan@chromium.org>]

Chrome OS would like to support this ioctl when passed through the fuse
driver. However since it is dynamically sized, we can't rely on the
length encoded in the command.  Instead check the `policy_size` field of
the user provided parameter to get the max length of the data returned
by the server.

Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
---
 fs/fuse/file.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 69cffb77a0b25..b64ff7f2fe4dd 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -19,6 +19,7 @@
 #include <linux/falloc.h>
 #include <linux/uio.h>
 #include <linux/fs.h>
+#include <linux/fscrypt.h>
 
 static struct page **fuse_pages_alloc(unsigned int npages, gfp_t flags,
 				      struct fuse_page_desc **desc)
@@ -2710,6 +2711,21 @@ static int fuse_get_ioctl_len(unsigned int cmd, unsigned long arg, size_t *len)
 	case FS_IOC_SETFLAGS:
 		*len = sizeof(int);
 		break;
+	case FS_IOC_GET_ENCRYPTION_POLICY_EX: {
+		__u64 policy_size;
+		struct fscrypt_get_policy_ex_arg __user *uarg =
+			(struct fscrypt_get_policy_ex_arg __user *)arg;
+
+		if (copy_from_user(&policy_size, &uarg->policy_size,
+				   sizeof(policy_size)))
+			return -EFAULT;
+
+		if (policy_size > SIZE_MAX - sizeof(policy_size))
+			return -EINVAL;
+
+		*len = sizeof(policy_size) + policy_size;
+		break;
+	}
 	default:
 		*len = _IOC_SIZE(cmd);
 		break;
-- 
2.29.2.576.ga3fc446d84-goog