[PATCH RFC v4 07/25] crypto: ccp: use scoped_with_init_fs() for SEV file access

[Christian Brauner <brauner@kernel.org>]

Replace the manual init_task root retrieval with scoped_with_init_fs()
to temporarily override current->fs. This allows using the simpler
filp_open() instead of the init_root() + file_open_root() pattern.

open_file_as_root() ← sev_read_init_ex_file() / sev_write_init_ex_file()
← sev_platform_init() ← __sev_guest_init() ← KVM ioctl — user process context

Needs init's root because the SEV init_ex file path should resolve
against the real root, not a KVM user's chroot.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 drivers/crypto/ccp/sev-dev.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index d1e9e0ac63b6..b99737f7f571 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -260,20 +260,16 @@ static int sev_cmd_buffer_len(int cmd)
 
 static struct file *open_file_as_root(const char *filename, int flags, umode_t mode)
 {
-	struct path root __free(path_put) = {};
-
-	task_lock(&init_task);
-	get_fs_root(init_task.fs, &root);
-	task_unlock(&init_task);
-
 	CLASS(prepare_creds, cred)();
 	if (!cred)
 		return ERR_PTR(-ENOMEM);
 
 	cred->fsuid = GLOBAL_ROOT_UID;
 
-	scoped_with_creds(cred)
-		return file_open_root(&root, filename, flags, mode);
+	scoped_with_init_fs() {
+		scoped_with_creds(cred)
+			return filp_open(filename, flags, mode);
+	}
 }
 
 static int sev_read_init_ex_file(void)

-- 
2.47.3