[PATCH RFC v4 08/25] scsi: target: use scoped_with_init_fs() for ALUA metadata

[Christian Brauner <brauner@kernel.org>]

core_alua_write_tpg_metadata() can be called from both kthread and user
process context. Use scoped_with_init_fs() to temporarily override
current->fs for the filp_open() call when running in kthread context so
the path lookup happens in init's filesystem context.

core_alua_write_tpg_metadata() ← core_alua_update_tpg_primary_metadata()
← core_alua_do_transition_tg_pt() ← target_queued_submit_work() ←
kworker (target submission workqueue)

Also reached synchronously from configfs (user process) via the
alua_access_state and alua_tg_pt_offline attributes:

core_alua_write_tpg_metadata() ← core_alua_update_tpg_primary_metadata()
← core_alua_do_transition_tg_pt() ← core_alua_do_port_transition() ←
target_tg_pt_gp_alua_access_state_store()

In that case current->fs must not be overridden as the path should
resolve against the calling process's filesystem root.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 drivers/target/target_core_alua.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/target/target_core_alua.c b/drivers/target/target_core_alua.c
index 10250aca5a81..140154d93c43 100644
--- a/drivers/target/target_core_alua.c
+++ b/drivers/target/target_core_alua.c
@@ -18,6 +18,8 @@
 #include <linux/fcntl.h>
 #include <linux/file.h>
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
+#include <linux/kthread.h>
 #include <scsi/scsi_proto.h>
 #include <linux/unaligned.h>
 
@@ -856,10 +858,17 @@ static int core_alua_write_tpg_metadata(
 	unsigned char *md_buf,
 	u32 md_buf_len)
 {
-	struct file *file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600);
+	struct file *file;
 	loff_t pos = 0;
 	int ret;
 
+	if (tsk_is_kthread(current)) {
+		scoped_with_init_fs()
+			file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600);
+	} else {
+		file = filp_open(path, O_RDWR | O_CREAT | O_TRUNC, 0600);
+	}
+
 	if (IS_ERR(file)) {
 		pr_err("filp_open(%s) for ALUA metadata failed\n", path);
 		return -ENODEV;

-- 
2.47.3