[PATCH] sysctl: treewide: constify ctl_table_root::permissions

[Thomas Weißschuh <linux@xxxxxxxxxxxxxx>]

The permissions callback is not supposed to modify the ctl_table.
Enforce this expectation via the typesystem.

The patch was created with the following coccinelle script:

  virtual patch
  virtual context
  virtual report

  @@
  identifier func, head, ctl;
  @@

  int func(
    struct ctl_table_header *head,
  - struct ctl_table *ctl)
  + const struct ctl_table *ctl)
  { ... }

(insert_entry() from fs/proc/proc_sysctl.c is a false-positive)

This change also is a step to put "struct ctl_table" into .rodata
throughout the kernel.

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
The patch is meant to be merged via the sysctl tree.

This change was originally part of the sysctl-const series [0].
To slim down that series and reduce the message load on other
maintainers to a minimumble, submit this patch on its own.

[0] https://lore.kernel.org/lkml/20231204-const-sysctl-v2-2-7a5060b11447@xxxxxxxxxxxxxx/
---
 include/linux/sysctl.h | 2 +-
 ipc/ipc_sysctl.c       | 2 +-
 kernel/ucount.c        | 2 +-
 net/sysctl_net.c       | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 26a38161c28f..8ec2d742c3b4 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -207,7 +207,7 @@ struct ctl_table_root {
 	void (*set_ownership)(struct ctl_table_header *head,
 			      struct ctl_table *table,
 			      kuid_t *uid, kgid_t *gid);
-	int (*permissions)(struct ctl_table_header *head, struct ctl_table *table);
+	int (*permissions)(struct ctl_table_header *head, const struct ctl_table *table);
 };
 
 /* struct ctl_path describes where in the hierarchy a table is added */
diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index 8c62e443f78b..b087787f608f 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -190,7 +190,7 @@ static int set_is_seen(struct ctl_table_set *set)
 	return &current->nsproxy->ipc_ns->ipc_set == set;
 }
 
-static int ipc_permissions(struct ctl_table_header *head, struct ctl_table *table)
+static int ipc_permissions(struct ctl_table_header *head, const struct ctl_table *table)
 {
 	int mode = table->mode;
 
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 4aa6166cb856..90300840256b 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -38,7 +38,7 @@ static int set_is_seen(struct ctl_table_set *set)
 }
 
 static int set_permissions(struct ctl_table_header *head,
-				  struct ctl_table *table)
+			   const struct ctl_table *table)
 {
 	struct user_namespace *user_ns =
 		container_of(head->set, struct user_namespace, set);
diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index 051ed5f6fc93..ba9a49de9600 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -40,7 +40,7 @@ static int is_seen(struct ctl_table_set *set)
 
 /* Return standard mode bits for table entry. */
 static int net_ctl_permissions(struct ctl_table_header *head,
-			       struct ctl_table *table)
+			       const struct ctl_table *table)
 {
 	struct net *net = container_of(head->set, struct net, sysctls);
 

---
base-commit: de2ee5e9405e12600c81e39837362800cee433a2
change-id: 20231226-sysctl-const-permissions-d7cfd02a7637

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