[PATCH v2] sysctl: treewide: constify ctl_table_root::permissions

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:

  @@
  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)

The three changed locations were validated through manually inspection
and compilation.

In addition a search for '.permissions =' was done over the full tree to
look for places that were missed by coccinelle.
None were found.

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

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
To: Luis Chamberlain <mcgrof@kernel.org>
To: Kees Cook <redacted>
To: Joel Granados <redacted>
To: David S. Miller <davem@davemloft.net>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Changes in v2:
- flesh out commit messages
- Integrate changes to set_ownership and ctl_table_args into a single
  series
- Link to v1: https://lore.kernel.org/r/20231226-sysctl-const-permissions-v1-1-5cd3c91f6299@weissschuh.net (local)
---
The patch is meant to be merged via the sysctl tree.

There is an upcoming series that will introduce a new implementation of
.permission which would need to be adapted [0].
The adaption would be trivial as the 'table' parameter also not modified
there.

This change was originally part of the sysctl-const series [1].
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/20240222160915.315255-1-aleksandr.mikhalitsyn@canonical.com/ (local)
[1] https://lore.kernel.org/lkml/20231204-const-sysctl-v2-2-7a5060b11447@weissschuh.net/ (local)
---
 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 ee7d33b89e9e..0a55b5aade16 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);
 };
 
 #define register_sysctl(path, table)	\

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: ffd2cb6b718e189e7e2d5d0c19c25611f92e061a
change-id: 20231226-sysctl-const-permissions-d7cfd02a7637

Best regards,
-- 
Thomas Weißschuh [off-list ref]