linux-kernel - [PATCH v3 2/2] sysctl: treewide: constify argument ctl_table

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Message-Id: <20240315-sysctl-const-ownership-v3-2-b86680eae02e@weissschuh.net>
Date: Fri, 15 Mar 2024 19:11:31 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <keescook@...omium.org>, 
 Joel Granados <j.granados@...sung.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v3 2/2] sysctl: treewide: constify argument
 ctl_table_root::permissions(table)

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@...ssschuh.net>
---
 include/linux/sysctl.h | 2 +-
 ipc/ipc_sysctl.c       | 2 +-
 ipc/mq_sysctl.c        | 2 +-
 kernel/ucount.c        | 2 +-
 net/sysctl_net.c       | 2 +-
 5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 60333a6b9370..f9214de0490c 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -206,7 +206,7 @@ struct ctl_table_root {
 	struct ctl_table_set *(*lookup)(struct ctl_table_root *root);
 	void (*set_ownership)(struct ctl_table_header *head,
 			      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 1a5085e5b178..19b2a67aef40 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -204,7 +204,7 @@ static void ipc_set_ownership(struct ctl_table_header *head,
 	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
 }
 
-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/ipc/mq_sysctl.c b/ipc/mq_sysctl.c
index 6bb1c5397c69..43c0825da9e8 100644
--- a/ipc/mq_sysctl.c
+++ b/ipc/mq_sysctl.c
@@ -90,7 +90,7 @@ static void mq_set_ownership(struct ctl_table_header *head,
 	*gid = gid_valid(ns_root_gid) ? ns_root_gid : GLOBAL_ROOT_GID;
 }
 
-static int mq_permissions(struct ctl_table_header *head, struct ctl_table *table)
+static int mq_permissions(struct ctl_table_header *head, const struct ctl_table *table)
 {
 	int mode = table->mode;
 	kuid_t ns_root_uid;
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 a0a7a79991f9..f5017012a049 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);
 

-- 
2.44.0