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

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Date: Fri, 22 Mar 2024 13:32:46 +0100
From: Joel Granados <j.granados@...sung.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
CC: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <keescook@...omium.org>,
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] sysctl: treewide: constify argument
 ctl_table_root::permissions(table)

On Fri, Mar 15, 2024 at 07:11:31PM +0100, Thomas Weißschuh wrote:
> 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.
Will remove this when I add it to constfy branch as it is unclear (for
me) what "manually inspection" is and also I do not know what config you
used to compile. IMO, we can just do without it.

> 
> 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.

This LGTM. Will add this to the constfy testing branch with these
changes in the commit message:
"""
sysctl: treewide: constify argument ctl_table_root::permissions(table)

The permissions callback should not modify the ctl_table. Enforce this
expectation via the typesystem. This is a step to put "struct ctl_table"
into .rodata throughout the kernel.

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)

No additional occurances of '.permissions =' were found after a
tree-wide search for places missed by the conccinelle script.

"""

Reviewed-by: Joel Granados <j.granados@...sung.com>
> 
> 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
> 

-- 

Joel Granados

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