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Message-Id: <20240511-sysctl-const-table-arg-ucount-v1-1-a00ad8f6f233@weissschuh.net>
Date: Sat, 11 May 2024 21:28:10 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: linux-kernel@...r.kernel.org
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
Joel Granados <j.granados@...sung.com>,
Luis Chamberlain <mcgrof@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH] ucounts: constify usage of ctl_table_header::ctl_table_arg
The sysctl core is preparing to only expose instances of
struct ctl_table as "const".
This will also affect the member
ctl_table_header::ctl_table_arg.
Prepare for that change to "struct ctl_table_header",
and already constify the usage of ctl_table_arg.
No functional change.
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
Motivation
==========
Moving structures containing function pointers into unmodifiable .rodata
prevents attackers or bugs from corrupting and diverting those pointers.
Also the "struct ctl_table" exposed by the sysctl core were never meant
to be mutated by users.
Process
=======
* Drop ctl_table modifications from the sysctl core ([0], in -next)
* Constify arguments to ctl_table_root::{set_ownership,permissions}
([1], in -next)
* Migrate users of "ctl_table_header::ctl_table_arg" to "const".
(in progress, this patch)
* Afterwards convert "ctl_table_header::ctl_table_arg" itself to const.
(to be done)
* Prepare helpers used to implement proc_handlers throughout the tree to
use "const struct ctl_table *". ([2], in progress)
* Afterwards switch over all proc_handlers callbacks to use
"const struct ctl_table *" in one commit. ([2], in progress)
Only custom handlers will be affected, the big commit avoids a
disruptive and messy transition phase.
* Switch over the internals of the sysctl core to "const struct ctl_table *" (to be done)
* Switch include/linux/sysctl.h to "const struct ctl_table *" (to be done)
* Transition instances of "struct ctl_table" through the tree to const (to be done)
A work-in-progress view containging all the outlined changes can be found at
https://git.sr.ht/~t-8ch/linux sysctl-constfy
[0] https://lore.kernel.org/lkml/20240322-sysctl-empty-dir-v2-0-e559cf8ec7c0@weissschuh.net/
[1] https://lore.kernel.org/lkml/20240315-sysctl-const-ownership-v3-0-b86680eae02e@weissschuh.net/
[2] https://lore.kernel.org/lkml/20240423-sysctl-const-handler-v3-0-e0beccb836e2@weissschuh.net/
Cc: Joel Granados <j.granados@...sung.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
---
kernel/ucount.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 4aa6166cb856..d9e283600f5c 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -119,7 +119,7 @@ bool setup_userns_sysctls(struct user_namespace *ns)
void retire_userns_sysctls(struct user_namespace *ns)
{
#ifdef CONFIG_SYSCTL
- struct ctl_table *tbl;
+ const struct ctl_table *tbl;
tbl = ns->sysctls->ctl_table_arg;
unregister_sysctl_table(ns->sysctls);
---
base-commit: cf87f46fd34d6c19283d9625a7822f20d90b64a4
change-id: 20240511-sysctl-const-table-arg-ucount-75027ec3fbf4
Best regards,
--
Thomas Weißschuh <linux@...ssschuh.net>
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