linux-kernel - [PATCH 1/2] proc: sysctl: prevent aliased sysctls from getting passed to init

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Date:   Fri, 27 Oct 2023 14:46:40 -0700
From:   Krister Johansen <kjlx@...pleofstupid.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Douglas Anderson <dianders@...omium.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Arnd Bergmann <arnd@...db.de>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Hildenbrand <david@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pingfan Liu <kernelfans@...il.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        "Guilherme G. Piccoli" <kernel@...ccoli.net>,
        Mike Rapoport <rppt@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 1/2] proc: sysctl: prevent aliased sysctls from getting
 passed to init

The code that checks for unknown boot options is unaware of the sysctl
alias facility, which maps bootparams to sysctl values.  If a user sets
an old value that has a valid alias, a message about an invalid
parameter will be printed during boot, and the parameter will get passed
to init.  Fix by checking for the existence of aliased parameters in the
unknown boot parameter code.  If an alias exists, don't return an error
or pass the value to init.

Signed-off-by: Krister Johansen <kjlx@...pleofstupid.com>
Cc: stable@...r.kernel.org
Fixes: 0a477e1ae21b ("kernel/sysctl: support handling command line aliases")
---
 fs/proc/proc_sysctl.c  | 7 +++++++
 include/linux/sysctl.h | 6 ++++++
 init/main.c            | 4 ++++
 3 files changed, 17 insertions(+)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index c88854df0b62..1c9635dddb70 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1592,6 +1592,13 @@ static const char *sysctl_find_alias(char *param)
 	return NULL;
 }
 
+bool sysctl_is_alias(char *param)
+{
+	const char *alias = sysctl_find_alias(param);
+
+	return alias != NULL;
+}
+
 /* Set sysctl value passed on kernel command line. */
 static int process_sysctl_arg(char *param, char *val,
 			       const char *unused, void *arg)
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 09d7429d67c0..61b40ea81f4d 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -242,6 +242,7 @@ extern void __register_sysctl_init(const char *path, struct ctl_table *table,
 extern struct ctl_table_header *register_sysctl_mount_point(const char *path);
 
 void do_sysctl_args(void);
+bool sysctl_is_alias(char *param);
 int do_proc_douintvec(struct ctl_table *table, int write,
 		      void *buffer, size_t *lenp, loff_t *ppos,
 		      int (*conv)(unsigned long *lvalp,
@@ -287,6 +288,11 @@ static inline void setup_sysctl_set(struct ctl_table_set *p,
 static inline void do_sysctl_args(void)
 {
 }
+
+static inline bool sysctl_is_alias(char *param)
+{
+	return false;
+}
 #endif /* CONFIG_SYSCTL */
 
 int sysctl_max_threads(struct ctl_table *table, int write, void *buffer,
diff --git a/init/main.c b/init/main.c
index 436d73261810..e24b0780fdff 100644
--- a/init/main.c
+++ b/init/main.c
@@ -530,6 +530,10 @@ static int __init unknown_bootoption(char *param, char *val,
 {
 	size_t len = strlen(param);
 
+	/* Handle params aliased to sysctls */
+	if (sysctl_is_alias(param))
+		return 0;
+
 	repair_env_string(param, val);
 
 	/* Handle obsolete-style parameters */
-- 
2.25.1