[PATCH 5.15 43/69] proc: sysctl: prevent aliased sysctls from getting passed to init

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Krister Johansen <kjlx@templeofstupid.com>

commit 8001f49394e353f035306a45bcf504f06fca6355 upstream.

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

--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1780,6 +1780,13 @@ static const char *sysctl_find_alias(cha
 	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)
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -210,6 +210,7 @@ extern void __register_sysctl_init(const
 				 const char *table_name);
 #define register_sysctl_init(path, table) __register_sysctl_init(path, table, #table)
 void do_sysctl_args(void);
+bool sysctl_is_alias(char *param);
 
 extern int pwrsw_enabled;
 extern int unaligned_enabled;
@@ -251,6 +252,11 @@ static inline void setup_sysctl_set(stru
 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,
--- a/init/main.c
+++ b/init/main.c
@@ -540,6 +540,10 @@ static int __init unknown_bootoption(cha
 {
 	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 */