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authorDmitry Safonov <dima@arista.com>2020-03-02 17:51:34 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-03-07 09:52:02 +0100
commiteaee41727e6d8a7d2b94421c25e82b00cb2fded5 (patch)
tree1b9f0cdd393854d1d8cc5bfc58c895a1d06f0f5a
parent7f9803072ff636fc22ad941ff059e020e9d77ed4 (diff)
sysctl/sysrq: Remove __sysrq_enabled copy
Many embedded boards have a disconnected TTL level serial which can generate some garbage that can lead to spurious false sysrq detects. Currently, sysrq can be either completely disabled for serial console or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port") At Arista, we have such boards that can generate BREAK and random garbage. While disabling sysrq for serial console would solve the problem with spurious false sysrq triggers, it's also desirable to have a way to enable sysrq back. Having the way to enable sysrq was beneficial to debug lockups with a manual investigation in field and on the other side preventing false sysrq detections. As a preparation to add sysrq_toggle_support() call into uart, remove a private copy of sysrq_enabled from sysctl - it should reflect the actual status of sysrq. Furthermore, the private copy isn't correct already in case sysrq_always_enabled is true. So, remove __sysrq_enabled and use a getter-helper sysrq_mask() to check sysrq_key_op enabled status. Cc: Iurii Zaikin <yzaikin@google.com> Cc: Jiri Slaby <jslaby@suse.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Dmitry Safonov <dima@arista.com> Link: https://lore.kernel.org/r/20200302175135.269397-2-dima@arista.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/sysrq.c12
-rw-r--r--include/linux/sysrq.h7
-rw-r--r--kernel/sysctl.c41
3 files changed, 41 insertions, 19 deletions
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index f724962a5906..5e0d0813da55 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -63,6 +63,18 @@ static bool sysrq_on(void)
return sysrq_enabled || sysrq_always_enabled;
}
+/**
+ * sysrq_mask - Getter for sysrq_enabled mask.
+ *
+ * Return: 1 if sysrq is always enabled, enabled sysrq_key_op mask otherwise.
+ */
+int sysrq_mask(void)
+{
+ if (sysrq_always_enabled)
+ return 1;
+ return sysrq_enabled;
+}
+
/*
* A value of 1 means 'all', other nonzero values are an op mask:
*/
diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
index 8c71874e8485..8e159e16850f 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -50,6 +50,7 @@ int unregister_sysrq_key(int key, struct sysrq_key_op *op);
struct sysrq_key_op *__sysrq_get_key_op(int key);
int sysrq_toggle_support(int enable_mask);
+int sysrq_mask(void);
#else
@@ -71,6 +72,12 @@ static inline int unregister_sysrq_key(int key, struct sysrq_key_op *op)
return -EINVAL;
}
+static inline int sysrq_mask(void)
+{
+ /* Magic SysRq disabled mask */
+ return 0;
+}
+
#endif
#endif /* _LINUX_SYSRQ_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ad5b88a53c5a..94638f695e60 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -229,25 +229,8 @@ static int proc_dopipe_max_size(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos);
#ifdef CONFIG_MAGIC_SYSRQ
-/* Note: sysrq code uses its own private copy */
-static int __sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
-
static int sysrq_sysctl_handler(struct ctl_table *table, int write,
- void __user *buffer, size_t *lenp,
- loff_t *ppos)
-{
- int error;
-
- error = proc_dointvec(table, write, buffer, lenp, ppos);
- if (error)
- return error;
-
- if (write)
- sysrq_toggle_support(__sysrq_enabled);
-
- return 0;
-}
-
+ void __user *buffer, size_t *lenp, loff_t *ppos);
#endif
static struct ctl_table kern_table[];
@@ -747,7 +730,7 @@ static struct ctl_table kern_table[] = {
#ifdef CONFIG_MAGIC_SYSRQ
{
.procname = "sysrq",
- .data = &__sysrq_enabled,
+ .data = NULL,
.maxlen = sizeof (int),
.mode = 0644,
.proc_handler = sysrq_sysctl_handler,
@@ -2835,6 +2818,26 @@ static int proc_dostring_coredump(struct ctl_table *table, int write,
}
#endif
+#ifdef CONFIG_MAGIC_SYSRQ
+static int sysrq_sysctl_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ int tmp, ret;
+
+ tmp = sysrq_mask();
+
+ ret = __do_proc_dointvec(&tmp, table, write, buffer,
+ lenp, ppos, NULL, NULL);
+ if (ret || !write)
+ return ret;
+
+ if (write)
+ sysrq_toggle_support(tmp);
+
+ return 0;
+}
+#endif
+
static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int write,
void __user *buffer,
size_t *lenp, loff_t *ppos,