firmware: enable run time change of forcing fallback loader

Currently one requires to test four kernel configurations to test the
firmware API completely:

0)
  CONFIG_FW_LOADER=y

1)
  o CONFIG_FW_LOADER=y
  o CONFIG_FW_LOADER_USER_HELPER=y

2)
  o CONFIG_FW_LOADER=y
  o CONFIG_FW_LOADER_USER_HELPER=y
  o CONFIG_FW_LOADER_USER_HELPER_FALLBACK=y

3) When CONFIG_FW_LOADER=m the built-in stuff is disabled, we have
   no current tests for this.

We can reduce the requirements to three kernel configurations by making
fw_config.force_sysfs_fallback a proc knob we flip on off. For kernels that
disable CONFIG_IKCONFIG_PROC this can also enable one to inspect if
CONFIG_FW_LOADER_USER_HELPER_FALLBACK was enabled at build time by checking
the proc value at boot time.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/base/firmware_loader/fallback_table.c b/drivers/base/firmware_loader/fallback_table.c
index 981419044c7e..92365e053e30 100644
--- a/drivers/base/firmware_loader/fallback_table.c
+++ b/drivers/base/firmware_loader/fallback_table.c
@@ -19,6 +19,9 @@
 /* Module or buit-in */
 #ifdef CONFIG_FW_LOADER_USER_HELPER
 
+static unsigned int zero;
+static unsigned int one = 1;
+
 struct firmware_fallback_config fw_fallback_config = {
         .force_sysfs_fallback = IS_ENABLED(CONFIG_FW_LOADER_USER_HELPER_FALLBACK),
         .loading_timeout = 60,
@@ -26,4 +29,18 @@ struct firmware_fallback_config fw_fallback_config = {
 };
 EXPORT_SYMBOL_GPL(fw_fallback_config);
 
+struct ctl_table firmware_config_table[] = {
+        {
+                .procname       = "force_sysfs_fallback",
+                .data           = &fw_fallback_config.force_sysfs_fallback,
+                .maxlen         = sizeof(unsigned int),
+                .mode           = 0644,
+                .proc_handler   = proc_douintvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &one,
+        },
+        { }
+};
+EXPORT_SYMBOL_GPL(firmware_config_table);
+
 #endif