[PATCH v2] kern: perform NULL check in unregister paths (command/extcmd)

[Srish Srinivasan <ssrish@linux.ibm.com>]

Many modules call grub_unregister_{command(), extcmd()} from
GRUB_MOD_FINI() without checking for a failure in registration.
This could lead to a NULL pointer dereference in unregistration.

Perform explicit NULL check in both the unregister helpers.

Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
---
 grub-core/commands/extcmd.c | 3 +++
 grub-core/kern/command.c    | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/grub-core/commands/extcmd.c b/grub-core/commands/extcmd.c
index c236be13a..7f8cb3f67 100644
--- a/grub-core/commands/extcmd.c
+++ b/grub-core/commands/extcmd.c
@@ -139,6 +139,9 @@ grub_register_extcmd_lockdown (const char *name, grub_extcmd_func_t func,
 void
 grub_unregister_extcmd (grub_extcmd_t ext)
 {
+  if (ext == NULL)
+    return;
+
   grub_unregister_command (ext->cmd);
   grub_free (ext);
 }
diff --git a/grub-core/kern/command.c b/grub-core/kern/command.c
index 5812e131c..a1b4c81a9 100644
--- a/grub-core/kern/command.c
+++ b/grub-core/kern/command.c
@@ -104,6 +104,9 @@ grub_register_command_lockdown (const char *name,
 void
 grub_unregister_command (grub_command_t cmd)
 {
+  if (cmd == NULL)
+    return;
+
   if ((cmd->prio & GRUB_COMMAND_FLAG_ACTIVE) && (cmd->next))
     cmd->next->prio |= GRUB_COMMAND_FLAG_ACTIVE;
   grub_list_remove (GRUB_AS_LIST (cmd));
-- 
2.51.0


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