[PATCH v6 08/16] printk: Ensure consistent name and devname when updating preferred console

[Petr Mladek <pmladek@suse.com>]

Make sure that add_or_update_preferred_console() updates the right entry.
It is a paranoid check which prevents a potential misuse of the API in
the future.

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2c205c454321..60923b997e4f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2564,6 +2564,8 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
  *
  *   2. Either @name and valid @idx OR @devname and @idx=-1 are allowed. [*]
  *
+ *   3. Only matching entries can be updated.
+ *
  *  [*] A valid @name and @idx will get assigned for a devname later when
  *	@devname matches during the device initialization, see
  *	match_devname_and_update_preferred_console().
@@ -2589,10 +2591,7 @@ static int add_or_update_preferred_console(unsigned int i,
 		return -EINVAL;
 	}
 
-	if (!pc->name[0] && !pc->devname[0])
-		is_new_entry = true;
-
-	if (is_new_entry && devname) {
+	if (devname) {
 		/*
 		 * A valid console name and index will get assigned when
 		 * a matching device gets registered.
@@ -2608,11 +2607,18 @@ static int add_or_update_preferred_console(unsigned int i,
 			return -EINVAL;
 		}
 
-		strscpy(pc->devname, devname);
-		pc->index = idx;
+		if (!pc->devname[0]) {
+			is_new_entry = true;
+			strscpy(pc->devname, devname);
+			pc->index = idx;
+		} else if (strcmp(pc->devname, devname) != 0) {
+			pr_err("Updating a preferred console with an invalid devname: %s vs. %s\n",
+			       pc->devname, devname);
+			return -EINVAL;
+		}
 	}
 
-	if (is_new_entry && name) {
+	if (name) {
 		/* A console name must be defined with a valid index. */
 		if (idx < 0) {
 			pr_err("Adding a preferred console with an invalid index: %s, %d\n",
@@ -2620,8 +2626,15 @@ static int add_or_update_preferred_console(unsigned int i,
 			return -EINVAL;
 		}
 
-		strscpy(pc->name, name);
-		pc->index = idx;
+		if (!pc->name[0]) {
+			is_new_entry = true;
+			strscpy(pc->name, name);
+			pc->index = idx;
+		} else if (strcmp(pc->name, name) != 0 || pc->index != idx) {
+			pr_err("Updating a preferred console with an invalid name or index: %s%d vs. %s%d\n",
+			       pc->name, pc->index, name, idx);
+			return -EINVAL;
+		}
 	}
 
 	/*
-- 
2.56.0