[PATCH] soc: qcom: cmd-db: Fix probe race with possible ERR_PTR dereference

[Krzysztof Kozlowski]

cmd_db_dev_probe() stores the result of devm_memremap() directly in the
global "cmd_db_header" variable and only afterwards validates it, which
opens a very short window where a concurrent thread could access and
dereference stored ERR_PTR.

Theoretical (not reproduced) race condition could look like:

  CPU 0                               CPU 1
  -----                               -----
  cmd_db_dev_probe()
    cmd_db_header = devm_memremap();
    // holds ERR_PTR
                                      cmd_db_ready()
                                        if (cmd_db_header == NULL)
                                          // false, proceeds
                                        cmd_db_magic_matches(cmd_db_header);
                                          // oops on ERR_PTR
    if (IS_ERR(cmd_db_header))
      cmd_db_header = NULL;

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: https://sashiko.dev/#/bug/linux-1e6d9e1c-b97d-447c-9cbc-d874a0609918
Fixes: 0da7824734d8 ("soc: qcom: cmd-db: Use devm_memremap() to fix memory leak in cmd_db_dev_probe")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>
---
 drivers/soc/qcom/cmd-db.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index 3f1eee784387..5d303ca0dbd0 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -340,8 +340,8 @@ static const struct file_operations cmd_db_debugfs_ops = {
 
 static int cmd_db_dev_probe(struct platform_device *pdev)
 {
+	struct cmd_db_header *header;
 	struct reserved_mem *rmem;
-	int ret = 0;
 
 	rmem = of_reserved_mem_lookup(pdev->dev.of_node);
 	if (!rmem) {
@@ -349,19 +349,17 @@ static int cmd_db_dev_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	cmd_db_header = devm_memremap(&pdev->dev, rmem->base, rmem->size, MEMREMAP_WC);
-	if (IS_ERR(cmd_db_header)) {
-		ret = PTR_ERR(cmd_db_header);
-		cmd_db_header = NULL;
-		return ret;
-	}
+	header = devm_memremap(&pdev->dev, rmem->base, rmem->size, MEMREMAP_WC);
+	if (IS_ERR(header))
+		return PTR_ERR(header);
 
-	if (!cmd_db_magic_matches(cmd_db_header)) {
+	if (!cmd_db_magic_matches(header)) {
 		dev_err(&pdev->dev, "Invalid Command DB Magic\n");
-		cmd_db_header = NULL;
 		return -EINVAL;
 	}
 
+	cmd_db_header = header;
+
 	debugfs_create_file("cmd-db", 0400, NULL, NULL, &cmd_db_debugfs_ops);
 
 	device_set_pm_not_required(&pdev->dev);
-- 
2.53.0