kernel/kcov: unproxify debugfs file's fops

Since commit 49d200deaa68 ("debugfs: prevent access to removed files'
private data"), a debugfs file's file_operations methods get proxied
through lifetime aware wrappers.

However, only a certain subset of the file_operations members is supported
by debugfs and ->mmap isn't among them -- it appears to be NULL from the
VFS layer's perspective.

This behaviour breaks the /sys/kernel/debug/kcov file introduced
concurrently with commit 5c9a8750a640 ("kernel: add kcov code coverage").

Since that file never gets removed, there is no file removal race and thus,
a lifetime checking proxy isn't needed.

Avoid the proxying for /sys/kernel/debug/kcov by creating it via
debugfs_create_file_unsafe() rather than debugfs_create_file().

Fixes: 49d200deaa68 ("debugfs: prevent access to removed files' private data")
Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/kcov.c b/kernel/kcov.c
index a02f2dd..8d44b3f 100644 (file)
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -264,7 +264,12 @@ static const struct file_operations kcov_fops = {
 
 static int __init kcov_init(void)
 {
-       if (!debugfs_create_file("kcov", 0600, NULL, NULL, &kcov_fops)) {
+       /*
+        * The kcov debugfs file won't ever get removed and thus,
+        * there is no need to protect it against removal races. The
+        * use of debugfs_create_file_unsafe() is actually safe here.
+        */
+       if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
                pr_err("failed to create kcov in debugfs\n");
                return -ENOMEM;
        }