Commit df4565f9 authored May 24, 2016 by Nicolai Stange Committed by Greg Kroah-Hartman Jun 15, 2016

kernel/kcov: unproxify debugfs file's fops



Since commit 49d200de ("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 5c9a8750 ("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: 49d200de ("debugfs: prevent access to removed files' private data")
Fixes: 5c9a8750 ("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>

parent 5edb5649

kernel/kcov.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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