kvm: properly check debugfs dentry before using it

gregkh · torvalds · commit 8ed0579c12b2 · 2019-02-28T08:57:32.000-08:00
debugfs can now report an error code if something went wrong instead of just NULL. So if the return value is to be used as a "real" dentry, it needs to be checked if it is an error before dereferencing it. This is now happening because of ff9fb72 ("debugfs: return error values, not NULL"). syzbot has found a way to trigger multiple debugfs files attempting to be created, which fails, and then the error code gets passed to dentry_path_raw() which obviously does not like it. Reported-by: Eric Biggers <ebiggers@kernel.org> Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com Cc: "Radim Krčmář" <rkrcmar@redhat.com> Cc: kvm@vger.kernel.org Acked-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
 	}
 	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
 
-	if (kvm->debugfs_dentry) {
+	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
 		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
 
 		if (p) {

Original file line number	Diff line number	Diff line change
`@@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)`
`4044`	`4044`	`}`
`4045`	`4045`	`add_uevent_var(env, "PID=%d", kvm->userspace_pid);`
`4046`	`4046`
`4047`		`- if (kvm->debugfs_dentry) {`
	`4047`	`+ if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {`
`4048`	`4048`	`char tmp, p = kmalloc(PATH_MAX, GFP_KERNEL);`
`4049`	`4049`
`4050`	`4050`	`if (p) {`