[ 78/78] cred: copy_process() should clear child->replacement_session_keyring

[Greg KH]

3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@xxxxxxxxxx>

commit 79549c6dfda0603dba9a70a53467ce62d9335c33 upstream.

keyctl_session_to_parent(task) sets ->replacement_session_keyring,
it should be processed and cleared by key_replace_session_keyring().

However, this task can fork before it notices TIF_NOTIFY_RESUME and
the new child gets the bogus ->replacement_session_keyring copied by
dup_task_struct(). This is obviously wrong and, if nothing else, this
leads to put_cred(already_freed_cred).

change copy_creds() to clear this member. If copy_process() fails
before this point the wrong ->replacement_session_keyring doesn't
matter, exit_creds() won't be called.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/cred.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -385,6 +385,8 @@ int copy_creds(struct task_struct *p, un
 	struct cred *new;
 	int ret;
 
+	p->replacement_session_keyring = NULL;
+
 	if (
 #ifdef CONFIG_KEYS
 		!p->cred->thread_keyring &&


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