From: Jann Horn jannh@google.com
commit 6994eefb0053799d2e07cd140df6c2ea106c41ee upstream.
Fix two issues:
When called for PTRACE_TRACEME, ptrace_link() would obtain an RCU reference to the parent's objective credentials, then give that pointer to get_cred(). However, the object lifetime rules for things like struct cred do not permit unconditionally turning an RCU reference into a stable reference.
PTRACE_TRACEME records the parent's credentials as if the parent was acting as the subject, but that's not the case. If a malicious unprivileged child uses PTRACE_TRACEME and the parent is privileged, and at a later point, the parent process becomes attacker-controlled (because it drops privileges and calls execve()), the attacker ends up with control over two processes with a privileged ptrace relationship, which can be abused to ptrace a suid binary and obtain root privileges.
Fix both of these by always recording the credentials of the process that is requesting the creation of the ptrace relationship: current_cred() can't change under us, and current is the proper subject for access control.
This change is theoretically userspace-visible, but I am not aware of any code that it will actually break.
Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP") Signed-off-by: Jann Horn jannh@google.com Acked-by: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/ptrace.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -74,9 +74,7 @@ void __ptrace_link(struct task_struct *c */ static void ptrace_link(struct task_struct *child, struct task_struct *new_parent) { - rcu_read_lock(); - __ptrace_link(child, new_parent, __task_cred(new_parent)); - rcu_read_unlock(); + __ptrace_link(child, new_parent, current_cred()); }
/**