This is a note to let you know that I've just added the patch titled binder: use euid from cred instead of using task to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: binder-use-euid-from-cred-instead-of-using-task.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 29bc22ac5e5bc63275e850f0c8fc549e3d0e306b Mon Sep 17 00:00:00 2001 From: Todd Kjos <tkjos@xxxxxxxxxx> Date: Tue, 12 Oct 2021 09:56:12 -0700 Subject: binder: use euid from cred instead of using task From: Todd Kjos <tkjos@xxxxxxxxxx> commit 29bc22ac5e5bc63275e850f0c8fc549e3d0e306b upstream. Save the 'struct cred' associated with a binder process at initial open to avoid potential race conditions when converting to an euid. Set a transaction's sender_euid from the 'struct cred' saved at binder_open() instead of looking up the euid from the binder proc's 'struct task'. This ensures the euid is associated with the security context that of the task that opened binder. Cc: stable@xxxxxxxxxxxxxxx # 4.4+ Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx> Suggested-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx> Suggested-by: Jann Horn <jannh@xxxxxxxxxx> Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/android/binder.c | 4 +++- drivers/android/binder_internal.h | 4 ++++ 2 files changed, 7 insertions(+), 1 deletion(-) --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2711,7 +2711,7 @@ static void binder_transaction(struct bi t->from = thread; else t->from = NULL; - t->sender_euid = task_euid(proc->tsk); + t->sender_euid = proc->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; @@ -4353,6 +4353,7 @@ static void binder_free_proc(struct bind } binder_alloc_deferred_release(&proc->alloc); put_task_struct(proc->tsk); + put_cred(proc->cred); binder_stats_deleted(BINDER_STAT_PROC); kfree(proc); } @@ -5055,6 +5056,7 @@ static int binder_open(struct inode *nod spin_lock_init(&proc->outer_lock); get_task_struct(current->group_leader); proc->tsk = current->group_leader; + proc->cred = get_cred(filp->f_cred); INIT_LIST_HEAD(&proc->todo); init_waitqueue_head(&proc->freeze_wait); proc->default_priority = task_nice(current); --- a/drivers/android/binder_internal.h +++ b/drivers/android/binder_internal.h @@ -364,6 +364,9 @@ struct binder_ref { * (invariant after initialized) * @tsk task_struct for group_leader of process * (invariant after initialized) + * @cred struct cred associated with the `struct file` + * in binder_open() + * (invariant after initialized) * @deferred_work_node: element for binder_deferred_list * (protected by binder_deferred_lock) * @deferred_work: bitmap of deferred work to perform @@ -426,6 +429,7 @@ struct binder_proc { struct list_head waiting_threads; int pid; struct task_struct *tsk; + const struct cred *cred; struct hlist_node deferred_work_node; int deferred_work; int outstanding_txns; Patches currently in stable-queue which might be from tkjos@xxxxxxxxxx are queue-5.14/binder-use-cred-instead-of-task-for-selinux-checks.patch queue-5.14/binder-don-t-detect-sender-target-during-buffer-cleanup.patch queue-5.14/binder-use-cred-instead-of-task-for-getsecid.patch queue-5.14/binder-use-euid-from-cred-instead-of-using-task.patch