From 545ea44ea986a3e91bb2561dcc5181011f327d0a Mon Sep 17 00:00:00 2001 From: Todd Kjos Date: Tue, 12 Oct 2021 09:56:12 -0700 Subject: [PATCH] binder: use euid from cred instead of using task 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. Mot-CRs-fixed: (CR) CVE-Fixed: CVE-2021-39686 Bug: 200688826 Change-Id: Ia308ffe189b5e6f740c310d4d9d5e39451fcaed4 Cc: stable@vger.kernel.org # 4.4+ Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") Signed-off-by: Todd Kjos Suggested-by: Stephen Smalley Suggested-by: Jann Horn Acked-by: Casey Schaufler Signed-off-by: Paul Moore Signed-off-by: Greg Kroah-Hartman Signed-off-by: Gajjala Chakradhar Reviewed-on: https://gerrit.mot.com/2197695 SME-Granted: SME Approvals Granted SLTApproved: Slta Waiver Tested-by: Jira Key Reviewed-by: Xiangpo Zhao Submit-Approved: Jira Key --- drivers/android/binder.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index d273f2c11403..a33f509f122e 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -505,6 +505,9 @@ struct binder_priority { * @files files_struct for process * (protected by @files_lock) * @files_lock mutex to protect @files + * @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 @@ -551,6 +554,7 @@ struct binder_proc { struct task_struct *tsk; struct files_struct *files; struct mutex files_lock; + const struct cred *cred; struct hlist_node deferred_work_node; int deferred_work; bool is_dead; @@ -3204,7 +3208,7 @@ static void binder_transaction(struct binder_proc *proc, 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; @@ -4662,6 +4666,7 @@ static void binder_free_proc(struct binder_proc *proc) BUG_ON(!list_empty(&proc->delivered_death)); binder_alloc_deferred_release(&proc->alloc); put_task_struct(proc->tsk); + put_cred(proc->cred); binder_stats_deleted(BINDER_STAT_PROC); kfree(proc); } @@ -5138,6 +5143,7 @@ static int binder_open(struct inode *nodp, struct file *filp) get_task_struct(current->group_leader); proc->tsk = current->group_leader; mutex_init(&proc->files_lock); + proc->cred = get_cred(filp->f_cred); INIT_LIST_HEAD(&proc->todo); if (binder_supported_policy(current->policy)) { proc->default_priority.sched_policy = current->policy; -- 2.20.1