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binder: use euid from cred instead of using task

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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@vger.kernel.org # 4.4+
Fixes: 457b9a6f09 ("Staging: android: add binder driver")
Signed-off-by: Todd Kjos <tkjos@google.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Suggested-by: Jann Horn <jannh@google.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Todd Kjos 2021-10-12 09:56:12 -07:00 committed by Paul Moore
parent 86dd9fd52e
commit 29bc22ac5e
2 changed files with 7 additions and 1 deletions
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4
drivers/android/binder.c
View File

@ -2702,7 +2702,7 @@ 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;
@ -4343,6 +4343,7 @@ static void binder_free_proc(struct binder_proc *proc)
}
binder_alloc_deferred_release(&proc->alloc);
put_task_struct(proc->tsk);
put_cred(proc->cred);
binder_stats_deleted(BINDER_STAT_PROC);
kfree(proc);
}
@ -5021,6 +5022,7 @@ static int binder_open(struct inode *nodp, struct file *filp)
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);

4
drivers/android/binder_internal.h
View File

@ -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
@ -424,6 +427,7 @@ 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;