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.
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>
Cc: stable@xxxxxxxxxxxxxxx # 4.4+
---
v3: added this patch to series (as 3/3)
v5:
- combined with saving of 'struct cred' during binder_open()
- reordered to 1/1 as suggested by Stephen Smalley
drivers/android/binder.c | 4 +++-
drivers/android/binder_internal.h | 4 ++++
2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 9edacc8b9768..a396015e874a 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2711,7 +2711,7 @@ 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;
@@ -4353,6 +4353,7 @@ 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);
}
@@ -5055,6 +5056,7 @@ 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);
diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
index 402c4d4362a8..d6b6b8cb7346 100644
--- 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;
--
2.33.0.882.g93a45727a2-goog
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