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binder: use euid from cred instead of using task

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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@vger.kernel.org # 4.4+
Fixes: 457b9a6f09f0 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Todd Kjos 2021-10-12 09:56:12 -07:00 committed by Greg Kroah-Hartman
parent ab95ef83dd
commit 443fc43d2f
1 changed files with 4 additions and 1 deletions
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5
drivers/android/binder.c
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@ -303,6 +303,7 @@ 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;
void *buffer;
@ -1505,7 +1506,7 @@ 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;
@ -3036,6 +3037,7 @@ 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);
init_waitqueue_head(&proc->wait);
proc->default_priority = task_nice(current);
@ -3241,6 +3243,7 @@ static void binder_deferred_release(struct binder_proc *proc)
}
put_task_struct(proc->tsk);
put_cred(proc->cred);
binder_debug(BINDER_DEBUG_OPEN_CLOSE,
"%s: %d threads %d, nodes %d (ref %d), refs %d, active transactions %d, buffers %d, pages %d\n",