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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "Eric Biggers" <ebiggers@google.com>,
        "syzbot" <syzkaller@googlegroups.com>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.752807048@decadent.org.uk>
Subject: [PATCH 3.16 246/410] binder: check for binder_thread allocation
 failure in binder_poll()
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit f88982679f54f75daa5b8eff3da72508f1e7422f upstream.

If the kzalloc() in binder_get_thread() fails, binder_poll()
dereferences the resulting NULL pointer.

Fix it by returning POLLERR if the memory allocation failed.

This bug was found by syzkaller using fault injection.

Reported-by: syzbot <syzkaller@googlegroups.com>
Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16:
 - Drop the binder global lock before returning
 - Adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/staging/android/binder.c
+++ b/drivers/staging/android/binder.c
@@ -2572,6 +2572,10 @@ static unsigned int binder_poll(struct f
 	binder_lock(__func__);
 
 	thread = binder_get_thread(proc);
+	if (!thread) {
+		binder_unlock(__func__);
+		return POLLERR;
+	}
 
 	wait_for_proc_work = thread->transaction_stack == NULL &&
 		list_empty(&thread->todo) && thread->return_error == BR_OK;