patch "staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy" added to staging-testing

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the staging-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


>From 45ad559a29629cb1c64ee636563c69b71524f077 Mon Sep 17 00:00:00 2001
From: Laura Abbott <labbott@redhat.com>
Date: Mon, 14 May 2018 14:35:09 -0700
Subject: staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy

Syzbot reported yet another warning with Ion:

WARNING: CPU: 0 PID: 1467 at drivers/staging/android/ion/ion.c:122
ion_buffer_destroy+0xd4/0x190 drivers/staging/android/ion/ion.c:122
Kernel panic - not syncing: panic_on_warn set ...

This is catching that a buffer was freed with an existing kernel mapping
still present. This can be easily be triggered from userspace by calling
DMA_BUF_SYNC_START without calling DMA_BUF_SYNC_END. Switch to a single
pr_warn_once to indicate the error without being disruptive.

Reported-by: syzbot+cd8bcd40cb049efa2770@syzkaller.appspotmail.com
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/staging/android/ion/ion.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index af682cbde767..9d1109e43ed4 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -111,8 +111,11 @@ static struct ion_buffer *ion_buffer_create(struct ion_heap *heap,
 
 void ion_buffer_destroy(struct ion_buffer *buffer)
 {
-	if (WARN_ON(buffer->kmap_cnt > 0))
+	if (buffer->kmap_cnt > 0) {
+		pr_warn_once("%s: buffer still mapped in the kernel\n",
+			     __func__);
 		buffer->heap->ops->unmap_kernel(buffer->heap, buffer);
+	}
 	buffer->heap->ops->free(buffer);
 	kfree(buffer);
 }
-- 
2.17.0