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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,
        syzbot+cd8bcd40cb049efa2770@syzkaller.appspotmail.com,
        "Laura Abbott" <labbott@redhat.com>,
        "syzbot" <syzkaller@googlegroups.com>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.789319473@decadent.org.uk>
Subject: [PATCH 3.16 054/366] staging: android: ion: Switch to
 pr_warn_once in ion_buffer_destroy
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

From: Laura Abbott <labbott@redhat.com>

commit 45ad559a29629cb1c64ee636563c69b71524f077 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/staging/android/ion/ion.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -272,8 +272,11 @@ err2:
 
 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->unmap_dma(buffer->heap, buffer);
 	buffer->heap->ops->free(buffer);
 	if (buffer->pages)