linux-kernel - [PATCH] staging: android: ion: Switch to pr_warn_once in ion_buffer

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Date:   Mon, 14 May 2018 14:35:09 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Cc:     Laura Abbott <labbott@...hat.com>, devel@...verdev.osuosl.org,
        LKML <linux-kernel@...r.kernel.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>
Subject: [PATCH] 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@...kaller.appspotmail.com
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Laura Abbott <labbott@...hat.com>
---
 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 e74db7902549..a68329411b29 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -114,8 +114,11 @@ 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