[PATCH 3.16 054/366] staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy

Ben Hutchings
2018-11-11T20:07:12Z

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)