staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy

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>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 83dc3292e9ab1dd2fef1e85d898448cba7444c11..24cb666c922428b3fe33ce174115d009d2f2f100 100644 (file)
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -131,8 +131,11 @@ 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->free(buffer);
        kfree(buffer);
 }