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    Subject[PATCH 4.17 09/45] staging: android: ion: Switch to pr_warn_once in ion_buffer_destroy
    Date
    4.17-stable 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>
    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(-)

    --- a/drivers/staging/android/ion/ion.c
    +++ b/drivers/staging/android/ion/ion.c
    @@ -114,8 +114,11 @@ 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);
    }

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