Patch "drm/mcde: dsi: Fix invalid pointer dereference if panel cannot be found" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    drm/mcde: dsi: Fix invalid pointer dereference if panel cannot be found

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-mcde-dsi-fix-invalid-pointer-dereference-if-pane.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b97a2a59f2db1b36b5804a182637a29ed74da180
Author: Stephan Gerhold <stephan@xxxxxxxxxxx>
Date:   Mon Nov 18 14:02:52 2019 +0100

    drm/mcde: dsi: Fix invalid pointer dereference if panel cannot be found
    
    [ Upstream commit c131280c03bd1c225c2e64e9ef75873ffca3d96e ]
    
    The "panel" pointer is not reset to NULL if of_drm_find_panel()
    returns an error. Therefore we later assume that a panel was found,
    and try to dereference the error pointer, resulting in:
    
        mcde-dsi a0351000.dsi: failed to find panel try bridge (4294966779)
        Unable to handle kernel paging request at virtual address fffffe03
        PC is at drm_panel_bridge_add.part.0+0x10/0x5c
        LR is at mcde_dsi_bind+0x120/0x464
        ...
    
    Reset "panel" to NULL to avoid this problem.
    Also change the format string of the error to %ld to print
    the negative errors correctly. The crash above then becomes:
    
        mcde-dsi a0351000.dsi: failed to find panel try bridge (-517)
        mcde-dsi a0351000.dsi: no panel or bridge
        ...
    
    Fixes: 5fc537bfd000 ("drm/mcde: Add new driver for ST-Ericsson MCDE")
    Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx>
    Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191118130252.170324-1-stephan@xxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
index f9c9e32b299c..35bb825d1918 100644
--- a/drivers/gpu/drm/mcde/mcde_dsi.c
+++ b/drivers/gpu/drm/mcde/mcde_dsi.c
@@ -935,11 +935,13 @@ static int mcde_dsi_bind(struct device *dev, struct device *master,
 	for_each_available_child_of_node(dev->of_node, child) {
 		panel = of_drm_find_panel(child);
 		if (IS_ERR(panel)) {
-			dev_err(dev, "failed to find panel try bridge (%lu)\n",
+			dev_err(dev, "failed to find panel try bridge (%ld)\n",
 				PTR_ERR(panel));
+			panel = NULL;
+
 			bridge = of_drm_find_bridge(child);
 			if (IS_ERR(bridge)) {
-				dev_err(dev, "failed to find bridge (%lu)\n",
+				dev_err(dev, "failed to find bridge (%ld)\n",
 					PTR_ERR(bridge));
 				return PTR_ERR(bridge);
 			}