[openwrt/openwrt] base-files: fix sysupgrade for kernel-out-of-UBI

[LEDE Commits]

dangole pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/7d02fc0951ffcff3ba885374b108d20de92eddbe

commit 7d02fc0951ffcff3ba885374b108d20de92eddbe
Author: Rodrigo Balerdi <lanchon at gmail.com>
AuthorDate: Mon May 2 05:33:01 2022 -0300

    base-files: fix sysupgrade for kernel-out-of-UBI
    
    Commit ecbcc0b59551 bricks devices on which the raw kernel and UBI mtd
    partitions overlap.
    
    This is the case of the ZyXEL NR7101 for example. Its OEM bootloader has
    no UBI support. OpenWrt splits the stock kernel mtd partition into a raw
    kernel part used by the bootloader and a UBI part used to store rootfs
    and rootfs_data. Running mtd erase on the complete partition during
    sysupgrade erases the UBI part and results in a soft brick.
    
    Arguably the best solution would be to fix the partition layouts so that
    kernel and UBI partitions do not overlap, also including a stock_kernel
    partition to help reverting to stock firmware. This would have the added
    benefit of protecting UBI from kernel images that are excessively large.
    
    Fixes: ecbcc0b59551 ("base-files: safer sysupgrade.tar for kernel-out-of-UBI")
    Reported-by: Bjørn Mork <bjorn at mork.no>
    Signed-off-by: Rodrigo Balerdi <lanchon at gmail.com>
---
 package/base-files/files/lib/upgrade/nand.sh | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/package/base-files/files/lib/upgrade/nand.sh b/package/base-files/files/lib/upgrade/nand.sh
index 5ecdb0ff23..c9960bf9d4 100644
--- a/package/base-files/files/lib/upgrade/nand.sh
+++ b/package/base-files/files/lib/upgrade/nand.sh
@@ -305,7 +305,11 @@ nand_upgrade_tar() {
 	local ubi_kernel_length
 	if [ "$kernel_length" ]; then
 		if [ "$kernel_mtd" ]; then
-			mtd erase "$CI_KERNPART"
+			# On some devices, the raw kernel and ubi partitions overlap.
+			# These devices brick if the kernel partition is erased.
+			# Hence only invalidate kernel for now.
+			dd if=/dev/zero bs=4096 count=1 2>/dev/null | \
+				mtd write - "$CI_KERNPART"
 		else
 			ubi_kernel_length="$kernel_length"
 		fi
@@ -322,7 +326,7 @@ nand_upgrade_tar() {
 	if [ "$kernel_length" ]; then
 		if [ "$kernel_mtd" ]; then
 			tar xf "$tar_file" "$board_dir/kernel" -O | \
-				mtd -n write - "$CI_KERNPART"
+				mtd write - "$CI_KERNPART"
 		else
 			local kern_ubivol="$( nand_find_volume $ubidev "$CI_KERNPART" )"
 			tar xf "$tar_file" "$board_dir/kernel" -O | \