grub: add a fix for a possible negative shift

This patch adds a fix for a possible negative shift in grub's zfs.
It is a part of a security series [1].

[1] https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00007.html

(From OE-Core rev: d5a93d55b5f3bfd890aa2925869d2a5ba4299801)

Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-bsp/grub/files/0021-zfs-Fix-possible-negative-shift-operation.patch

@@ -0,0 +1,42 @@
+From c757779e5d09719666c3b155afd2421978a107bd Mon Sep 17 00:00:00 2001
+From: Darren Kenny <darren.kenny@oracle.com>
+Date: Tue, 24 Nov 2020 16:41:49 +0000
+Subject: [PATCH] zfs: Fix possible negative shift operation
+
+While it is possible for the return value from zfs_log2() to be zero
+(0), it is quite unlikely, given that the previous assignment to blksz
+is shifted up by SPA_MINBLOCKSHIFT (9) before 9 is subtracted at the
+assignment to epbs.
+
+But, while unlikely during a normal operation, it may be that a carefully
+crafted ZFS filesystem could result in a zero (0) value to the
+dn_datalbkszsec field, which means that the shift left does nothing
+and assigns zero (0) to blksz, resulting in a negative epbs value.
+
+Fixes: CID 73608
+
+Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
+Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
+
+Upstream-Status: Backport [https://git.savannah.gnu.org/cgit/grub.git/commit/?id=a02091834d3e167320d8a262ff04b8e83c5e616d]
+Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
+---
+ grub-core/fs/zfs/zfs.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/grub-core/fs/zfs/zfs.c b/grub-core/fs/zfs/zfs.c
+index 36d0373..0c42cba 100644
+--- a/grub-core/fs/zfs/zfs.c
++++ b/grub-core/fs/zfs/zfs.c
+@@ -2667,6 +2667,11 @@ dnode_get (dnode_end_t * mdn, grub_uint64_t objnum, grub_uint8_t type,
+   blksz = grub_zfs_to_cpu16 (mdn->dn.dn_datablkszsec, 
+ 			     mdn->endian) << SPA_MINBLOCKSHIFT;
+   epbs = zfs_log2 (blksz) - DNODE_SHIFT;
++
++  /* While this should never happen, we should check that epbs is not negative. */
++  if (epbs < 0)
++    epbs = 0;
++
+   blkid = objnum >> epbs;
+   idx = objnum & ((1 << epbs) - 1);
+ 

meta/recipes-bsp/grub/grub2.inc

@@ -67,6 +67,7 @@ SRC_URI = "${GNU_MIRROR}/grub/grub-${PV}.tar.gz \
            file://0018-disk-ldm-Fix-memory-leak-on-uninserted-lv-references.patch \
            file://0019-disk-cryptodisk-Fix-potential-integer-overflow.patch \
            file://0020-hfsplus-Check-that-the-volume-name-length-is-valid.patch \
+           file://0021-zfs-Fix-possible-negative-shift-operation.patch \
            "
 SRC_URI[md5sum] = "5ce674ca6b2612d8939b9e6abed32934"
 SRC_URI[sha256sum] = "f10c85ae3e204dbaec39ae22fa3c5e99f0665417e91c2cb49b7e5031658ba6ea"