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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);
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