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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Darren Kenny <darren.kenny@oracle.com>
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Date: Tue, 24 Nov 2020 16:41:49 +0000
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Subject: [PATCH] zfs: Fix possible negative shift operation
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While it is possible for the return value from zfs_log2() to be zero
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(0), it is quite unlikely, given that the previous assignment to blksz
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is shifted up by SPA_MINBLOCKSHIFT (9) before 9 is subtracted at the
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assignment to epbs.
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But, while unlikely during a normal operation, it may be that a carefully
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crafted ZFS filesystem could result in a zero (0) value to the
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dn_datalbkszsec field, which means that the shift left does nothing
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and assigns zero (0) to blksz, resulting in a negative epbs value.
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Fixes: CID 73608
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Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/fs/zfs/zfs.c | 5 +++++
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1 file changed, 5 insertions(+)
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diff --git a/grub-core/fs/zfs/zfs.c b/grub-core/fs/zfs/zfs.c
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index c6204367e..3dfde0807 100644
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--- a/grub-core/fs/zfs/zfs.c
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+++ b/grub-core/fs/zfs/zfs.c
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@@ -2667,6 +2667,11 @@ dnode_get (dnode_end_t * mdn, grub_uint64_t objnum, grub_uint8_t type,
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blksz = grub_zfs_to_cpu16 (mdn->dn.dn_datablkszsec,
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mdn->endian) << SPA_MINBLOCKSHIFT;
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epbs = zfs_log2 (blksz) - DNODE_SHIFT;
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+
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+ /* While this should never happen, we should check that epbs is not negative. */
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+ if (epbs < 0)
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+ epbs = 0;
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+
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blkid = objnum >> epbs;
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idx = objnum & ((1 << epbs) - 1);
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