[SECURITY] xfs: fix ATTR_REPLACE shortform->longform xattr conversion failure (CVE-2018-18690)#126
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Fix CVE-2018-18690.
Upstream commit: 7b38460dc8e4eafba06c78f8e37099d3b34d473c
XFS could be forced into a filesystem shutdown by a local user able to set
attributes, by triggering an unchecked error condition during an xattr change.
Specifically, when expanding a small xattr (shortform) into a larger xattr
(longform) with ATTR_REPLACE, the old attr is removed but ATTR_REPLACE was
not cleared before re-adding after conversion, causing the add path to fail
and leading to a filesystem shutdown / non-operational state.
This patch checks the remove return value and clears ATTR_REPLACE after
removing the old attr to avoid the failure during conversion.
Reference: CVE-2018-18690