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ufs: Avoid subobject overflow in snapshot expunge code

Authored by jrtc27 on Dec 24 2021, 4:08 PM.



The code here tries to be smart and zeroes out both di_db and di_ib with
a single bzero call, thereby overrunning the di_db subobject. This is
fine on most architectures, if a little dodgy. However, on CHERI, the
compiler can optionally restrict the bounds on pointers to subobjects to
just that subobject, in order to mitigate intra-object buffer overflows,
and this is enabled in CheriBSD's pure-capability kernels.

Instead, use separate bzero calls for each array, and let the compiler
optimise it as it sees fit; even if it's not generating inline zeroing
code, Clang will happily optimise two consecutive bzero's to a single
larger call.

Diff Detail

R10 FreeBSD src repository
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.