MFC O_SEARCH: r357412, r357461, r357580, r357584, r357636, r357671, r357688

MFC O_SEARCH: r357412, r357461, r357580, r357584, r357636, r357671, r357688

r357412:
Provide O_SEARCH

O_SEARCH is defined by POSIX [0] to open a directory for searching, skipping
permissions checks on the directory itself after the initial open(). This is
close to the semantics we've historically applied for O_EXEC on a directory,
which is UB according to POSIX. Conveniently, O_SEARCH on a file is also
explicitly undefined behavior according to POSIX, so O_EXEC would be a fine
choice. The spec goes on to state that O_SEARCH and O_EXEC need not be
distinct values, but they're not defined to be the same value.

This was pointed out as an incompatibility with other systems that had made
its way into libarchive, which had assumed that O_EXEC was an alias for
O_SEARCH.

This defines compatibility O_SEARCH/FSEARCH (equivalent to O_EXEC and FEXEC
respectively) and expands our UB for O_EXEC on a directory. O_EXEC on a
directory is checked in vn_open_vnode already, so for completeness we add a
NOEXECCHECK when O_SEARCH has been specified on the top-level fd and do not
re-check that when descending in namei.

[0] https://pubs.opengroup.org/onlinepubs/9699919799/

r357461:
namei: preserve errors from fget_cap_locked

Most notably, we want to make sure we don't clobber any capabilities-related
errors. This is a regression from r357412 (O_SEARCH) that was picked up by
the capsicum tests.

r357580:
O_SEARCH test: drop O_SEARCH|O_RDWR local diff

In FreeBSD's O_SEARCH implementation, O_SEARCH in conjunction with O_RDWR or
O_WRONLY is explicitly rejected. In this case, O_RDWR was not necessary
anyways as the file will get created with or without it.

This was submitted upstream as misc/54940 and committed in rev 1.8 of the
file.

r357584:
Record-only MFV of r357583: netbsd-tests: import upstreamed changes

The changes in question originated in FreeBSD/head; no further action is
required.

r357636:
MFV r357635: imnport v1.9 of the O_SEARCH tests

The RCSID data was wrong, so this is effectively a record-only merge
with correction of said data. No further changes should be needed in this
area, as we've now upstreamed our local changes to this specific test.

r357671:
O_SEARCH test: mark revokex an expected fail on NFS

The revokex test does not work when the scratch directory is created on NFS.
Given the nature of NFS, it likely can never work without looking like a
security hole since O_SEARCH would rely on the server knowing that the
directory did have +x at the time of open and that it's OK for it to have
been revoked based on POSIX specification for O_SEARCH.

This does mean that O_SEARCH is only partially functional on NFS in general,
but I suspect the execute bit getting revoked in the process is likely not
common.

r357688:
MFV r357687: Import NFS fix for O_SEARCH tests

The version that ended upstream was ultimately slightly different than the
version committed here; notably, statvfs() is used but it's redefined
appropriately to statfs() on FreeBSD since we don't provide the fstypename
for the former interface.