MFC r363435:

Avoid reading one byte before the path buffer.

This happens when there's only one component (e.g. "/foo"). This
(mostly-harmless) bug has been present since June 1990 when it was
commited to mountd.c SCCS version 5.9.

Note: the bug is on the second changed line, the first line is changed
for visual consistency.

Reviewed by: cem, emaste, mckusick, rmacklem
Reported by: CHERI
Obtained from: CheriBSD
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D25759

MFC r363439:

Correct a type-mismatch between xdr_long and the variable "bad".

Way back in r28911 (August 1997, CVS rev 1.22) we imported a NetBSD
information leak fix via OpenBSD. Unfortunatly we failed to track the
followup commit that fixed the type of the error code. Apply the change
from int to long now.

Reviewed by: emaste
Reported by: CHERI
Obtained from: CheriBSD
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D25779

MFC: r361854
Fix mountd so that it will not lose SIGHUPs that indicate "reload exports".

Without this patch, if a SIGHUP is handled while the process is executing
get_exportlist(), that SIGHUP is essentially ignored because the got_sighup
variable is reset to 0 after get_exportlist().
This results in the exports file(s) not being reloaded until another SIGHUP
signal is sent to mountd.
This patch fixes this by resetting got_sighup to zero before the
get_exportlist() call while SIGHUP is blocked.
It also defines a delay time of 250msec before doing another exports reload
if there are RPC request(s) to process. This prevents repeated exports reloads
from delaying handling of RPC requests significantly.

PR: 246597

MFC: r361780, r361956
Fix mountd to handle getgrouplist() not returning groups[0] == groups[1].

Prior to r174547, getgrouplist(3) always returned a groups list with
element 0 and 1 set to the basegid argument, so long as ngroups was > 1.
Post-r174547 this is not the case. r328304 disabled the deduplication that
removed the duplicate, but the duplicate still does not occur unless the
group for a user in the password database is also entered in the group
database.
This patch fixes mountd so that it handles the case where a user specified
with the -maproot or -mapall exports option has a getgrouplist(3) groups
list where groups[0] != groups[1].

MFC: r348590, r348591
Modify mountd so that it incrementally updates the kernel exports upon a reload.

Without this patch, mountd would delete/load all exports from the exports
file(s) when it receives a SIGHUP. This works fine for small exports file(s),
but can take several seconds to do when there are large numbers (10000+) of
exported file systems. Most of this time is spent doing the system calls
that delete/export each of these file systems. When the "-S" option
has been specified (the default these days), the nfsd threads are suspended
for several seconds while the reload is done.

This patch changes mountd so that it only does system calls for file systems
where the exports have been changed/added/deleted as compared to the exports
done for the previous load/reload of the exports file(s).
Basically, when SIGHUP is posted to mountd, it saves the exportlist structures
from the previous load and creates a new set of structures from the current
exports file(s). Then it compares the current with the previous and only does
system calls for cases that have been changed/added/deleted.
The nfsd threads do not need to be suspended until the comparison step is
being done. This results in a suspension period of milliseconds for a server
with 10000+ exported file systems.

There is some code using a LOGDEBUG() macro that allow runtime debugging
output via syslog(LOG_DEBUG,...) that can be enabled by creating a file
called /var/log/mountd.debug. This code is expected to be replaced with
code that uses dtrace by cy@ in the near future, once issues w.r.t. dtrace
in stable/12 have been resolved.

The patch should not change the usage of the exports file(s), but improves
the performance of reloading large exports file(s) where there are only a
small number of changes done to the file(s).

PR: 237860

MFC: r348452
Replace a single linked list with a hash table of lists.

mountd.c uses a single linked list of "struct exportlist" structures,
where there is one of these for each exported file system on the NFS server.
This list gets long if there are a large number of file systems exported and
the list must be searched for each line in the exports file(s) when
SIGHUP causes the exports file(s) to be reloaded.
A simple benchmark that traverses SLIST() elements and compares two 32bit
fields in the structure for equal (which is what the search is)
appears to take a couple of nsec. So, for a server with 72000 exported file
systems, this can take about 5sec during reload of the exports file(s).
By replacing the single linked list with a hash table with a target of
10 elements per list, the time should be reduced to less than 1msec.
Peter Errikson (who has a server with 72000+ exported file systems) ran
a test program using 5 hashes to see how they worked.
fnv_32_buf(fsid,..., 0)
fnv_32_buf(fsid,..., FNV1_32_INIT)
hash32_buf(fsid,..., 0)
hash32_buf(fsid,..., HASHINIT)
- plus simply using the low order bits of fsid.val[0].
The first three behaved about equally well, with the first one being
slightly better than the others.
It has an average variation of about 4.5% about the target list length
and that is what this patch uses.
Peter Errikson also tested this hash table version and found that the
performance wasn't measurably improved by a larger hash table, so a
load factor of 10 appears adequate.

PR: 237860

MFC r349376: Fix strsep_quote() on strings without quotes.

For strings without quotes and escapes dstptr and srcptr are equal, so
zeroing *dstptr before checking *srcptr is not a good idea. In practice
it means that in -maproot=65534:65533 everything after the colon is lost.

The problem was there since r293305, but before r346976 it was covered by
improper strsep_quote() usage.

PR: 238725

MFC: r347583
Replace global list for grouplist with list(s) for each exportlist element.

In mountd.c, the grouplist structures are linked into a single global
linked list headed by "grphead". The only use of this linked list is
to free all list elements when the exportlist elements are also all being
free'd at the time the exports are being reloaded.
This patch replaces this one global linked list head with a list head in
each exportlist structure, where the grouplist elements for that exported
file system are linked.
The only change is that now the grouplist elements are free'd with the
associated exportlist element as they are free'd instead of all grouplist
elements being free'd after the exportlist elements are free'd. This
change should have no effect in practice.
This is being done, since a future patch that will add a "-I" option for
incrementally updating the exports in the kernel needs to know which
grouplist elements are associated with each exported file system and
having them linked into a list headed by the exportlist element does that.

PR: 237860

MFC: r347498
Factor code into two new functions in preparation for a future commit.

Factor code into two functions.
read_exportfile() a functon which reads the exports file(s) and calls
get_exportlist_one() to process each of them.
delete_export() a function which deletes the exports in the kernel for a file
system.
The contents of these functions is just the same code as was used to do the
operations, moved into separate functions. As such, there is no semantic change.
This is being done in preparation for a future commit that will add an
option to do incremental changes of kernel exports upon receiving SIGHUP.

PR: 237860

MFC: r347476
Factor out some exportlist list operations into separate functions.

This patch moves the code that removes and frees all exportlist elements
out into a separate function called free_exports().
It does the same for the insertion of a new exportlist entry into a list.
It also adds a second argument to ex_search() for the list to use.
None of these changes have any semantic effect. They are being done to
prepare the code for future patches that convert the single linked list
for the exportlist to a hash table of lists and a patch that will do
incremental changes of exports in the kernel.
And it fixes the argument for SLIST_HEAD_INITIALIZER() to a pointer,
which doesn't really matter, since SLIST_HEAD_INITIALIZER() doesn't use
the argument.

PR: 237860

MFC r346976: Respect quotes and escapes when splitting exports fields.

Without this r293305 was still unable to handle names with spaces.

MFC r341641 (by sef): Reduce number of DNS queries in mountd.

MFC r340442

mountd has no way to configure the listen queue depth; rather than add a new
option, we pass -1 down to listen, which causes it to use the
kern.ipc.soacceptqueue sysctl.

Approved by: mav
Sponsored by: iXsystems Inc

MFC r332559: mountd: fix a crash when getgrouplist reports too many groups

Sponsored by: Panzura

Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)