As reported in https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=252157, on recent versions of FreeBSD 13.0-CURRENT with clang/llvm 11.0.0, the various samba ports (net/samba411, net/samba/412 and net/samba413) sometimes dump core when shares are accessed.

This turned out to be due to variable length arrays (VLAs) being used in source3/lib/messages.c, where sometimes the length would end up being zero, which is undefined behavior. For example, in messaging_recv_cb() there is a VLA 'fds64[]', being declared using incoming 'num_fds' parameter, which is sometimes zero, resulting in:

Program received signal SIGSEGV, Segmentation fault.
0x0000000801c784a7 in messaging_recv_cb (ev=0x805475060, msg=0x7fffffffdbe8 "\035#", msg_len=98, fds=0x7fffffffdbdc, num_fds=0, private_data=0x80546e300) at ../../source3/lib/messages.c:394
394             int64_t fds64[MIN(num_fds, INT8_MAX)];
(gdb) print num_fds
$6 = 0

To fix this, I propose to use MAX(1, number) to ensure the VLA is always declared with a length of at least 1. In the FreeBSD port case, this fixes the aforementioned core dumping occurrences.

I found two other places in source3/lib/messages.c using VLAs and incoming length parameters, which can also be fixed in the same way. The proposed fix is at:
https://gitlab.com/DimitryAndric/samba/-/commit/37b28febaaea58de08434eff7dcc73908b542ffd

I will also create a MR from this branch.