fixes stack use after free detected by ASAN
2021-08-31T17:21:44.885938 [MAC-NR ] [D] [ 0] Building new MAC PDU (9 B)
==10908==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7ffc481b5340 at pc 0x563c0486d489 bp 0x7ffc481b4470 sp 0x7ffc481b4460
READ of size 1 at 0x7ffc481b5340 thread T0
#0 0x563c0486d488 in srsran::mac_sch_subpdu_nr::to_string(fmt::v7::basic_memory_buffer<char, 500ul, std::allocator<char> >&) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x139488)
#1 0x563c0486db87 in srsran::mac_sch_pdu_nr::to_string(fmt::v7::basic_memory_buffer<char, 500ul, std::allocator<char> >&) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x139b87)
#2 0x563c0481c127 in srsue::mux_nr::get_pdu(unsigned int) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0xe8127)
#3 0x563c0484e62b in srsue::ul_harq_entity_nr::ul_harq_process_nr::new_grant_ul(srsue::mac_interface_phy_nr::mac_nr_grant_ul_t const&, bool const&, srsue::mac_interface_phy_nr::tb_action_ul_t*) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x11a62b)
#4 0x563c04850de4 in srsue::ul_harq_entity_nr::new_grant_ul(srsue::mac_interface_phy_nr::mac_nr_grant_ul_t const&, srsue::mac_interface_phy_nr::tb_action_ul_t*) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x11cde4)
#5 0x563c047bb004 in srsue::mac_nr::new_grant_ul(unsigned int, srsue::mac_interface_phy_nr::mac_nr_grant_ul_t const&, srsue::mac_interface_phy_nr::tb_action_ul_t*) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x87004)
#6 0x563c04760cdc in msg3_test() (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x2ccdc)
#7 0x563c0475f762 in main (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x2b762)
#8 0x7fae1cf400b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
#9 0x563c047601bd in _start (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x2c1bd)
Address 0x7ffc481b5340 is located in stack of thread T0 at offset 320 in frame
#0 0x563c0486d78f in srsran::mac_sch_pdu_nr::to_string(fmt::v7::basic_memory_buffer<char, 500ul, std::allocator<char> >&) (/home/ubuntu/workspace/srslte_ubuntu_20.04_pull_request/srslte/build/srsue/src/stack/mac_nr/test/mac_nr_test+0x13978f)
setting the new PRACH params (writing the the local var) needs to protected as well
because it is called from the RRC context and the PHY worker will call configure_prach_params()
if it sees changes to it.
NAS states and substates maybe be requested from other threads so
they need to be protected.
Note that the caller still needs to hold it's own mutex if different
actions are required based on the state.