keychain.c crash when adding new keychain

[donaldsharp]

Description

Adding this config:

!
key chain mypass
 key 1
  cryptographic-algorithm hmac-sha-256
  key-string fsdfsdfsdfsdgsdg
 exit
exit

to frr.conf and then loading it with vtysh -b -n causes rip/ospf/pim/eigrp to crash with this stack trace:

(gdb) bt
#0  0x00007ffff7cd5198 in key_lookup (keychain=0x0, index=1) at lib/keychain.c:118
#1  0x00007ffff7cdc4d3 in key_chains_key_chain_key_crypto_algorithm_modify (args=0x7fffffff96f0) at lib/keychain_nb.c:551
#2  0x00007ffff7d0cfb4 in nb_callback_modify (context=0x7fffffff9c90, nb_node=0x5555556f4580, event=NB_EV_VALIDATE, dnode=0x5555557d0e20, resource=0x0, 
    errmsg=0x7fffffff9d90 "", errmsg_len=8192) at lib/northbound.c:1313
#3  0x00007ffff7d0defc in nb_callback_configuration (context=0x7fffffff9c90, event=NB_EV_VALIDATE, change=0x5555557d1680, errmsg=0x7fffffff9d90 "", 
    errmsg_len=8192) at lib/northbound.c:1666
#4  0x00007ffff7d0c3f8 in nb_candidate_validate_code (context=0x7fffffff9c90, candidate=0x5555556ad8f0, changes=0x7fffffff9ca0, errmsg=0x7fffffff9d90 "", 
    errmsg_len=8192) at lib/northbound.c:1021
#5  0x00007ffff7d0c67d in nb_candidate_commit_prepare (context=..., candidate=0x5555556ad8f0, comment=0x0, transaction=0x7fffffff9d30, skip_validate=false, 
    ignore_zero_change=false, errmsg=0x7fffffff9d90 "", errmsg_len=8192) at lib/northbound.c:1092
#6  0x00007ffff7d0c92c in nb_candidate_commit (context=..., candidate=0x5555556ad8f0, save_transaction=true, comment=0x0, transaction_id=0x0, 
    errmsg=0x7fffffff9d90 "", errmsg_len=8192) at lib/northbound.c:1156
#7  0x00007ffff7d13a9e in nb_cli_classic_commit (vty=0x5555557c78d0) at lib/northbound_cli.c:51
#8  0x00007ffff7d13c5e in nb_cli_pending_commit_check (vty=0x5555557c78d0) at lib/northbound_cli.c:90
#9  0x00007ffff7c9bb90 in cmd_execute_command_real (vline=0x5555556ff500, vty=0x5555557c78d0, cmd=0x0, up_level=0) at lib/command.c:999
#10 0x00007ffff7c9bd26 in cmd_execute_command (vline=0x5555556ff500, vty=0x5555557c78d0, cmd=0x0, vtysh=0) at lib/command.c:1061
#11 0x00007ffff7c9c2d6 in cmd_execute (vty=0x5555557c78d0, cmd=0x5555557ce0a0 " exit\n", matched=0x0, vtysh=0) at lib/command.c:1227
#12 0x00007ffff7d6832d in vty_command (vty=0x5555557c78d0, buf=0x5555557ce0a0 " exit\n") at lib/vty.c:600
#13 0x00007ffff7d6a251 in vty_execute (vty=0x5555557c78d0) at lib/vty.c:1363
#14 0x00007ffff7d6c97d in vtysh_read (thread=0x7fffffffe350) at lib/vty.c:2358
#15 0x00007ffff7d60f04 in event_call (thread=0x7fffffffe350) at lib/event.c:2011
#16 0x00007ffff7ce0ba7 in frr_run (master=0x5555555aae30) at lib/libfrr.c:1217
#17 0x0000555555577fca in main (argc=5, argv=0x7fffffffe5a8, envp=0x7fffffffe5d8) at eigrpd/eigrp_main.c:225
(gdb) ```




### Version

```text
This was introduced by this commit:
sharpd@eva ~/frr5 ((4caffbda…)|BISECTING)> git bisect bad
4caffbda8e6c690dc185b3740b203c2fa54e465e is the first bad commit
commit 4caffbda8e6c690dc185b3740b203c2fa54e465e
Author: Christian Hopps <chopps@labn.net>
Date:   Sat Feb 24 05:48:40 2024 -0500

    lib: add keychain northbound support
    
    Signed-off-by: Christian Hopps <chopps@labn.net>

How to reproduce

run mgmtd/zebra/eigrp( or rip or ospf or pim ) by hand then initiate a vtysh -b -n. Or you can just startup FRR as per normal with the above config snippet in frr.conf

Expected behavior

NO CRASHIE NO WHAMMY

Actual behavior

CRASHIE

Additional context

I like cats

Checklist

• I have searched the open issues for this bug.
• I have not included sensitive information in this report.

[idryzhov]

Should be fixed by #15771