stefan-mititelu-idt created an issue (kamailio/kamailio#4345)

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### Description Crash in kamailio 5.8.5 due to broken "next" pointer of circular double linked list of expired timers. <!-- Explain what you did, what you expected to happen, and what actually happened. -->

### Troubleshooting -

#### Reproduction Not easily reproducible <!-- If the issue can be reproduced, describe how it can be done. -->

#### Debugging Data

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gdb /path/to/kamailio /path/to/corefile bt full info locals list

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``` (gdb) bt full #0 timer_list_expire (slow_mark=<optimized out>, slow_l=0x7ff891b59d60, h=0x7ff891b56ff0, t=<optimized out>) at core/timer.c:850 tl = 0x7ff89d214810 ret = <optimized out> tl = <optimized out> ret = <optimized out> #1 timer_handler () at core/timer.c:925 saved_ticks = <optimized out> run_slow_timer = 0 i = <optimized out> saved_ticks = <optimized out> run_slow_timer = <optimized out> i = <optimized out> __func__ = "timer_handler" __llevel = <optimized out> __kld = {v_facility = <optimized out>, v_level = <optimized out>, v_lname = <optimized out>, v_fname = <optimized out>, v_fline = <optimized out>, v_mname = <optimized out>, v_func = <optimized out>, v_locinfo = <optimized out>, v_pid = <optimized out>, v_pidx = <optimized out>} __llevel = <optimized out> __kld = {v_facility = <optimized out>, v_level = <optimized out>, v_lname = <optimized out>, v_fname = <optimized out>, v_fline = <optimized out>, v_mname = <optimized out>, v_func = <optimized out>, v_locinfo = <optimized out>, v_pid = <optimized out>, v_pidx = <optimized out>} #2 timer_main () at core/timer.c:963 No locals. #3 0x000055e671830461 in main_loop () at main.c:1933 i = <optimized out> pid = <optimized out> si = 0x0 si_desc = "udp receiver child=15 sock=x.x.x.x:5080 (y.y.y.y:5080)", '\000' <repeats 16 times>, "\002\000\000\000\004\000\000\000\n_\022:\372\177\000\000\003\000\000\000\000\000\000\000\000kt\234s8\b\rThu Jul \a\000\000\000\000\000\000" nrprocs = <optimized out> woneinit = 1 __func__ = "main_loop" error = <optimized out> #4 0x000055e671824ff2 in main (argc=<optimized out>, argv=<optimized out>) at main.c:3257 cfg_stream = <optimized out> c = <optimized out> r = <optimized out> tmp = 0x7ffe2850be85 "" tmp_len = 0 port = 5060 proto = 0 aproto = 0 ahost = 0x0 aport = 0 options = 0x55e671bacd30 ":f:cm:M:dVIhEeb:B:l:L:n:vKrRDTN:W:w:t:u:g:P:G:SQ:O:a:A:x:X:Y:" ret = -1 seed = 1220594137 rfd = <optimized out> debug_save = <optimized out> debug_flag = <optimized out> --Type <RET> for more, q to quit, c to continue without paging-- dont_fork_cnt = <optimized out> n_lst = <optimized out> p = <optimized out> st = {st_dev = 22, st_ino = 1081, st_nlink = 2, st_mode = 16888, st_uid = 109, st_gid = 115, __pad0 = 0, st_rdev = 0, st_size = 40, st_blksize = 4096, st_blocks = 0, st_atim = {tv_sec = 1751525619, tv_nsec = 801181720}, st_mtim = {tv_sec = 1751525619, tv_nsec = 117175705}, st_ctim = {tv_sec = 1751525636, tv_nsec = 937332387}, __glibc_reserved = {0, 0, 0}} l1 = <optimized out> tbuf = "\000\000\000\000\000\000\000\000\030"U(\376\177\000\000\000\000\000\000 ", '\000' <repeats 27 times>, "\001\000\000\000\000\000\000\000\366u\256\003\001", '\000' <repeats 67 times>, "\060Wj\242\372\177\000\000\004\000\000\024\000\000\000\000@!k\242\372\177", '\000' <repeats 138 times>, "\020\000\000\000\000\000\000\000 \265P(\376\177\000\000\020\000\000\000\376\177\000\000\060\265P(\376\177\000\000\370\264P(\376\177\000\000x\221\205\242\372\177\000\000\300\t\000\000\300\t\000\000x\221\205\242\372\177\000\000\300\t\000\000\300\t\000\000L\206\204\242\372\177\000\000\300\t\000\000\300\t\000\000L\206\204\242\372\177\000\000\300\t\000\000\300\t\000\000\300\t\000\000\300\t\000\000\377\377\377\377\000\000\000\000\020_\202\242\372\177\000\000H\000\000\000\000\000\000\000\312<k\242\372\177\000\000`\200\205\242d\000\000\000\000kt\234s8\b\r\377\377\377\377\000\000\000\000j[j\242\372\177\000\000\000\000\000\000\000\000\000\000@\000\000\000\000\000\000\000\000\000\200\000\000\000\000\000\377\377\377\377\377\377\377\377\377\265\360\000\000\000\000\000\302\000\000\000\000\000\000" option_index = 12 long_options = {{name = 0x55e671bab333 "help", has_arg = 0, flag = 0x0, val = 104}, {name = 0x55e671bb4a8e "version", has_arg = 0, flag = 0x0, val = 118}, { name = 0x55e671bc48d1 "alias", has_arg = 1, flag = 0x0, val = 1024}, {name = 0x55e671bab338 "subst", has_arg = 1, flag = 0x0, val = 1025}, { name = 0x55e671bab33e "substdef", has_arg = 1, flag = 0x0, val = 1026}, {name = 0x55e671bab347 "substdefs", has_arg = 1, flag = 0x0, val = 1027}, { name = 0x55e671bab351 "server-id", has_arg = 1, flag = 0x0, val = 1028}, {name = 0x55e671bab35b "loadmodule", has_arg = 1, flag = 0x0, val = 1029}, { name = 0x55e671bab366 "modparam", has_arg = 1, flag = 0x0, val = 1030}, {name = 0x55e671bab36f "log-engine", has_arg = 1, flag = 0x0, val = 1031}, { name = 0x55e671bb4bab "debug", has_arg = 1, flag = 0x0, val = 1032}, {name = 0x55e671bab37a "cfg-print", has_arg = 0, flag = 0x0, val = 1033}, { name = 0x55e671bab384 "atexit", has_arg = 1, flag = 0x0, val = 1034}, {name = 0x55e671bab38b "all-errors", has_arg = 0, flag = 0x0, val = 1035}, {name = 0x0, has_arg = 0, flag = 0x0, val = 0}} __func__ = "main" ```

Some more debugging info: ``` (gdb) p tl $203 = (struct timer_ln *) 0x7ff89d214810 (gdb) p h $202 = (struct timer_head *) 0x7ff891b56ff0

(gdb) p *(struct timer_ln *) 0x7ff891e21af0 $6 = {next = 0x7ff891e24b00, prev = 0x7ff89d214810, expire = 1057066680, initial_timeout = 480, data = 0x7ff891e21af0, f = 0x55e671a570a0 <compat_old_handler>, flags = 512, slow_idx = 0} (gdb) p *tl $205 = {next = 0x0, prev = 0x7ff891b56ff0, expire = 1057066648, initial_timeout = 48, data = 0xfffffffe, f = 0x7ffa91f77e30 <retr_buf_handler>, flags = 512, slow_idx = 0} (gdb) p *h $204 = {next = 0x0, prev = 0x7ff891e00e10} (gdb) p *(struct timer_ln *) 0x7ff891e00e10 $7 = {next = 0x7ff891b56ff0, prev = 0x7ff89e47d538, expire = 1057066680, initial_timeout = 16, data = 0x7ff891e00e10, f = 0x55e671a570a0 <compat_old_handler>, flags = 512, slow_idx = 0}

(gdb) p h->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev $198 = (struct timer_ln *) 0x7ff891e21af0 (gdb) p h->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev $199 = (struct timer_ln *) 0x7ff89d214810 (gdb) p h->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev $200 = (struct timer_ln *) 0x7ff891b56ff0 (gdb) p h->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev->prev $201 = (struct timer_ln *) 0x7ff891e00e10 ```

#### Log Messages

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``` (paste your log messages here) ```

#### SIP Traffic

<!-- If the issue is exposed by processing specific SIP messages, grab them with ngrep or save in a pcap file, then add them next, or attach to issue, or provide a link to download them (e.g., to a pastebin site). -->

``` (gdb) p *(struct retr_buf *)((char *)(tl)-((size_t)((char *)&((struct retr_buf*)(0))->timer - (char *)0))) $13 = {rbtype = 0, flags = 164, t_active = 0, branch = 0, buffer_len = 1021, buffer = 0x7ff897731ef0 "KDMQ sip:usrloc@x.x.x.x:5040;transport=tcp SIP/2.0\r\nVia: SIP/2.0/TCP y.y.y.y:5045;branch=z9hG4bK6411.2eec64c5", '0' <repeats 24 times>, ".0\r\nTo: sip:usrloc@x.x.x.x:5040;transport=tcp\r\nFrom: sip:usrloc@y.y.y.y:5040;transport=tcp;tag=ea5c1e4b006551edd6973f0c22cc35ec-9c6994fe\r\nCSeq: 10 KDMQ\r\nCall-ID: 3bc128ce41f9d5e5-3737@x.x.x.x\r\nContent-Length: 574\r\nUser-Agent: UNITE 3.0\r\nMax-Forwards: 1\r\nContent-Type: application/json\r\n\r\n{"action":1,"aor":"01537833832a5ccc75058ef5839f","ruid":"uloc-a71cb2-68662908-e99-e6b85","c":"sip:01537833832a5ccc75058ef5839f@z.z.z.z:11916;transport=TCP","received":"sip:x.x.x.x:11916;transport=tcp","path":"sip:z.z.z.z:5040;transport=tcp;lr;received=sip:w.w.w.w:11916%3Btransport%3Dtcp;socket=clientTCPListener","callid":"0_912990869@192.168.1.7","user_agent":"Yealink SIP-T30 t.t.t.t","instance":"","expires":1751822448,"cseq":28,"flags":0,"cflags":96,"q":-1,"last_modified":1751822148,"methods":16383,"reg_id":0,"server_id":10951858,"xavps":{}}", my_T = 0x7ff89d214510, timer = {next = 0x0, prev = 0x7ff891b56ff0, expire = 1057066648, initial_timeout = 48, data = 0xfffffffe, f = 0x7ffa91f77e30 <retr_buf_handler>, flags = 512, slow_idx = 0}, dst = {send_sock = 0x7ffa9264fae0, to = {s = {sa_family = 2, sa_data = "\023\260\n_\020\210\000\000\000\000\000\000\000"}, sin = {sin_family = 2, sin_port = 45075, sin_addr = {s_addr = 2282774282}, sin_zero = "\000\000\000\000\000\000\000"}, sin6 = {sin6_family = 2, sin6_port = 45075, sin6_flowinfo = 2282774282, sin6_addr = {__in6_u = { __u6_addr8 = '\000' <repeats 15 times>, __u6_addr16 = {0, 0, 0, 0, 0, 0, 0, 0}, __u6_addr32 = {0, 0, 0, 0}}}, sin6_scope_id = 0}, sas = {ss_family = 2, __ss_padding = "\023\260\n_\020\210", '\000' <repeats 111 times>, __ss_align = 0}}, id = 0, send_flags = {f = 4, blst_imask = 0}, proto = 2 '\002', proto_pad0 = 0 '\000', proto_pad1 = 0}, retr_expire = 1057066599, fr_expire = 1057066648} ```

### Possible Solutions Check if "next" list is broken and recover the pointers form "prev" list, and viceversa.

<!-- If you found a solution or workaround for the issue, describe it. Ideally, provide a pull request with a fix. -->

### Additional Information Using 1s transaction timeout for KDMQs.

* **Kamailio Version** - output of `kamailio -v`

``` 5.8.5 kamailio version ```

* **Operating System**: <!-- Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...; Kernel details (output of `lsb_release -a` and `uname -a`) -->

```

Debian 11 ```