Description of problem:
GNU Tar reproducibly crashes with a complaint of a "buffer overflow detected" + SIGABRT when passing certain contents through the TAR_OPTIONS environment variable.

I am providing a simplified reproducer from a real-world upstream attempt to build fetchmail in a reproducible manner, and a decoded core dump from the real application.  See stack frames #7...#14 below.

(This might be security relevant in SaaS settings where the tar environment isn't under control; in my case, it is.)

Version-Release number of selected component (if applicable):
1.35-5.fc42 (x86_64)


How reproducible:
always

Steps to Reproduce:
1. env 'TAR_OPTIONS=--mtime="@1234567890"' /usr/bin/tar --format=ustar -chf - . >/dev/null

Actual results:
*** buffer overflow detected ***: terminated
Aborted (core dumped)

Expected results:
tar archive properly created (and discarded -- normally I would redirect into xz -c to compress, with output redirection)

Additional info:
I can't apparently properly report through abrt which claims that the core couldn't be usefully decoded, but coredumpctl debug <PID> came up with this pretty elucidating backtrace from the original application (NOT the synthesized reproducer given above).

Removing the quote marks from the --mtime argument passed through TAR_OPTIONS fixes the crash.

#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
        tid = <optimized out>
        ret = 0
        pd = <optimized out>
        old_mask = {__val = {140543246097462}}
        ret = <optimized out>
#1  0x00007fd2c641e163 in __pthread_kill_internal (threadid=<optimized out>, signo=6) at pthread_kill.c:89
No locals.
#2  0x00007fd2c63c4a7e in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
        ret = <optimized out>
#3  0x00007fd2c63ac6d0 in __GI_abort () at abort.c:77
        act = {__sigaction_handler = {sa_handler = 0x559a00000000, sa_sigaction = 0x559a00000000}, sa_mask = {__val = {0, 94121436579136, 8, 140734169646992, 779909072403883264, 94121436579136, 0, 0, 335544320, 140543245700016, 65536, 94119913324560, 140543246595678, 
              4096, 140543247367818, 976259312}}, sa_flags = 1371333888, sa_restorer = 0x7fd2c655e2da}
#4  0x00007fd2c63ad6f3 in __libc_message_impl (fmt=fmt@entry=0x7fd2c655e2c3 "*** %s ***: terminated\n") at ../sysdeps/posix/libc_fatal.c:134
        ap = {{gp_offset = 16, fp_offset = 32767, overflow_arg_area = 0x7fff3a3087f0, reg_save_area = 0x7fff3a308780}}
        fd = 2
        iov = {{iov_base = 0x7fd2c655e2c3, iov_len = 4}, {iov_base = 0x7fd2c655e2aa, iov_len = 24}, {iov_base = 0x7fd2c655e2c9, iov_len = 17}, {iov_base = 0x0, iov_len = 94121436574688}, {iov_base = 0x559a5acaf680, iov_len = 0}, {iov_base = 0x2475acaf3e0, 
            iov_len = 40}, {iov_base = 0x559a5acb1550, iov_len = 0}}
        iovcnt = <optimized out>
        total = <optimized out>
        cp = <optimized out>
#5  0x00007fd2c64aa549 in __GI___fortify_fail (msg=msg@entry=0x7fd2c655e2aa "buffer overflow detected") at fortify_fail.c:24
No locals.
#6  0x00007fd2c64a9ea4 in __GI___chk_fail () at chk_fail.c:28
No locals.
#7  0x0000559a384b0c6e in memcpy (__dest=<optimized out>, __src=<optimized out>, __len=11) at /usr/include/bits/string_fortified.h:29
No locals.
#8  coalesce_segment (wsp=wsp@entry=0x7fff3a3089b0, node=node@entry=0x559a5acb1580) at ../lib/wordsplit.c:598
        next = 0x0
        str = <optimized out>
        slen = 11
        p = 0x559a5acb15b0
        end = 0x559a5acb15b0
        len = 8
        buf = 0x559a5acb05a0 "--mtime="
        cur = <optimized out>
#9  0x0000559a384b574a in wsnode_coalesce (wsp=0x7fff3a3089b0) at ../lib/wordsplit.c:675
        p = 0x559a5acb1580
#10 wordsplit_process_list (wsp=0x7fff3a3089b0, start=<optimized out>) at ../lib/wordsplit.c:2379
        p = 0x559a384e5d10 <exptab+48>
#11 0x0000559a384bc15b in wordsplit_run (lvl=0, command=0x7fff3a30a4cf "--owner=0 --group=0 --sort=name --mtime=\"@1752234285\"", length=<optimized out>, wsp=0x7fff3a3089b0, flags=33558086) at ../lib/wordsplit.c:2434
        rc = <optimized out>
        start = 0
#12 wordsplit_len (command=0x7fff3a30a4cf "--owner=0 --group=0 --sort=name --mtime=\"@1752234285\"", length=<optimized out>, wsp=0x7fff3a3089b0, flags=33558086) at ../lib/wordsplit.c:2444
No locals.
#13 wordsplit (command=0x7fff3a30a4cf "--owner=0 --group=0 --sort=name --mtime=\"@1752234285\"", ws=0x7fff3a3089b0, flags=33558086) at ../lib/wordsplit.c:2450
No locals.
#14 0x0000559a3847f47e in parse_default_options (args=0x7fff3a308980) at /usr/src/debug/tar-1.35-5.fc42.x86_64/src/tar.c:2256
        opts = <optimized out>
        ws = {ws_wordc = 0, ws_wordv = 0x0, ws_offs = 1, ws_wordn = 0, ws_flags = 33558086, ws_options = 1632, ws_maxwords = 140543247636624, ws_wordi = 0, ws_delim = 0x559a384d0cd1 " \t\n", ws_comment = 0x0, ws_escape = {
            0x559a384e5c90 <wordsplit_c_escape_tab> "\\\\\"\"a\ab\bf\fn\nr\rt\tv\v", 0x559a384e5c90 <wordsplit_c_escape_tab> "\\\\\"\"a\ab\bf\fn\nr\rt\tv\v"}, ws_alloc_die = 0x559a384af9c0 <_wsplt_alloc_die>, ws_error = 0x559a384b09f0 <_wsplt_error>, ws_debug = 0x0, 
          ws_env = 0x15, ws_envbuf = 0x100a, ws_envidx = 255, ws_envsiz = 4185718668, ws_getvar = 0x0, ws_closure = 0x0, ws_command = 0xf97cff8c, ws_input = 0x7fff3a30a4cf "--owner=0 --group=0 --sort=name --mtime=\"@1752234285\"", ws_len = 53, ws_endp = 53, 
          ws_errno = 0, ws_usererr = 0x0, ws_head = 0x559a5acb14f0, ws_tail = 0x559a5acb15b0, ws_lvl = 0}
        loc = {source = OPTS_ENVIRON, name = 0x559a384d0d6f "TAR_OPTIONS", line = 0, prev = 0x0}
        save_loc_ptr = <optimized out>
#15 decode_options (argc=5, argv=0x7fff3a308bf8) at /usr/src/debug/tar-1.35-5.fc42.x86_64/src/tar.c:2378
        idx = 32767
        loc = {source = OPTS_COMMAND_LINE, name = 0x0, line = 0, prev = 0x0}
        args = {loc = 0x7fff3a308940, textual_date = 0x0, o_option = false, pax_option = false, compress_autodetect = false, backup_suffix_string = 0x0, version_control_string = 0x0}
#16 main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/tar-1.35-5.fc42.x86_64/src/tar.c:2792
No locals.