history -r a; history -c; history -r b gives segfault

[Edward Huff]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-redhat-linux-gnu'
-DCONF_VENDOR='redhat' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash'
-DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib  -D_GNU_SOURCE
-DRECYCLES_PIDS -DDEFAULT_PATH_VALUE='/usr/local/bin:/usr/bin'  -O2 -g
-pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
-Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong
-grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
-specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
-fasynchronous-unwind-tables -fstack-clash-protection -mcet -fcf-protection
-Wno-parentheses -Wno-format-security
uname output: Linux elite.mainst 4.16.12-300.fc28.x86_64 #1 SMP Fri May 25
21:13:28 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-redhat-linux-gnu

Bash Version: 4.4
Patch Level: 19
Release Status: release

Description:
Segfault from reading a history file not starting with # with
HISTTIMEFORMAT set and history_multiline_entries nonzero and
with the history cleared and read on the same input line.

Repeat-By:

env -i bash --noprofile --norc
echo $'#1\necho a'>a
echo 'echo b'>b
HISTTIMEFORMAT='%s '
history -r a # force history_multiline_entries to be nonzero
history -c; history -r b # force history_length to be zero when reading
Segmentation fault (core dumped)

Fix:

history_multiline_entries probably shouldn't be sticky over unset
HISTTIMEFORMAT, but here is the minimal fix:

--- /usr/src/debug/bash-4.4.19-2.fc28.x86_64/lib/readline/histfile.c
2016-01-25 10:34:03.000000000 -0500
+++ histfile.c    2018-06-10 03:12:17.750218417 -0400
@@ -385,7 +385,7 @@
       {
         if (HIST_TIMESTAMP_START(line_start) == 0)
           {
-              if (last_ts == NULL && history_multiline_entries)
+              if (history_length > 0 && last_ts == NULL &&
history_multiline_entries)
           _hs_append_history_line (history_length - 1, line_start);
         else
           add_history (line_start);