[Bug-readline] Memory error in read_history_range

[Denis Martinez]

When I tried to get Readline working with ECL Common Lisp, I have
discovered a memory error which occurs in a particular situation.

Valgrind reports an invalid read when invoking read_history() on an
existing but empty history file. This is easily reproduced with a
trivial test program (readline 7.0.003, Arch GNU/Linux x86_64).

#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h>
int main(int argc, char *argv[]) {
  if (argc != 2) return 1;
  read_history(argv[1]);
  return 0;
}

The valgrind report points at two distinct points in 
histfile.c/read_history_range()
where the same memory error happens.

l.353:  if (history_comment_char == '\0' && buffer[0] == '#' && isdigit 
((unsigned char)buffer[1]))
l.359:  has_timestamps = HIST_TIMESTAMP_START (buffer);

An error occurs because buffer is assumed to be a 0-terminated string,
however it is not.

The code which previously reads into buffer does not write the 0 terminator
after the data. This problem could be solved by writing
`buffer[chars_read] = 0' in the success path following read().

Please also note: the MMAP path, which also does not terminate input,
seems equally fallible given an input whose exact content is the character #.