bug#22489: A bug in tail.c

[Lei Wang]

Version: GNU Coreutils 8.20-8.25 ​
File: tail.c
Bug description:
Line 1979,  parse_obsolete_option() function  has three parameters: argc,
argv, n_units.  We only need to focus on argc and argv, which is from the
main() function. Line 1992  filter  the argc and argv. When argc==2,  line
1998 p = argv[1], line 2000 *p++, then *p=argv[1][1], line 2026 while
(ISDIGIT (*p)) access p. There is one condition can lead to program
overflow, thus argc==2 and argv[1] has only one character, for example
./tail x , will access the next character after x, this maybe a bug, but
can not lead program crash.
--WangLei