> - free(allocated);
> + if (allocated)
> + free(allocated);
This is unnecessary, since free(NULL) is clearly defined as a no-op.
See the malloc(3) man page.
Tom
>>> Nan Xiao 4-Sep-17 12:11 >>>
>
> Hi tech@,
>
> This patch fixes the extreme case in dmesg.c: if memf or nlistf is not
> NULL, and "NOKVM" macro is defined.
>
> Current code in dmesg.c:
>
> struct msgbuf cur;
>
> Since "cur" is not initialized, so the following code has undefined
> behavior:
>
> if (cur.msg_bufx >= cur.msg_bufs)
> cur.msg_bufx = 0;
> /*
> * The message buffer is circular; start at the read pointer, and
> * go to the write pointer - 1.
> */
> for (newl = skip = i = 0, p = bufdata + cur.msg_bufx;
> i < cur.msg_bufs; i++, p++) {
> .....
> }
>
> My patch can skip the whole loop, and the "dmesg" program just prints
> a newline:
>
> if (!newl)
> putchar('\n');
>
> Best Regards
> Nan Xiao
>
> Index: dmesg.c
> ===================================================================
> RCS file: /cvs/src/sbin/dmesg/dmesg.c,v
> retrieving revision 1.29
> diff -u -p -r1.29 dmesg.c
> --- dmesg.c 1 Sep 2017 07:31:45 -0000 1.29
> +++ dmesg.c 4 Sep 2017 08:55:50 -0000
> @@ -65,12 +65,12 @@ main(int argc, char *argv[])
> int ch, newl, skip, i;
> char *p;
> struct msgbuf cur;
> - char *memf, *nlistf, *bufdata = NULL;
> + char *memf = NULL, *nlistf = NULL, *bufdata = NULL;
> char *allocated = NULL;
> int startupmsgs = 0;
> char buf[5];
>
> - memf = nlistf = NULL;
> + memset(&cur, 0, sizeof(cur));
> while ((ch = getopt(argc, argv, "sM:N:")) != -1)
> switch(ch) {
> case 's':
> @@ -184,7 +184,8 @@ main(int argc, char *argv[])
> }
> if (!newl)
> putchar('\n');
> - free(allocated);
> + if (allocated)
> + free(allocated);
> return (0);
> }
