fixes for coverity warnings to cat(1)

[Sevan Janiyan]

Hi,
Attached is a diff for a couple of issues raised by coverity, obtained
from NetBSD src/bin/cat/cat.c r1.53 & r1.54

>From the commit message in NetBSD CVS:
"bin/cat/cat.c 976654 Argument cannot be negative
                     (missing check for fileno result, stdout)
bin/cat/cat.c 976653 Improper use of negative value
                     (missing check for fileno result, stdin)"

Diff also adds a skip label used by the changes which appeared in NetBSD
at a different revision in the past.


Sevan Janiyan

From NetBSD
cat.c r1.53 r1.54

Index: bin/cat/cat.c
===================================================================
RCS file: /cvs/src/bin/cat/cat.c,v
retrieving revision 1.21
diff -u -r1.21 cat.c
--- bin/cat/cat.c       16 Jan 2015 06:39:28 -0000      1.21
+++ bin/cat/cat.c       20 Jul 2015 23:08:00 -0000
@@ -200,15 +200,20 @@
        filename = "stdin";
        do {
                if (*argv) {
-                       if (!strcmp(*argv, "-"))
+                       if (!strcmp(*argv, "-")) {
                                fd = fileno(stdin);
-                       else if ((fd = open(*argv, O_RDONLY, 0)) < 0) {
+                               if (fd < 0)
+                                       goto skip;
+                       } else if ((fd = open(*argv, O_RDONLY, 0)) < 0) {
+skip:
                                warn("%s", *argv);
                                rval = 1;
                                ++argv;
                                continue;
                        }
                        filename = *argv++;
+               } else if (fd < 0) {
+                       err(1, "stdin");
                }
                raw_cat(fd);
                if (fd != fileno(stdin))
@@ -226,6 +231,8 @@
        struct stat sbuf;
 
        wfd = fileno(stdout);
+       if (wfd < 0)
+               err(1, "stdout");
        if (buf == NULL) {
                if (fstat(wfd, &sbuf))
                        err(1, "stdout");