bb_full_fd_action: remove potential xmalloc from NOFORK path

cat: stop using stdio.h opens
libbb: introduce & use open[3]_or_warn
function                                             old     new   delta
open3_or_warn                                          -      54     +54
bb_cat                                               115     144     +29
open_or_warn                                           -      25     +25
unlzma                                              2404    2412      +8
chattr_main                                          334     339      +5
xstrtoul_range_sfx                                   251     255      +4
telnet_main                                         1514    1510      -4
static.opt                                             4       -      -4
qgravechar                                           122     118      -4
fuser_add_pid                                         61      54      -7
fuser_add_inode                                      154     147      -7
writeFileToTarball                                  1542    1534      -8
refresh                                             1156    1148      -8
do_show                                              856     846     -10
read_leases                                          212     200     -12
setup_redirects                                      236     222     -14
iproute_list_or_flush                               1582    1568     -14
read_config                                          427     411     -16
write_leases                                         284     264     -20
hash_file                                            338     318     -20
copy_file                                           1760    1740     -20
do_iproute                                          2610    2588     -22
bb_full_fd_action                                    320     269     -51
open_to_or_warn                                      103      49     -54
fuser_main                                          1660    1596     -64
.rodata                                           131160  131096     -64
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 4/19 up/down: 125/-423)        Total: -298 bytes

3 files changed, 12 insertions, 10 deletions

diff --git a/coreutils/cat.c b/coreutils/cat.c
index eb141dc79..ed3f33650 100644
--- a/coreutils/cat.c
+++ b/coreutils/cat.c
@@ -19,18 +19,21 @@ int bb_cat(char **argv)
 {
         static const char *const argv_dash[] = { "-", NULL };
 
-        FILE *f;
+        int fd;
         int retval = EXIT_SUCCESS;
 
         if (!*argv)
                 argv = (char**) &argv_dash;
 
         do {
-                f = fopen_or_warn_stdin(*argv);
-                if (f) {
+                fd = STDIN_FILENO;
+                if (!LONE_DASH(*argv))
+                        fd = open_or_warn(*argv, O_RDONLY);
+                if (fd >= 0) {
                         /* This is not an xfunc - never exits */
-                        off_t r = bb_copyfd_eof(fileno(f), STDOUT_FILENO);
-                        fclose_if_not_stdin(f);
+                        off_t r = bb_copyfd_eof(fd, STDOUT_FILENO);
+                        if (fd != STDIN_FILENO)
+                                close(fd);
                         if (r >= 0)
                                 continue;
                 }
diff --git a/coreutils/dos2unix.c b/coreutils/dos2unix.c
index 1d35d524a..04c56ac9c 100644
--- a/coreutils/dos2unix.c
+++ b/coreutils/dos2unix.c
@@ -30,7 +30,7 @@ static int convert(char *fn)
                 /*
                    The file is then created with mode read/write and
                    permissions 0666 for glibc 2.0.6 and earlier or
-                   0600  for glibc  2.0.7 and  later.
+                   0600 for glibc 2.0.7 and later.
                  */
                 snprintf(bb_common_bufsiz1, sizeof(bb_common_bufsiz1), "%sXXXXXX", fn);
                 /*
@@ -38,8 +38,8 @@ static int convert(char *fn)
                    hold the full path.  However if the output is truncated the
                    subsequent call to mkstemp would fail.
                  */
-                if ((i = mkstemp(&bb_common_bufsiz1[0])) == -1
-                        || chmod(bb_common_bufsiz1, 0600) == -1) {
+                i = mkstemp(&bb_common_bufsiz1[0]);
+                if (i == -1 || chmod(bb_common_bufsiz1, 0600) == -1) {
                         bb_perror_nomsg_and_die();
                 }
                 out = fdopen(i, "w+");
diff --git a/coreutils/md5_sha1_sum.c b/coreutils/md5_sha1_sum.c
index 417e90b00..a3818d519 100644
--- a/coreutils/md5_sha1_sum.c
+++ b/coreutils/md5_sha1_sum.c
@@ -38,9 +38,8 @@ static uint8_t *hash_file(const char *filename, hash_algo_t hash_algo)
 
         src_fd = STDIN_FILENO;
         if (NOT_LONE_DASH(filename)) {
-                src_fd = open(filename, O_RDONLY);
+                src_fd = open_or_warn(filename, O_RDONLY);
                 if (src_fd < 0) {
-                        bb_perror_msg("%s", filename);
                         return NULL;
                 }
         }