win32: restrict visibility of special devices

Handling of the special devices /dev/zero and /dev/urandom was
inconsistent:

- they could be used as arguments to 'cat' but not 'od';
- they could not be used in shell redirection.

Restrict the use of these devices to two places:

- as input files to 'dd' with the 'if=' argument;
- internally within 'shred'.

See GitHub issue #98.

4 files changed, 33 insertions, 8 deletions

diff --git a/coreutils/dd.c b/coreutils/dd.c
index 4362ae798..10066575e 100644
--- a/coreutils/dd.c
+++ b/coreutils/dd.c
@@ -429,8 +429,10 @@ int dd_main(int argc UNUSED_PARAM, char **argv)
 #endif
 
         if (infile) {
+#if !ENABLE_PLATFORM_MINGW32
                 xmove_fd(xopen(infile, O_RDONLY), ifd);
-#if ENABLE_PLATFORM_MINGW32
+#else
+                xmove_fd(mingw_xopen(infile, O_RDONLY), ifd);
                 if (!strcmp(infile, "/dev/zero")) {
                         mingw_read_zero(ifd);
                 }
diff --git a/coreutils/shred.c b/coreutils/shred.c
index 1b65a359e..0ebbc39ca 100644
--- a/coreutils/shred.c
+++ b/coreutils/shred.c
@@ -38,6 +38,10 @@
 
 #include "libbb.h"
 
+#if ENABLE_PLATFORM_MINGW32
+#define xopen mingw_xopen
+#endif
+
 int shred_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int shred_main(int argc UNUSED_PARAM, char **argv)
 {
diff --git a/include/mingw.h b/include/mingw.h
index 09903d582..386540b37 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -30,6 +30,7 @@ int inet_pton(int af, const char *src, void *dst);
 #define FD_CLOEXEC 0x1
 #define O_NONBLOCK 0
 #define O_NOFOLLOW 0
+#define O_SPECIAL 0x800000
 
 /*
  * grp.h
@@ -367,6 +368,7 @@ int kill(pid_t pid, int sig);
 int link(const char *oldpath, const char *newpath);
 NOIMPL(mknod,const char *name UNUSED_PARAM, mode_t mode UNUSED_PARAM, dev_t device UNUSED_PARAM);
 int mingw_open (const char *filename, int oflags, ...);
+int mingw_xopen(const char *filename, int oflags);
 void mingw_read_zero(int fd);
 void mingw_read_random(int fd);
 ssize_t mingw_read(int fd, void *buf, size_t count);
diff --git a/win32/mingw.c b/win32/mingw.c
index f9967f1c4..981c50415 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -157,6 +157,7 @@ int mingw_open (const char *filename, int oflags, ...)
         va_list args;
         unsigned mode;
         int fd;
+        int special = 0;
         int devnull = 0;
         int devzero = 0;
         int devrand = 0;
@@ -165,16 +166,20 @@ int mingw_open (const char *filename, int oflags, ...)
         mode = va_arg(args, int);
         va_end(args);
 
-        if (oflags & O_NONBLOCK) {
-                oflags &= ~O_NONBLOCK;
+        if (oflags & O_SPECIAL) {
+                oflags &= ~O_SPECIAL;
+                special = 1;
         }
         if (filename && !strncmp(filename, "/dev/", 5)) {
-                if (!strcmp(filename+5, "null"))
+                if (!strcmp(filename+5, "null")) {
                         devnull = 1;
-                else if (!strcmp(filename+5, "zero"))
-                        devzero = 1;
-                else if (!strcmp(filename+5, "urandom"))
-                        devrand = 1;
+                }
+                else if (special) {
+                        if (!strcmp(filename+5, "zero"))
+                                devzero = 1;
+                        else if (!strcmp(filename+5, "urandom"))
+                                devrand = 1;
+                }
 
                 if (devnull || devzero || devrand )
                         filename = "nul";
@@ -194,6 +199,18 @@ int mingw_open (const char *filename, int oflags, ...)
         return fd;
 }
 
+int mingw_xopen(const char *pathname, int flags)
+{
+        int ret;
+
+        /* allow use of special devices */
+        ret = mingw_open(pathname, flags|O_SPECIAL);
+        if (ret < 0) {
+                bb_perror_msg_and_die("can't open '%s'", pathname);
+        }
+        return ret;
+}
+
 #undef fopen
 FILE *mingw_fopen (const char *filename, const char *otype)
 {