cp: by popular demand, make it POSIX compliant (but less safe)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 19 insertions, 9 deletions

diff --git a/libbb/Config.in b/libbb/Config.in
index a572775c9..9b616d1af 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -114,6 +114,16 @@ config FEATURE_EDITING_ASK_TERMINAL
           correctly, or want to save on code size (about 300 bytes),
           then do not turn this option on.
 
+config FEATURE_NON_POSIX_CP
+        bool "Non-POSIX, but safer, copying to special nodes"
+        default y
+        help
+          With this option, "cp file symlink" will delete symlink
+          and create a regular file. This does not conform to POSIX,
+          but prevents a symlink attack.
+          Similarly, "cp file device" will not send file's data
+          to the device.
+
 config FEATURE_VERBOSE_CP_MESSAGE
         bool "Give more precise messages when copy fails (cp, mv etc)"
         default n
diff --git a/libbb/copy_file.c b/libbb/copy_file.c
index d804eccfa..4d2f17aa5 100644
--- a/libbb/copy_file.c
+++ b/libbb/copy_file.c
@@ -8,9 +8,10 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  *
  */
-
 #include "libbb.h"
 
+// FEATURE_NON_POSIX_CP:
+//
 // POSIX: if exists and -i, ask (w/o -i assume yes).
 // Then open w/o EXCL (yes, not unlink!).
 // If open still fails and -f, try unlink, then try open again.
@@ -23,22 +24,21 @@
 // NB: we have special code which still allows for "cp file /dev/node"
 // to work POSIX-ly (the only realistic case where it makes sense)
 
-#define DO_POSIX_CP 0  /* 1 - POSIX behavior, 0 - safe behavior */
-
 // errno must be set to relevant value ("why we cannot create dest?")
 // for POSIX mode to give reasonable error message
 static int ask_and_unlink(const char *dest, int flags)
 {
         int e = errno;
-#if DO_POSIX_CP
+#if !ENABLE_FEATURE_NON_POSIX_CP
         if (!(flags & (FILEUTILS_FORCE|FILEUTILS_INTERACTIVE))) {
                 // Either it exists, or the *path* doesnt exist
                 bb_perror_msg("cannot create '%s'", dest);
                 return -1;
         }
 #endif
-        // If !DO_POSIX_CP, act as if -f is always in effect - we don't want
-        // "cannot create" msg, we want unlink to be done (silently unless -i).
+        // If ENABLE_FEATURE_NON_POSIX_CP, act as if -f is always in effect
+        // - we don't want "cannot create" msg, we want unlink to be done
+        // (silently unless -i).
 
         // TODO: maybe we should do it only if ctty is present?
         if (flags & FILEUTILS_INTERACTIVE) {
@@ -279,10 +279,10 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
                  * non-interactive cp. NB: it is still racy
                  * for "cp file /home/bad_user/file" case
                  * (user can rm file and create a link to /etc/passwd) */
-                if (DO_POSIX_CP
+                if (!ENABLE_FEATURE_NON_POSIX_CP
                  || (dest_exists
-                     && !(flags & (FILEUTILS_RECUR|FILEUTILS_INTERACTIVE))
-                     && !S_ISLNK(dest_stat.st_mode))
+                    && !(flags & (FILEUTILS_RECUR|FILEUTILS_INTERACTIVE))
+                    && !S_ISLNK(dest_stat.st_mode))
                 ) {
                         dst_fd = open(dest, O_WRONLY|O_CREAT|O_TRUNC, new_mode);
                 } else  /* safe way: */