cp: make "non-POSIX" cp a bit more consistent

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

1 files changed, 28 insertions, 34 deletions

diff --git a/libbb/copy_file.c b/libbb/copy_file.c
index 4d2f17aa5..ae70cbc0a 100644
--- a/libbb/copy_file.c
+++ b/libbb/copy_file.c
@@ -6,7 +6,6 @@
  * SELinux support by Yuichi Nakamura <ynakam@hitachisoft.jp>
  *
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
- *
  */
 #include "libbb.h"
 
@@ -16,31 +15,33 @@
 // Then open w/o EXCL (yes, not unlink!).
 // If open still fails and -f, try unlink, then try open again.
 // Result: a mess:
-// If dest is a softlink, we overwrite softlink's destination!
+// If dest is a (sym)link, we overwrite link destination!
 // (or fail, if it points to dir/nonexistent location/etc).
 // This is strange, but POSIX-correct.
 // coreutils cp has --remove-destination to override this...
-//
-// 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)
 
-// errno must be set to relevant value ("why we cannot create dest?")
-// for POSIX mode to give reasonable error message
+/* Called if open of destination, link creation etc fails.
+ * errno must be set to relevant value ("why we cannot create dest?")
+ * to give reasonable error message */
 static int ask_and_unlink(const char *dest, int flags)
 {
         int e = errno;
+
 #if !ENABLE_FEATURE_NON_POSIX_CP
         if (!(flags & (FILEUTILS_FORCE|FILEUTILS_INTERACTIVE))) {
-                // Either it exists, or the *path* doesnt exist
+                /* Either it exists, or the *path* doesnt exist */
                 bb_perror_msg("cannot create '%s'", dest);
                 return -1;
         }
 #endif
-        // 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).
+        // else: act as if -f is always in effect.
+        // We don't want "cannot create" msg, we want unlink to be done
+        // (silently unless -i). Why? POSIX cp usually succeeds with
+        // O_TRUNC open of existing file, and user is left ignorantly happy.
+        // With above block unconditionally enabled, non-POSIX cp
+        // will complain a lot more than POSIX one.
 
-        // TODO: maybe we should do it only if ctty is present?
+        /* TODO: maybe we should do it only if ctty is present? */
         if (flags & FILEUTILS_INTERACTIVE) {
                 // We would not do POSIX insanity. -i asks,
                 // then _unlinks_ the offender. Presto.
@@ -48,7 +49,7 @@ static int ask_and_unlink(const char *dest, int flags)
                 // Or else we will end up having 3 open()s!
                 fprintf(stderr, "%s: overwrite '%s'? ", applet_name, dest);
                 if (!bb_ask_confirmation())
-                        return 0; // not allowed to overwrite
+                        return 0; /* not allowed to overwrite */
         }
         if (unlink(dest) < 0) {
 #if ENABLE_FEATURE_VERBOSE_CP_MESSAGE
@@ -56,14 +57,14 @@ static int ask_and_unlink(const char *dest, int flags)
                         /* e == ENOTDIR is similar: path has non-dir component,
                          * but in this case we don't even reach copy_file() */
                         bb_error_msg("cannot create '%s': Path does not exist", dest);
-                        return -1; // error
+                        return -1; /* error */
                 }
 #endif
-                errno = e;
+                errno = e; /* do not use errno from unlink */
                 bb_perror_msg("cannot create '%s'", dest);
-                return -1; // error
+                return -1; /* error */
         }
-        return 1; // ok (to try again)
+        return 1; /* ok (to try again) */
 }
 
 /* Return:
@@ -85,8 +86,8 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
 #define FLAGS_DEREF (flags & FILEUTILS_DEREFERENCE)
 
         if ((FLAGS_DEREF ? stat : lstat)(source, &source_stat) < 0) {
-                // This may be a dangling symlink.
-                // Making [sym]links to dangling symlinks works, so...
+                /* This may be a dangling symlink.
+                 * Making [sym]links to dangling symlinks works, so... */
                 if (flags & (FILEUTILS_MAKE_SOFTLINK|FILEUTILS_MAKE_HARDLINK))
                         goto make_links;
                 bb_perror_msg("cannot stat '%s'", source);
@@ -212,9 +213,9 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
         if (flags & (FILEUTILS_MAKE_SOFTLINK|FILEUTILS_MAKE_HARDLINK)) {
                 int (*lf)(const char *oldpath, const char *newpath);
  make_links:
-                // Hmm... maybe
-                // if (DEREF && MAKE_SOFTLINK) source = realpath(source) ?
-                // (but realpath returns NULL on dangling symlinks...)
+                /* Hmm... maybe
+                 * if (DEREF && MAKE_SOFTLINK) source = realpath(source) ?
+                 * (but realpath returns NULL on dangling symlinks...) */
                 lf = (flags & FILEUTILS_MAKE_SOFTLINK) ? symlink : link;
                 if (lf(source, dest) < 0) {
                         ovr = ask_and_unlink(dest, flags);
@@ -226,7 +227,7 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
                         }
                 }
                 /* _Not_ jumping to preserve_mode_ugid_time:
-                 * hard/softlinks don't have those */
+                 * (sym)links don't have those */
                 return 0;
         }
 
@@ -274,19 +275,12 @@ int FAST_FUNC copy_file(const char *source, const char *dest, int flags)
                 if (!S_ISREG(source_stat.st_mode))
                         new_mode = 0666;
 
-                /* POSIX way is a security problem versus symlink attacks,
-                 * we do it only for non-symlinks, and only for non-recursive,
-                 * 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 (!ENABLE_FEATURE_NON_POSIX_CP
-                 || (dest_exists
-                    && !(flags & (FILEUTILS_RECUR|FILEUTILS_INTERACTIVE))
-                    && !S_ISLNK(dest_stat.st_mode))
-                ) {
+                // POSIX way is a security problem versus (sym)link attacks
+                if (!ENABLE_FEATURE_NON_POSIX_CP) {
                         dst_fd = open(dest, O_WRONLY|O_CREAT|O_TRUNC, new_mode);
-                } else  /* safe way: */
+                } else { /* safe way: */
                         dst_fd = open(dest, O_WRONLY|O_CREAT|O_EXCL, new_mode);
+                }
                 if (dst_fd == -1) {
                         ovr = ask_and_unlink(dest, flags);
                         if (ovr <= 0) {