don't change owner/perms/times through file:// symlinks

If we have files in partial/ from a previous invocation or similar such
those could be symlinks created by file:// sources. The code is
expecting only real files through and happily changes owner,
modification times and permission on the file the symlink points to
which tend to be files we have no business in touching in this way.
Permissions of symlinks shouldn't be changed, changing owner is usually
pointless to, but just to be sure we pick the easy way out and use
lchown, check for symlinks before chmod/utimes.

Reported-By: Mattia Rizzolo on IRC

1 files changed, 4 insertions, 1 deletions

diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index c623f1a2a..e410f52d6 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -916,9 +916,12 @@ bool ChangeOwnerAndPermissionOfFile(char const * const requester, char const * c
       // ensure the file is owned by root and has good permissions
       struct passwd const * const pw = getpwnam(user);
       struct group const * const gr = getgrnam(group);
-      if (pw != NULL && gr != NULL && chown(file, pw->pw_uid, gr->gr_gid) != 0)
+      if (pw != NULL && gr != NULL && lchown(file, pw->pw_uid, gr->gr_gid) != 0)
 	 Res &= _error->WarningE(requester, "chown to %s:%s of file %s failed", user, group, file);
    }
+   struct stat Buf;
+   if (lstat(file, &Buf) != 0 || S_ISLNK(Buf.st_mode))
+      return Res;
    if (chmod(file, mode) != 0)
       Res &= _error->WarningE(requester, "chmod 0%o of file %s failed", mode, file);
    return Res;