bug#49287: sed -i disrespects read-only

[Leonid Mironov]

   Hello,

   sed disrespects read-only file attributes when editing in place.

   $ ls -l testfile*
   -r--r--r-- 1 lvm lvm 50 Jun 30 08:32 testfile
   $ sed 's/test/bug/g' -i~ testfile
   $ diff testfile testfile~
   2c2
   < this is a bug
   ---
   > this is a test
   $ sed --version
   sed (GNU sed) 4.4
   Copyright © 2017 Free Software Foundation, Inc.
   Licence GPLv3+: GNU GPL version 3 or later
   <[1]https://www.gnu.org/licenses/gpl.html>.
   This is free software: you are free to change and redistribute it.
   There is NO WARRANTY, to the extent permitted by law.
   Written by Jay Fenlason, Tom Lord, Ken Pizzini,
   and Paolo Bonzini.
   GNU sed home page: <[2]http://www.gnu.org/software/sed/>.
   General help using GNU software: <[3]http://www.gnu.org/gethelp/>.
   E-mail bug reports to: <bug-sed@gnu.org>.
   $ uname -a
   Linux server 5.4.0-74-generic #83~18.04.1-Ubuntu SMP Tue May 11
   16:01:00 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux


   Not the latest version, but buiding latest git sources fails with

     CC       sed/sed_sed-execute.o
   sed/execute.c: In function 'open_next_file':
   sed/execute.c:575:7: error: unknown type name 'security_context_t'; did
   you mean 'security_class_t'?
          security_context_t old_fscreatecon;
          ^~~~~~~~~~~~~~~~~~
          security_class_t
   sed/execute.c:596:11: error: unknown type name 'security_context_t';
   did you mean 'security_class_t'?
              security_context_t con;
              ^~~~~~~~~~~~~~~~~~
              security_class_t
   sed/execute.c:597:49: error: passing argument 2 of 'lgetfilecon' from
   incompatible pointer type [-Werror=incompatible-pointer-types]
              if (lgetfilecon (input->in_file_name, &con) != -1)
                                                    ^
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:104:1: note: expected 'char **' but argument is
   of type 'int *'
    lgetfilecon (char const *file _GL_UNUSED_PARAMETER,
    ^~~~~~~~~~~
   sed/execute.c:601:51: error: passing argument 1 of 'getfscreatecon'
   from incompatible pointer type [-Werror=incompatible-pointer-types]
                  reset_fscreatecon = getfscreatecon (&old_fscreatecon) >=
   0;
                                                      ^
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:89:1: note: expected 'char **' but argument is
   of type 'int *'
    getfscreatecon (char **con _GL_UNUSED_PARAMETER)
    ^~~~~~~~~~~~~~
   sed/execute.c:602:35: error: passing argument 1 of 'setfscreatecon'
   makes pointer from integer without a cast [-Werror=int-conversion]
                  if (setfscreatecon (con) < 0)
                                      ^~~
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:92:1: note: expected 'const char *' but
   argument is of type 'int'
    setfscreatecon (char const *con _GL_UNUSED_PARAMETER)
    ^~~~~~~~~~~~~~
   In file included from ./lib/gettext.h:26:0,
                    from ./basicdefs.h:26,
                    from sed/sed.h:18,
                    from sed/execute.c:20:
   sed/execute.c:603:36: error: format '%s' expects argument of type 'char
   *', but argument 4 has type 'int' [-Werror=format=]
                    fprintf (stderr, _("%s: warning: failed to set
   default" \
                                       ^
   sed/execute.c:603:34: note: in expansion of macro '_'
                    fprintf (stderr, _("%s: warning: failed to set
   default" \
                                     ^
   sed/execute.c:604:64: note: format string is defined here
                                       " file creation context to %s:
   %s"),
                                                                  ~^
                                                                  %d
   sed/execute.c:606:24: error: passing argument 1 of 'freecon' makes
   pointer from integer without a cast [-Werror=int-conversion]
                  freecon (con);
                           ^~~
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:86:1: note: expected 'char *' but argument is
   of type 'int'
    freecon (char *con _GL_UNUSED_PARAMETER) {}
    ^~~~~~~
   sed/execute.c:625:27: error: passing argument 1 of 'setfscreatecon'
   makes pointer from integer without a cast [-Werror=int-conversion]
              setfscreatecon (old_fscreatecon);
                              ^~~~~~~~~~~~~~~
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:92:1: note: expected 'const char *' but
   argument is of type 'int'
    setfscreatecon (char const *con _GL_UNUSED_PARAMETER)
    ^~~~~~~~~~~~~~
   sed/execute.c:626:20: error: passing argument 1 of 'freecon' makes
   pointer from integer without a cast [-Werror=int-conversion]
              freecon (old_fscreatecon);
                       ^~~~~~~~~~~~~~~
   In file included from sed/execute.c:33:0:
   ./lib/selinux/selinux.h:86:1: note: expected 'char *' but argument is
   of type 'int'
    freecon (char *con _GL_UNUSED_PARAMETER) {}
    ^~~~~~~
   cc1: all warnings being treated as errors
   Makefile:2913: recipe for target 'sed/sed_sed-execute.o' failed
   make[2]: *** [sed/sed_sed-execute.o] Error 1
   make[2]: Leaving directory '/tmp/2/sed'
   Makefile:3193: recipe for target 'all-recursive' failed
   make[1]: *** [all-recursive] Error 1
   make[1]: Leaving directory '/tmp/2/sed'
   Makefile:2375: recipe for target 'all' failed
   make: *** [all] Error 2

References

   1. https://www.gnu.org/licenses/gpl.html
   2. http://www.gnu.org/software/sed/
   3. http://www.gnu.org/gethelp/