These two factors limit the cases in which system is useable. On Linux, this is especially well optimized, and about as cheap as creating a pthread. Both parent and child processes can then run concurrently and communicate quite easily. The original program exits invisibly and the new process takes over. When then new process returns, it will return to whatever called the original process, as if that process had returned at that point instead of vanishing. For example, at a certain point, a program could use system to invoke a text editor to edit some configuration file.
It need not concern itself too much with what happens, but it should certainly wait until the user has saved and closed the editor before continuing. It can then use the return value to find out if the editing session was successful, in the sense that the editor actually opened the requested file and that the editor itself existed at all! Because not all OS's use the whole return value. In this case, it's truncated to the low 8 bits. Note that when the shell or whatever runs your program , it does not jump straight to your main , but some other functionality is performed first to initialize things that are needed by your main function.
Exactly how this works is dependent on several things:. Next make sure you are compiling the test program without stack smashing protection and set the memory execution bit. Compile it with the following gcc options to accomplish -fno-stack-protector -z execstack.
Also I found I needed more space to actually execute a shell so I would change your buffer to something more like buffer[64]. Next you can run the app in gdb and get the stack address you need to return to First set a breakpoint right after the strcpy.
Next determine your max buffer size. I know that the buffer of 64 crashes at 72 bytes so I will just go from that..
You could use something like metasploits pattern methods to give you this or just figure it out from trial and error running the app to find out the exact byte count it takes before getting a segfault or make up a pattern of your own and match the rip address like you would with the metasploit pattern option. Next, there are many different ways to get the payload you need but since we are running a 64bit app, we will use a 64bit payload.
I compiled C and then grabbed the ASM from gdb and then made some changes to remove the x00 chars by changing the mov instructions to xor for the null values and then shl and shr to remove them from the shell command.
We will show this later but for now the payload is as follows. We can pad the payload with x90 nop so that instruction will not be interrupted. Ill add 2 at the end of the payload and 22 at the beginning. Also I will tack on the return address that we want to the end in reverse giving the following.. Now if you want to run it outside of gdb, you may have to fudge with the return address. In my case the address becomes x70xe0xffxffxffx7f outside of gdb.
I just increased it until it worked by going to 40 then 50 then 60 then The compiler is reserving the stack space for the MemBlock instance on each call to foo , regardless of the control flow within foo. This is a common optimisation to prevent having to repeatedly adjust the stack pointer within the function.
Instead, the compiler calculates the maximum stack space required and on entry to the function adjusts the stack pointer by that amount. As you've observed, this results in losing stack space reserved for objects you don't actually use. The answer is to not do that; if you're only using some large-footprint objects within certain branches then separate those branches out into their own function. Incidentally, this is why archaic versions of C required all function-scope variables to be declared at the top of the function; so that the compiler can easily work out how much stack space the function requires.
Asked 2 Months ago Answers: 5 Viewed 29 times. Personally, I make a distinction: A buffer overflow is when you try to put more items in the array than the array can hold. David Miani. Only authorized users can answer the question.
Viewed 68k times. Queries Why binding redirect shows only major version and not minor, build and revision numbers? Does old and new version change only when there is change in major version? Improve this question. Nikhil Agrawal. Nikhil Agrawal Nikhil Agrawal It can be any version, not just the major one.
Evk: All the examples that I have see show major version only. Well those are just examples, and it is nowhere stated that it's the only way possible. Add a comment. Active Oldest Votes. You can redirect any versions of libraries, not just major ones. Improve this answer.
Little Endian 6 6 silver badges 18 18 bronze badges. Evk Evk What file and under what section do these go into? Can someone please provide a link to source like MSDN or similar for reference? I had a coworker tell me to "just add an assembly redirect to your exe file" right before going on vacation for a week and I landed here and while this answer looks great it's lacking context and reference. AlexanderDerck in config file of application A - they have no effect as far as I'm aware in config files of libraries, except maybe when this library is unit test library and is "executed" in some sense by unit test runner.
AlexanderDerck there was a question couple of weeks ago, with many upvotes and even bounty, which was asking exactly that, but no one was able to provide convincing answer - stackoverflow.
CodeEngine publicKeyToken identifies assembly C. Only signed assemblies have that public key token identifying them. Here is a related question about how you can find out that token given that you have assembly: stackoverflow. PaulMcCarthy I think. NET team knows it's rubbish. Thankfully they didn't bring this "feature" to. NET Core. Show 15 more comments. Version The result of above is. Major Minor Build Revision 9 0 0 0 See References: How can i see the assembly version of a.
Amyth Amyth 1, 7 7 silver badges 13 13 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.
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