I am trying to run the program to test buffer overflow, but when program crashes it shows me SIGSEGV error as follows:
Program received signal SIGSEGV, Segmentation fault.
0x00000000004006c0 in main (argc=2, argv=0x7fffffffde78)
But the tutorial which I am following is getting the below message:
Program received signal SIGSEGV, Segmentation fault. 0x41414141 in ??
()
Due to this I am not able to get the exact memory location of buffer overflow.
I have already used -fno-stack-protector while compiling my program. because before this I was getting SIGABRT error.
Does anyone have any clue so that i can get in sync with the tutorial.
I was able to figure out the difference in both.
Actually I was trying the same code on Ubuntu 64-bit on virtual box.
But then I tried installing Ubuntu 32-bit on virtual box, so now I am also getting the same message as what was coming in the tutorial.
Also another difference which I noticed in 64 bit and 32-bit OS is that when using 32 bit we can examine the stack using $esp but in 64-bit machine we have to use $rsp
SIGSEGV is the signal raised when your program attempts to access a memory location where it is not supposed to do. Two typical scenarios are:
Deference a non-initialized pointer.
Access an array out-of-bound.
Note, however, even in these two cases, there is no guarantee that SIGSEGV always happen. So don't expect that SIGSEGV message is always the same even with the same code.
Related
This is on Android 12 on a Pixel 6. I am installing a SIGSEGV handler to catch and handle on purpose generated segmentation faults. This works as expected but I am observing a single case where the info->si_addr passed to the handler is not what I expect it to be.
For example let's say that a memory is allocated with mmap at 0x6ecae15000 and size 4194304 bytes. It is protected with PROT_NONE. Then there is a write on address 0x6ecae1e000. A SIGSEGV is triggered and the handler is called but the info->si_addr is 0x277500001a93.
However the ucontext->uc_mcontext.fault_address holds the expected address (0x6ecae1e000).
Any ideas why there's this discrepancy in info->si_addr value? Maybe on arm only ucontext->uc_mcontext.fault_address should be relied upon getting the fault address?
I'm using gdb with bochs-gdb to debug a virtual memory implementation I am writing. Every time an exception 14 (page fault) is thrown gdb breaks on the handler for the exception. Is there any way I can disable this behavior so that gdb doesn't break on x86 exceptions?
You can:
handle SIGSEGV nostop
GDB will not stop for page fault but will still print a message. You can also add noprint.
Source:
"If you don't want GDB to stop for page faults, then issue the command
handle SIGSEGV nostop. GDB will still print a message for every page
fault, but it will not come back to a command prompt." link
After debugging my code I get the following error:
Program received signal SIGSEGV, Segmentation fault.
0xb7d79a67 in fgets () from /lib/i386-linux-gnu/libc.so.6
Can anybody explain to me what this means? It's a project built using CMake and OpenGL.
When a program tries to access memory it has no privileges, the Linux Kernel interrupts the program by sending a signal called SEGSEGV. In your fgets, may be you are exceeding the memory you have allocated for your pointer by inputting too much text. Signals is one way the Linux Kernel communicates with the programs (processes in correct sense). It's kind of exception.
Since, you are dealing with files. It's worth checking if your file actually exists. May be you don't have privileges to read the file and hence getting the error.
/lib/i386-linux-gnu/libc.so.6 is a shared library on your Linux system in which fgets function resides and 0xb7d79a67 is (I guess) main memory address your program doesn't have privileges may be goes beyond the file length.
The segmentation-fault(SEGSEGV) can occur when you access protected memory areas, or the memory areas which are used by other programs and hence your program doesn't have any right to access.
Read these articles for better grasp:
Segmentation fault why?, Debugging segmentation faults
consider the following code in C
int n;
scanf("%d",n)
it gives the error Segmentation fault core dumped in GCC compiler in Linux Mandriva
but the following code
int *p=NULL;
*P=8;
gives only segmentation fault why is that so..?
A core dump is a file containing a dump of the state and memory of a program at the time it crashed. Since core dumps can take non-trivial amounts of disk space, there is a configurable limit on how large they can be. You can see it with ulimit -c.
Now, when you get a segmentation fault, the default action is to terminate the process and dump core. Your shell tells what has happened, if a process has terminated with a segmentation fault signal it will print Segmentation fault, and if that process has additionally dumped core (when the ulimit setting and the permissions on the directory where the core dump is to be generated allow it), it will tell you so.
Assuming you're running both of these on the same system, with the same ulimit -c settings (which would be my first guess as to the difference you're seeing), then its possible the optimizer is "noticing" the clearly undefined behavior in the second example, and generating its own exit. You could check with objdump -x.
In the first case 'n' could have any value, you might own this memory (or not), it might be writeable (or not) but it probably exists. There is no reason that n is necessarily zero.
Writing to NULL is definetly naughty and something the OS is going to notice!
I have the following problem with my C program: Somewhere is a stack overflow. Despite compiling without optimization and with debugger symbols, the program exits with this output (within or outside of gdb on Linux):
Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.
The only way I could detect that this actually is stack overflow was running the program through valgrind. Is there any way I can somehow force the operating system to dump a call stack trace which would help me locate the problem?
Sadly, gdb does not allow me to easily tap into the program either.
If you allow the system to dump core files you can analyze them with gdb:
$ ulimit -c unlimited # bash sentence to allow for infinite sized cores
$ ./stack_overflow
Segmentation fault (core dumped)
$ gdb -c core stack_overflow
gdb> bt
#0 0x0000000000400570 in f ()
#1 0x0000000000400570 in f ()
#2 0x0000000000400570 in f ()
...
Some times I have seen a badly generated core file that had an incorrect stack trace, but in most cases the bt will yield a bunch of recursive calls to the same method.
The core file might have a different name that could include the process id, it depends on the default configuration of the kernel in your current system, but can be controlled with (run as root or with sudo):
$ sysctl kernel.core_uses_pid=1
With GCC you can try this:
-fstack-protector
Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits.
-fstack-protector-all
Like -fstack-protector except that all functions are protected.
http://gcc.gnu.org/onlinedocs/gcc-4.3.3/gcc/Optimize-Options.html#Optimize-Options
When a program dies with SIGSEGV, it normally dumps core on Unix. Could you load that core into debugger and check the state of the stack?