Re: Extracting written string from the write syscall

Thanks for your replies. However, I am now thinking of another solution. Let's say I can capture write() in the userspace by either instrumenting the LibC or LD_PRELOAD wrapper and store the string buffer passed to write(). Can I call/generate *some other non-instrusive* syscall which can take that string buffer that I stored earlier and that syscall with the buffer will be visible in the audit.log? I am not worried about performance hit right now.

On Thu, Apr 26, 2018 at 7:46 PM Casey Schaufler <casey(a)schaufler-ca.com <mailto:casey@schaufler-ca.com>> wrote: On 4/26/2018 5:08 PM, Sargun Dhillon wrote: > On Thu, Apr 26, 2018 at 4:40 PM, Casey Schaufler <casey(a)schaufler-ca.com <mailto:casey@schaufler-ca.com>> wrote: >> On 4/26/2018 3:57 PM, Steve Grubb wrote: >>> On Thu, 26 Apr 2018 20:34:57 +0000 >>> Wajih Ul Hassan <wajih.lums(a)gmail.com <mailto:wajih.lums@gmail.com>> wrote: >>> >>>> Hi all, >>>>  ..... >> You could write a Linux Security Module (LSM) to monitor the >> content of writes. The performance impact would be rather >> amazing. >> > I would recommend using BPF + kprobes + perf_event buffers for this > purpose. There are enough places you can probe to grab these strings > in the kernel, and if you do your filtering in BPF, you can then push > it into kernel space based on filtering. Although, AFAIK, the BPF JITs > don't do vectorization of instructions, but it's still not too bad. If > you put your kprobe on the syscall itself, and probe the userspace > addr, remember you're going to be open to a time-of-use, time-of-check > style attack. That looks like a whole lot of mechanism to perform a simple task.