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Date: Sun, 15 Apr 2012 09:20:07 -0700
From: Kees Cook <keescook@...omium.org>
To: David Windsor <dwindsor@...il.com>
Cc: Paul Moore <paul@...l-moore.com>,
libseccomp-discuss@...ts.sourceforge.net,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
Will Drewry <wad@...omium.org>
Subject: Re: ANN: libseccomp
Hi,
The seccomp mini-tutorial I wrote[1] could be extended to restart
system calls. That's the closest I've seen so far. Right now it just
needs to be run repeatedly until all the needed syscalls are found. :P
-Kees
[1] http://outflux.net/teach-seccomp/
On Sat, Apr 14, 2012 at 7:10 AM, David Windsor <dwindsor@...il.com> wrote:
> Out of curiosity, are there any current efforts towards creating a "learning
> mode" type of application for seccomp? I.e. creating a profile for a
> particular application based upon which syscalls it makes during normal
> operation. I realize that many people consider this a security
> anti-pattern, but it could be useful for the initial creation of a seccomp
> filter for a particular application, and other security subsystems already
> do this (ala AppArmor's learning/complain mode). IIUC, no other kernel
> mechanisms would need to be created; ptrace could accomplish syscall
> monitoring.
>
> Thanks,
> David Windsor
>
> On Mon, Apr 9, 2012 at 2:58 PM, Paul Moore <paul@...l-moore.com> wrote:
>>
>> With the seccomp patches finally stabilizing a bit, it seems like now is a
>> good time to announce libseccomp: a library designed to make it easier to
>> create complex, architecture independent seccomp filters.
>>
>> * http://sourceforge.net/projects/libseccomp/
>> * git clone git://git.code.sf.net/p/libseccomp/libseccomp
>>
>> The library has only been in development for the past couple months, so it
>> may
>> be a little rough around the edges, and definitely could use more testing,
>> but
>> it is functional and has had some basic testing against the seccomp v17
>> patches. The project currently lacks any online documentation or a
>> website
>> beyond the basic SF.net tools, but there are current man pages in the
>> source
>> repository and the code is reasonably well commented.
>>
>> For those of you who are interested in making use of the library, or
>> contributing to its development and testing, we do have a mailing list
>> setup
>> (see the To/CC line above) and you can subscribe at the link below; all
>> are
>> welcome.
>>
>> * https://lists.sourceforge.net/lists/listinfo/libseccomp-discuss
>>
>> To demonstrate some of the basic libseccomp capabilities, I've included a
>> short example below. The example is trivial, it opens /dev/zero and
>> writes to
>> /dev/null, but it shows how to use libseccomp to create a simple filter
>> and
>> load it into the kernel; filtering both on just the syscall and a syscall
>> with
>> specific arguments.
>>
>> > #include <errno.h>
>> > #include <stdlib.h>
>> > #include <stdio.h>
>> > #include <unistd.h>
>> >
>> > #include <seccomp.h>
>> >
>> > #define BUF_LEN 256
>> >
>> > int main(int argc, char *argv[])
>> > {
>> > int rc;
>> > FILE *read_stream, *write_stream;
>> > unsigned char buf[BUF_LEN];
>> > size_t op_len;
>> >
>> > /* initialize the seccomp filter */
>> > printf("scmp: initializing the seccomp filter ...");
>> > rc = seccomp_init(SCMP_ACT_KILL);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > printf("ok\n");
>> >
>> > /* do the setup */
>> > printf("info: opening /dev/zero for reading ... ");
>> > read_stream = fopen("/dev/zero", "r");
>> > if (read_stream == NULL)
>> > goto failure;
>> > printf("ok\n");
>> > printf("info: opening /dev/null for writing ... ");
>> > write_stream = fopen("/dev/null", "w");
>> > if (write_stream == NULL)
>> > goto failure;
>> > printf("ok\n");
>> >
>> > /* configure the seccomp filter */
>> > printf("scmp: configuring the seccomp_filter ... ");
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(read), 1,
>> > SCMP_A0(SCMP_CMP_EQ, fileno(read_stream)));
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
>> > SCMP_A0(SCMP_CMP_EQ, STDOUT_FILENO));
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
>> > SCMP_A0(SCMP_CMP_EQ, STDERR_FILENO));
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
>> > SCMP_A0(SCMP_CMP_EQ, fileno(write_stream)));
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(fstat), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(mmap), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(mprotect), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > rc = seccomp_rule_add(SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0);
>> > if (rc < 0)
>> > goto failure_scmp;
>> > printf("ok\n");
>> >
>> > /* load the seccomp filter into the kernel */
>> > printf("scmp: load the filter ... ");
>> > rc = seccomp_load();
>> > if (rc < 0)
>> > goto failure_scmp;
>> > seccomp_release();
>> > printf("ok\n");
>> >
>> > /* perform the i/o */
>> > printf("info: attempting to read BUF_LEN bytes ... ");
>> > op_len = fread(buf, BUF_LEN, 1, read_stream);
>> > if (op_len != 1)
>> > return errno;
>> > printf("ok\n");
>> >
>> > printf("info: attempting to write BUF_LEN bytes ... ");
>> > op_len = fwrite(buf, BUF_LEN, 1, write_stream);
>> > if (op_len != 1)
>> > return errno;
>> > printf("ok\n");
>> >
>> > /* shutdown */
>> > printf("info: closing file streams and exiting\n");
>> > fclose(write_stream);
>> > fclose(read_stream);
>> > return 0;
>> >
>> > failure_scmp:
>> > errno = -rc;
>> > failure:
>> > /* oops ... */
>> > printf("failed, errno = %u\n", errno);
>> > return errno;
>> > }
>>
>> --
>> paul moore
>> www.paul-moore.com
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe
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>
>
>
>
> --
> PGP: 6141 5FFD 11AE 9844 153E F268 7C98 7268 6B19 6CC9
--
Kees Cook
ChromeOS Security
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