Provided by: libseccomp-dev_2.4.1-0ubuntu0.19.10.3_amd64 bug

NAME

       seccomp_rule_add, seccomp_rule_add_exact - Add a seccomp filter rule

SYNOPSIS

       #include <seccomp.h>

       typedef void * scmp_filter_ctx;

       int SCMP_SYS(syscall_name);

       struct scmp_arg_cmp SCMP_CMP(unsigned int arg,
                                    enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A0(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A1(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A2(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A3(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A4(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A5(enum scmp_compare op, ...);

       struct scmp_arg_cmp SCMP_CMP64(unsigned int arg,
                                    enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A0_64(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A1_64(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A2_64(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A3_64(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A4_64(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A5_64(enum scmp_compare op, ...);

       struct scmp_arg_cmp SCMP_CMP32(unsigned int arg,
                                    enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A0_32(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A1_32(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A2_32(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A3_32(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A4_32(enum scmp_compare op, ...);
       struct scmp_arg_cmp SCMP_A5_32(enum scmp_compare op, ...);

       int seccomp_rule_add(scmp_filter_ctx ctx, uint32_t action,
                            int syscall, unsigned int arg_cnt, ...);
       int seccomp_rule_add_exact(scmp_filter_ctx ctx, uint32_t action,
                                  int syscall, unsigned int arg_cnt, ...);

       int seccomp_rule_add_array(scmp_filter_ctx ctx,
                                  uint32_t action, int syscall,
                                  unsigned int arg_cnt,
                                  const struct scmp_arg_cmp *arg_array);
       int seccomp_rule_add_exact_array(scmp_filter_ctx ctx,
                                        uint32_t action, int syscall,
                                        unsigned int arg_cnt,
                                        const struct scmp_arg_cmp *arg_array);

       Link with -lseccomp.

DESCRIPTION

       The    seccomp_rule_add(),    seccomp_rule_add_array(),    seccomp_rule_add_exact(),   and
       seccomp_rule_add_exact_array() functions all add a new filter rule to the current  seccomp
       filter.   The  seccomp_rule_add() and seccomp_rule_add_array() functions will make a "best
       effort" to add the rule as specified, but may alter the rule slightly due to  architecture
       specifics  (e.g. internal rewriting of multiplexed syscalls, like socket and ipc functions
       on x86).  The seccomp_rule_add_exact() and seccomp_rule_add_exact_array()  functions  will
       attempt  to  add  the  rule exactly as specified so it may behave differently on different
       architectures.  While it does not guarantee a exact filter ruleset, seccomp_rule_add() and
       seccomp_rule_add_array() do guarantee the same behavior regardless of the architecture.

       The  newly  added  filter rule does not take effect until the entire filter is loaded into
       the kernel using seccomp_load(3).

       The SCMP_CMP(),  SCMP_CMP64(),  SCMP_A{0-5}(),  and  SCMP_A{0-5}_64()  macros  generate  a
       scmp_arg_cmp  structure  for use with the above functions. The SCMP_CMP() and SCMP_CMP64()
       macros allows the caller to specify  an  arbitrary  argument  along  with  the  comparison
       operator,   64-bit   mask,   and   64-bit   datum   values  where  the  SCMP_A{0-5}()  and
       SCMP_A{0-5}_64() macros are specific to a certain argument.

       The SCMP_CMP32() and SCMP_A{0-5}_32() macros are similar to the variants above,  but  they
       take 32-bit mask and 32-bit datum values.

       It  is  recommended  that  whenever  possible  developers  avoid  using the SCMP_CMP() and
       SCMP_A{0-5}() macros and use the variants which are explicitly 32 or 64-bit.  This  should
       help eliminate problems caused by an unwanted sign extension of negative datum values.

       While it is possible to specify the syscall value directly using the standard __NR_syscall
       values, in order to ensure proper operation across multiple  architectures  it  is  highly
       recommended to use the SCMP_SYS() macro instead.  See the EXAMPLES section below.

       Starting  with Linux v4.8, there may be a need to create a rule with a syscall value of -1
       to allow tracing programs to skip a syscall invocation; in order to create a rule  with  a
       -1  syscall  value  it is necessary to first set the SCMP_FLTATR_API_TSKIP attribute.  See
       seccomp_attr_set(3) for more information.

       The filter context ctx is the value returned by the call to seccomp_init(3).

       Valid action values are as follows:

       SCMP_ACT_KILL
              The thread will be killed by the kernel when it calls a syscall  that  matches  the
              filter rule.

       SCMP_ACT_KILL_PROCESS
              The  process  will be killed by the kernel when it calls a syscall that matches the
              filter rule.

       SCMP_ACT_TRAP
              The thread will throw a SIGSYS signal when it calls  a  syscall  that  matches  the
              filter rule.

       SCMP_ACT_ERRNO(uint16_t errno)
              The  thread  will  receive  a  return  value  of errno when it calls a syscall that
              matches the filter rule.

       SCMP_ACT_TRACE(uint16_t msg_num)
              If  the  thread  is  being  traced  and   the   tracing   process   specified   the
              PTRACE_O_TRACESECCOMP  option in the call to ptrace(2), the tracing process will be
              notified, via PTRACE_EVENT_SECCOMP , and the  value  provided  in  msg_num  can  be
              retrieved using the PTRACE_GETEVENTMSG option.

       SCMP_ACT_LOG
              The  seccomp  filter  will  have  no effect on the thread calling the syscall if it
              matches the filter rule but the syscall will be logged.

       SCMP_ACT_ALLOW
              The seccomp filter will have no effect on the thread  calling  the  syscall  if  it
              matches the filter rule.

       Valid comparison op values are as follows:

       SCMP_CMP_NE
              Matches when the argument value is not equal to the datum value, example:

              SCMP_CMP( arg , SCMP_CMP_NE , datum )

       SCMP_CMP_LT
              Matches when the argument value is less than the datum value, example:

              SCMP_CMP( arg , SCMP_CMP_LT , datum )

       SCMP_CMP_LE
              Matches when the argument value is less than or equal to the datum value, example:

              SCMP_CMP( arg , SCMP_CMP_LE , datum )

       SCMP_CMP_EQ
              Matches when the argument value is equal to the datum value, example:

              SCMP_CMP( arg , SCMP_CMP_EQ , datum )

       SCMP_CMP_GE
              Matches  when  the  argument  value  is  greater  than or equal to the datum value,
              example:

              SCMP_CMP( arg , SCMP_CMP_GE , datum )

       SCMP_CMP_GT
              Matches when the argument value is greater than the datum value, example:

              SCMP_CMP( arg , SCMP_CMP_GT , datum )

       SCMP_CMP_MASKED_EQ
              Matches when the masked argument value is equal to the masked datum value, example:

              SCMP_CMP( arg , SCMP_CMP_MASKED_EQ , mask , datum )

RETURN VALUE

       The   seccomp_rule_add(),    seccomp_rule_add_array(),    seccomp_rule_add_exact(),    and
       seccomp_rule_add_exact_array()  functions return zero on success, negative errno values on
       failure.

EXAMPLES

       #include <fcntl.h>
       #include <seccomp.h>
       #include <sys/stat.h>
       #include <sys/types.h>
       #include <stddef.h>

       #define BUF_SIZE    256

       int main(int argc, char *argv[])
       {
            int rc = -1;
            scmp_filter_ctx ctx;
            struct scmp_arg_cmp arg_cmp[] = { SCMP_A0(SCMP_CMP_EQ, 2) };
            int fd;
            unsigned char buf[BUF_SIZE];

            ctx = seccomp_init(SCMP_ACT_KILL);
            if (ctx == NULL)
                 goto out;

            /* ... */

            fd = open("file.txt", 0);

            /* ... */

            rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
            if (rc < 0)
                 goto out;

            rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);
            if (rc < 0)
                 goto out;

            rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit), 0);
            if (rc < 0)
                 goto out;

            rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 3,
                            SCMP_A0(SCMP_CMP_EQ, fd),
                            SCMP_A1(SCMP_CMP_EQ, (scmp_datum_t)buf),
                            SCMP_A2(SCMP_CMP_LE, BUF_SIZE));
            if (rc < 0)
                 goto out;

            rc = seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
                            SCMP_CMP(0, SCMP_CMP_EQ, fd));
            if (rc < 0)
                 goto out;

            rc = seccomp_rule_add_array(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 1,
                                  arg_cmp);
            if (rc < 0)
                 goto out;

            rc = seccomp_load(ctx);
            if (rc < 0)
                 goto out;

            /* ... */

       out:
            seccomp_release(ctx);
            return -rc;
       }

NOTES

       While the seccomp filter can be generated independent of the  kernel,  kernel  support  is
       required to load and enforce the seccomp filter generated by libseccomp.

       The  libseccomp project site, with more information and the source code repository, can be
       found at https://github.com/seccomp/libseccomp.  This tool,  as  well  as  the  libseccomp
       library,  is  currently  under  development, please report any bugs at the project site or
       directly to the author.

AUTHOR

       Paul Moore <paul@paul-moore.com>

SEE ALSO

       seccomp_syscall_resolve_name_rewrite(3),   seccomp_syscall_priority(3),   seccomp_load(3),
       seccomp_attr_set(3)