Provided by: libseccomp-dev_2.1.1-1ubuntu1~trusty5_amd64 
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, ...);
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. 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() and SCMP_A{0-5}() macros generate a scmp_arg_cmp structure for use with the
above functions. The SCMP_CMP() macro allows the caller to specify an arbitrary argument
along with the comparison operator, mask, and datum values where the SCMP_A{0-5}() macros
are specific to a certain argument. See the EXAMPLES section below.
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.
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 process will be killed by the kernel when it calls a syscall that does not
match any of the configured seccomp filter rules.
SCMP_ACT_TRAP
The process will throw a SIGSYS signal when it calls a syscall that does not match
any of the configured seccomp filter rules.
SCMP_ACT_ERRNO(uint16_t errno)
The process will receive a return value of errno when it calls a syscall that does
not match any of the configured seccomp filter rules.
SCMP_ACT_TRACE(uint16_t msg_num)
If the process 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_ALLOW
The seccomp filter will have no effect on the process calling the syscall if it
does not match any of the configured seccomp filter rules.
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>
#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(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 http://libseccomp.sf.net. This 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_priority(3), seccomp_load(3)