seccomp_rule_add(3) libseccomp Documentation seccomp_rule_add(3)
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 fil-
ter 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 sec-
comp_rule_add_exact() and seccomp_rule_add_exact_array() functions will attempt to add the rule exactly as specified so it may behave dif-
ferently 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 spe-
cific 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 gen-
erated 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)
paul@paul-moore.com 25 July 2012 seccomp_rule_add(3)