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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLES | NOTES | BUGS | AUTHOR | SEE ALSO | COLOPHON |
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seccomp_rule_add(3) libseccomp Documentation seccomp_rule_add(3)
seccomp_rule_add, seccomp_rule_add_exact - Add a seccomp filter
rule
#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.
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). When
adding rules to a filter, it is important to consider the impact
of previously loaded filters; see the seccomp_load(3)
documentation for more information.
All of the filter rules supplied by the calling application are
combined into a union, with additional logic to eliminate
redundant syscall filters. For example, if a rule is added which
allows a given syscall with a specific set of argument values and
later a rule is added which allows the same syscall regardless the
argument values then the first, more specific rule, is effectively
dropped from the filter by the second more generic rule.
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.
If syscall argument comparisons are included in the filter rule,
all of the comparisons must be true for the rule to match.
When adding syscall argument comparisons to the filter it is
important to remember that while it is possible to have multiple
comparisons in a single rule, you can only compare each argument
once in a single rule. In other words, you can not have multiple
comparisons of the 3rd syscall argument in a single rule.
In a filter containing multiple architectures, it is an error to
add a filter rule for a syscall that does not exist in all of the
filter's architectures.
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. It is also important to remember that regardless of the
architectures present in the filter, the syscall numbers used in
filter rules are interpreted in the context of the native
architecture.
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.
SCMP_ACT_NOTIFY
A monitoring process will be notified when a process
running the seccomp filter calls a syscall that matches the
filter rule. The process that invokes the syscall waits in
the kernel until the monitoring process has responded via
seccomp_notify_respond(3) .
When a filter utilizing SCMP_ACT_NOTIFY is loaded into the
kernel, the kernel generates a notification fd that must be
used to communicate between the monitoring process and the
process(es) being filtered. See seccomp_notify_fd(3) for
more information.
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 )
The SCMP_SYS() macro returns a value suitable for use as the
syscall value in the seccomp_rule_add*() functions. In a similar
manner, the SCMP_CMP() and SCMP_A*() macros return values suitable
for use as argument comparisons in the seccomp_rule_add() and
seccomp_rule_add_exact() functions.
The seccomp_rule_add(), seccomp_rule_add_array(),
seccomp_rule_add_exact(), and seccomp_rule_add_exact_array()
functions return zero on success or one of the following error
codes on failure:
-EDOM Architecture specific failure.
-EEXIST
The rule already exists.
-EACCES
The rule conflicts with the filter (for example, the rule
action equals the default action of the filter).
-EFAULT
Internal libseccomp failure.
-EINVAL
Invalid input, either the context or architecture token is
invalid.
-ENOMEM
The library was unable to allocate enough memory.
-EOPNOTSUPP
The library doesn't support the particular operation.
#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;
}
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.
The runtime behavior of seccomp filters is dependent upon the
kernel version, the processor architecture, and other libraries
including libc. This could affect the return code of a seccomp
filter.
* PowerPC glibc will not return a negative number when the
getpid() syscall is invoked. If a seccomp filter has been
created where getpid() will return a negative number from
the kernel, then PowerPC glibc will return the absolute
value of the errno. In this case, it is very difficult for
an application to distinguish between the errno and a valid
pid.
Paul Moore <paul@paul-moore.com>
seccomp_syscall_resolve_name_rewrite(3),
seccomp_syscall_priority(3), seccomp_load(3), seccomp_attr_set(3)
This page is part of the libseccomp (high-level API to the Linux
Kernel's seccomp filter) project. Information about the project
can be found at ⟨https://github.com/seccomp/libseccomp⟩. If you
have a bug report for this manual page, see
⟨https://groups.google.com/d/forum/libseccomp⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/seccomp/libseccomp⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-05-09.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
paul@paul-moore.com 30 May 2020 seccomp_rule_add(3)
Pages that refer to this page: seccomp(2), seccomp_load(3), seccomp_syscall_priority(3), seccomp_syscall_resolve_name(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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