[PATCH v11 4/9] samples/landlock: Add quiet flag support to sandboxer
Tingmao Wang
m at maowtm.org
Fri Jun 12 01:48:50 UTC 2026
Adds ability to set which access bits to quiet via LL_*_QUIET_ACCESS (FS,
NET or SCOPED), and attach quiet flags to individual objects via
LL_*_QUIET for FS and NET.
Assisted-by: GitHub-Copilot:claude-opus-4.8 copilot-reviepickw
Signed-off-by: Tingmao Wang <m at maowtm.org>
---
Changes in v11:
- Error if quiet flags not supported by current kernel but quiet envs provided
- Fix comment
- Refactor env vars in sandboxer: LL_{FS,NET,SCOPED}_QUIET_ACCESS are
merged into one LL_QUIET_ACCESS, and used more sensible names.
Changes in v10:
- Remove stray __attribute__((fallthrough)); (Thanks Justin for
spotting)
Changes in v9:
- Add udp connect / bind quiet flag support
Changes in v8:
- Rebase on top of mic/next
- populate_ruleset_net() already does not require the env var to be
present, so remove redundant comment and check above
populate_ruleset_net(ENV_NET_QUIET_NAME, ...).
Changes in v6:
- Make populate_ruleset_{fs,net} take a flags argument instead of a bool
quiet (suggested by Justin Suess)
- Fix if braces style
Changes in v3:
- Minor change to the above commit message.
Changes in v2:
- Added new environment variables to control which quiet access bits to
set on the rule, and populate quiet_access_* from it.
- Added support for quieting net rules and scoped access. Renamed patch
title.
- Increment ABI version
samples/landlock/sandboxer.c | 138 ++++++++++++++++++++++++++++++++---
1 file changed, 127 insertions(+), 11 deletions(-)
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index f44db2857bbf..f18228ccf66a 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -58,9 +58,12 @@ static inline int landlock_restrict_self(const int ruleset_fd,
#define ENV_FS_RO_NAME "LL_FS_RO"
#define ENV_FS_RW_NAME "LL_FS_RW"
+#define ENV_FS_QUIET_NAME "LL_FS_QUIET"
#define ENV_TCP_BIND_NAME "LL_TCP_BIND"
#define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
+#define ENV_NET_QUIET_NAME "LL_NET_QUIET"
#define ENV_SCOPED_NAME "LL_SCOPED"
+#define ENV_QUIET_ACCESS_NAME "LL_QUIET_ACCESS"
#define ENV_FORCE_LOG_NAME "LL_FORCE_LOG"
#define ENV_UDP_BIND_NAME "LL_UDP_BIND"
#define ENV_UDP_CONNECT_SEND_NAME "LL_UDP_CONNECT_SEND"
@@ -119,7 +122,7 @@ static int parse_path(char *env_path, const char ***const path_list)
/* clang-format on */
static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
- const __u64 allowed_access)
+ const __u64 allowed_access, __u32 flags)
{
int num_paths, i, ret = 1;
char *env_path_name;
@@ -169,7 +172,7 @@ static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
if (!S_ISDIR(statbuf.st_mode))
path_beneath.allowed_access &= ACCESS_FILE;
if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
- &path_beneath, 0)) {
+ &path_beneath, flags)) {
fprintf(stderr,
"Failed to update the ruleset with \"%s\": %s\n",
path_list[i], strerror(errno));
@@ -187,7 +190,7 @@ static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
}
static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
- const __u64 allowed_access)
+ const __u64 allowed_access, __u32 flags)
{
int ret = 1;
char *env_port_name, *env_port_name_next, *strport;
@@ -215,7 +218,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
}
net_port.port = port;
if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
- &net_port, 0)) {
+ &net_port, flags)) {
fprintf(stderr,
"Failed to update the ruleset with port \"%llu\": %s\n",
net_port.port, strerror(errno));
@@ -303,6 +306,69 @@ static bool check_ruleset_scope(const char *const env_var,
/* clang-format on */
+/*
+ * Parses ENV_QUIET_ACCESS_NAME and sets the quiet_access_fs,
+ * quiet_access_net and quiet_scoped masks of @ruleset_attr accordingly.
+ */
+static int add_quiet_access(const char *const env_var,
+ struct landlock_ruleset_attr *const ruleset_attr)
+{
+ char *env_quiet_access, *env_quiet_access_next, *str_access;
+
+ env_quiet_access = getenv(env_var);
+ if (!env_quiet_access)
+ return 0;
+
+ env_quiet_access = strdup(env_quiet_access);
+ env_quiet_access_next = env_quiet_access;
+ unsetenv(env_var);
+
+ while ((str_access = strsep(&env_quiet_access_next, ENV_DELIMITER))) {
+ if (strcmp(str_access, "") == 0)
+ continue;
+ else if (strcmp(str_access, "all") == 0) {
+ ruleset_attr->quiet_access_fs =
+ ruleset_attr->handled_access_fs;
+ ruleset_attr->quiet_access_net =
+ ruleset_attr->handled_access_net;
+ ruleset_attr->quiet_scoped = ruleset_attr->scoped;
+ } else if (strcmp(str_access, "read") == 0)
+ ruleset_attr->quiet_access_fs |= ACCESS_FS_ROUGHLY_READ;
+ else if (strcmp(str_access, "write") == 0)
+ ruleset_attr->quiet_access_fs |=
+ ACCESS_FS_ROUGHLY_WRITE;
+ else if (strcmp(str_access, "tcp_bind") == 0)
+ ruleset_attr->quiet_access_net |=
+ LANDLOCK_ACCESS_NET_BIND_TCP;
+ else if (strcmp(str_access, "tcp_connect") == 0)
+ ruleset_attr->quiet_access_net |=
+ LANDLOCK_ACCESS_NET_CONNECT_TCP;
+ else if (strcmp(str_access, "udp_bind") == 0)
+ ruleset_attr->quiet_access_net |=
+ LANDLOCK_ACCESS_NET_BIND_UDP;
+ else if (strcmp(str_access, "udp_connect") == 0)
+ ruleset_attr->quiet_access_net |=
+ LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP;
+ else if (strcmp(str_access, "abstract_unix_socket") == 0)
+ ruleset_attr->quiet_scoped |=
+ LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET;
+ else if (strcmp(str_access, "signal") == 0)
+ ruleset_attr->quiet_scoped |= LANDLOCK_SCOPE_SIGNAL;
+ else {
+ fprintf(stderr, "Unknown quiet access \"%s\"\n",
+ str_access);
+ free(env_quiet_access);
+ return -1;
+ }
+ }
+
+ free(env_quiet_access);
+ ruleset_attr->quiet_access_fs &= ruleset_attr->handled_access_fs;
+ ruleset_attr->quiet_access_net &= ruleset_attr->handled_access_net;
+ ruleset_attr->quiet_scoped &= ruleset_attr->scoped;
+ return 0;
+}
+
#define LANDLOCK_ABI_LAST 10
#define XSTR(s) #s
@@ -337,6 +403,19 @@ static const char help[] =
"\n"
"A sandboxer should not log denied access requests to avoid spamming logs, "
"but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n"
+ ENV_FS_QUIET_NAME " and " ENV_NET_QUIET_NAME ", both optional, can then be used "
+ "to make access to some denied paths or network ports not trigger audit logging.\n"
+ ENV_QUIET_ACCESS_NAME " can be used to specify which accesses should be quieted "
+ "(required when " ENV_FS_QUIET_NAME " or " ENV_NET_QUIET_NAME " is set):\n"
+ " - \"all\" to quiet all of the accesses below\n"
+ " - \"read\" to quiet all file/dir read accesses\n"
+ " - \"write\" to quiet all file/dir write accesses\n"
+ " - \"tcp_bind\" to quiet tcp bind denials\n"
+ " - \"tcp_connect\" to quiet tcp connect denials\n"
+ " - \"udp_bind\" to quiet udp bind denials\n"
+ " - \"udp_connect\" to quiet udp connect / send denials\n"
+ " - \"abstract_unix_socket\" to quiet abstract unix socket denials\n"
+ " - \"signal\" to quiet signal denials\n"
"\n"
"Example:\n"
ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
@@ -369,7 +448,11 @@ int main(const int argc, char *const argv[], char *const *const envp)
LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP,
.scoped = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
LANDLOCK_SCOPE_SIGNAL,
+ .quiet_access_fs = 0,
+ .quiet_access_net = 0,
+ .quiet_scoped = 0,
};
+ bool quiet_supported = true;
int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
int set_restrict_flags = 0;
@@ -460,6 +543,8 @@ int main(const int argc, char *const argv[], char *const *const envp)
ruleset_attr.handled_access_net &=
~(LANDLOCK_ACCESS_NET_BIND_UDP |
LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP);
+ /* Removes quiet flags for ABI < 10 later on. */
+ quiet_supported = false;
/* Must be printed for any ABI < LANDLOCK_ABI_LAST. */
fprintf(stderr,
@@ -526,6 +611,25 @@ int main(const int argc, char *const argv[], char *const *const envp)
unsetenv(ENV_FORCE_LOG_NAME);
}
+ /* Set the quiet access masks. */
+ if (quiet_supported) {
+ if ((getenv(ENV_FS_QUIET_NAME) || getenv(ENV_NET_QUIET_NAME)) &&
+ !getenv(ENV_QUIET_ACCESS_NAME)) {
+ fprintf(stderr,
+ "%s must be set (e.g. to \"all\") when %s or %s is used\n",
+ ENV_QUIET_ACCESS_NAME, ENV_FS_QUIET_NAME,
+ ENV_NET_QUIET_NAME);
+ return 1;
+ }
+ if (add_quiet_access(ENV_QUIET_ACCESS_NAME, &ruleset_attr))
+ return 1;
+ } else if (getenv(ENV_FS_QUIET_NAME) || getenv(ENV_NET_QUIET_NAME) ||
+ getenv(ENV_QUIET_ACCESS_NAME)) {
+ fprintf(stderr,
+ "Quiet flags not supported by current kernel\n");
+ return 1;
+ }
+
ruleset_fd =
landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
if (ruleset_fd < 0) {
@@ -533,30 +637,42 @@ int main(const int argc, char *const argv[], char *const *const envp)
return 1;
}
- if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
+ if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro, 0))
goto err_close_ruleset;
- }
- if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
+ if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw, 0))
goto err_close_ruleset;
+
+ /* Don't require this env to be present. */
+ if (quiet_supported && getenv(ENV_FS_QUIET_NAME)) {
+ if (populate_ruleset_fs(ENV_FS_QUIET_NAME, ruleset_fd, 0,
+ LANDLOCK_ADD_RULE_QUIET))
+ goto err_close_ruleset;
}
if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
- LANDLOCK_ACCESS_NET_BIND_TCP)) {
+ LANDLOCK_ACCESS_NET_BIND_TCP, 0)) {
goto err_close_ruleset;
}
if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
- LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
+ LANDLOCK_ACCESS_NET_CONNECT_TCP, 0)) {
goto err_close_ruleset;
}
if (populate_ruleset_net(ENV_UDP_BIND_NAME, ruleset_fd,
- LANDLOCK_ACCESS_NET_BIND_UDP)) {
+ LANDLOCK_ACCESS_NET_BIND_UDP, 0)) {
goto err_close_ruleset;
}
if (populate_ruleset_net(ENV_UDP_CONNECT_SEND_NAME, ruleset_fd,
- LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP)) {
+ LANDLOCK_ACCESS_NET_CONNECT_SEND_UDP, 0)) {
goto err_close_ruleset;
}
+ if (quiet_supported) {
+ if (populate_ruleset_net(ENV_NET_QUIET_NAME, ruleset_fd, 0,
+ LANDLOCK_ADD_RULE_QUIET)) {
+ goto err_close_ruleset;
+ }
+ }
+
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
perror("Failed to restrict privileges");
goto err_close_ruleset;
--
2.54.0
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