Break the read and write paths of the kernel.seccomp.actions_logged sysctl into separate functions to maintain readability. An upcoming change will need to audit writes, but not reads, of this sysctl which would introduce too many conditional code paths on whether or not the 'write' parameter evaluates to true. Signed-off-by: Tyler Hicks <tyhicks(a)canonical.com&gt; --- kernel/seccomp.c | 60 +++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 38 insertions(+), 22 deletions(-) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index dc77548..f4afe67 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1199,48 +1199,64 @@ static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names) return true; } -static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, - void __user *buffer, size_t *lenp, - loff_t *ppos) +static int read_actions_logged(struct ctl_table *ro_table, void __user *buffer, + size_t *lenp, loff_t *ppos) { char names[sizeof(seccomp_actions_avail)]; struct ctl_table table; + + memset(names, 0, sizeof(names)); + + if (!seccomp_names_from_actions_logged(names, sizeof(names), + seccomp_actions_logged)) + return -EINVAL; + + table = *ro_table; + table.data = names; + table.maxlen = sizeof(names); + return proc_dostring(&table, 0, buffer, lenp, ppos); +} + +static int write_actions_logged(struct ctl_table *ro_table, void __user *buffer, + size_t *lenp, loff_t *ppos) +{ + char names[sizeof(seccomp_actions_avail)]; + struct ctl_table table; + u32 actions_logged; int ret; - if (write && !capable(CAP_SYS_ADMIN)) + if (!capable(CAP_SYS_ADMIN)) return -EPERM; memset(names, 0, sizeof(names)); - if (!write) { - if (!seccomp_names_from_actions_logged(names, sizeof(names), - seccomp_actions_logged)) - return -EINVAL; - } - table = *ro_table; table.data = names; table.maxlen = sizeof(names); - ret = proc_dostring(&table, write, buffer, lenp, ppos); + ret = proc_dostring(&table, 1, buffer, lenp, ppos); if (ret) return ret; - if (write) { - u32 actions_logged; - - if (!seccomp_actions_logged_from_names(&actions_logged, - table.data)) - return -EINVAL; - - if (actions_logged & SECCOMP_LOG_ALLOW) - return -EINVAL; + if (!seccomp_actions_logged_from_names(&actions_logged, table.data)) + return -EINVAL; - seccomp_actions_logged = actions_logged; - } + if (actions_logged & SECCOMP_LOG_ALLOW) + return -EINVAL; + seccomp_actions_logged = actions_logged; return 0; } +static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + if (write) + return write_actions_logged(ro_table, buffer, lenp, ppos); + else + return read_actions_logged(ro_table, buffer, lenp, ppos); +} + static struct ctl_path seccomp_sysctl_path[] = { { .procname = "kernel", }, { .procname = "seccomp", }, -- 2.7.4

The function that converts a bitmask of seccomp actions that are allowed to be logged is currently only used for constructing the display string for the kernel.seccomp.actions_logged sysctl. That string wants a space character to be used for the separator between actions. A future patch will make use of the same function for building a string that will be sent to the audit subsystem for tracking modifications to the kernel.seccomp.actions_logged sysctl. That string will need to use a comma as a separator. This patch allows the separator character to be configurable to meet both needs. Signed-off-by: Tyler Hicks <tyhicks(a)canonical.com&gt; --- kernel/seccomp.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index f4afe67..b36ac1e 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1135,10 +1135,11 @@ static const struct seccomp_log_name seccomp_log_names[] = { }; static bool seccomp_names_from_actions_logged(char *names, size_t size, - u32 actions_logged) + u32 actions_logged, + const char *sep) { const struct seccomp_log_name *cur; - bool append_space = false; + bool append_sep = false; for (cur = seccomp_log_names; cur->name && size; cur++) { ssize_t ret; @@ -1146,15 +1147,15 @@ static bool seccomp_names_from_actions_logged(char *names, size_t size, if (!(actions_logged & cur->log)) continue; - if (append_space) { - ret = strscpy(names, " ", size); + if (append_sep) { + ret = strscpy(names, sep, size); if (ret < 0) return false; names += ret; size -= ret; } else - append_space = true; + append_sep = true; ret = strscpy(names, cur->name, size); if (ret < 0) @@ -1208,7 +1209,7 @@ static int read_actions_logged(struct ctl_table *ro_table, void __user *buffer, memset(names, 0, sizeof(names)); if (!seccomp_names_from_actions_logged(names, sizeof(names), - seccomp_actions_logged)) + seccomp_actions_logged, " ")) return -EINVAL; table = *ro_table; -- 2.7.4

The decision to log a seccomp action will always be subject to the value of the kernel.seccomp.actions_logged sysctl, even for processes that are being inspected via the audit subsystem, in an upcoming patch. Therefore, we need to emit an audit record on attempts at writing to the actions_logged sysctl when auditing is enabled. This patch updates the write handler for the actions_logged sysctl to emit an audit record on attempts to write to the sysctl. Successful writes to the sysctl will result in a record that includes a normalized list of logged actions in the "actions" field and a "res" field equal to 0. Unsuccessful writes to the sysctl will result in a record that doesn't include the "actions" field and has a "res" field equal to 1. Not all unsuccessful writes to the sysctl are audited. For example, an audit record will not be emitted if an unprivileged process attempts to open the sysctl file for reading since that access control check is not part of the sysctl's write handler. Below are some example audit records when writing various strings to the actions_logged sysctl. Writing "not-a-real-action", when the kernel.seccomp.actions_logged sysctl previously was "kill_process kill_thread trap errno trace log", emits this audit record: type=CONFIG_CHANGE msg=audit(1525275273.537:130): op=seccomp-logging old-actions=kill_process,kill_thread,trap,errno,trace,log res=0 If you then write "kill_process kill_thread errno trace log", this audit record is emitted: type=CONFIG_CHANGE msg=audit(1525275310.208:136): op=seccomp-logging actions=kill_process,kill_thread,errno,trace,log old-actions=kill_process,kill_thread,trap,errno,trace,log res=1 If you then write the string "log log errno trace kill_process kill_thread", which is unordered and contains the log action twice, it results in the same actions value as the previous record: type=CONFIG_CHANGE msg=audit(1525275325.613:142): op=seccomp-logging actions=kill_process,kill_thread,errno,trace,log old-actions=kill_process,kill_thread,errno,trace,log res=1 No audit records are generated when reading the actions_logged sysctl. Suggested-by: Steve Grubb <sgrubb(a)redhat.com&gt; Signed-off-by: Tyler Hicks <tyhicks(a)canonical.com&gt; --- include/linux/audit.h | 5 +++++ kernel/auditsc.c | 25 +++++++++++++++++++++++++ kernel/seccomp.c | 51 ++++++++++++++++++++++++++++++++++++++++++--------- 3 files changed, 72 insertions(+), 9 deletions(-) diff --git a/include/linux/audit.h b/include/linux/audit.h index 75d5b03..d4e35e7 100644 --- a/include/linux/audit.h +++ b/include/linux/audit.h @@ -233,6 +233,8 @@ extern void __audit_inode_child(struct inode *parent, const struct dentry *dentry, const unsigned char type); extern void __audit_seccomp(unsigned long syscall, long signr, int code); +extern void audit_seccomp_actions_logged(const char *names, + const char *old_names, int res); extern void __audit_ptrace(struct task_struct *t); static inline bool audit_dummy_context(void) @@ -502,6 +504,9 @@ static inline void __audit_seccomp(unsigned long syscall, long signr, int code) { } static inline void audit_seccomp(unsigned long syscall, long signr, int code) { } +static inline void audit_seccomp_actions_logged(const char *names, + const char *old_names, int res) +{ } static inline int auditsc_get_stamp(struct audit_context *ctx, struct timespec64 *t, unsigned int *serial) { diff --git a/kernel/auditsc.c b/kernel/auditsc.c index 4e0a4ac..5a0b770 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -2478,6 +2478,31 @@ void __audit_seccomp(unsigned long syscall, long signr, int code) audit_log_end(ab); } +void audit_seccomp_actions_logged(const char *names, const char *old_names, + int res) +{ + struct audit_buffer *ab; + + if (!audit_enabled) + return; + + ab = audit_log_start(current->audit_context, GFP_KERNEL, + AUDIT_CONFIG_CHANGE); + if (unlikely(!ab)) + return; + + audit_log_format(ab, "op=seccomp-logging"); + + if (names) + audit_log_format(ab, " actions=%s", names); + + if (old_names) + audit_log_format(ab, " old-actions=%s", old_names); + + audit_log_format(ab, " res=%d", res); + audit_log_end(ab); +} + struct list_head *audit_killed_trees(void) { struct audit_context *ctx = current->audit_context; diff --git a/kernel/seccomp.c b/kernel/seccomp.c index b36ac1e..da78835 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1219,11 +1219,10 @@ static int read_actions_logged(struct ctl_table *ro_table, void __user *buffer, } static int write_actions_logged(struct ctl_table *ro_table, void __user *buffer, - size_t *lenp, loff_t *ppos) + size_t *lenp, loff_t *ppos, u32 *actions_logged) { char names[sizeof(seccomp_actions_avail)]; struct ctl_table table; - u32 actions_logged; int ret; if (!capable(CAP_SYS_ADMIN)) @@ -1238,24 +1237,58 @@ static int write_actions_logged(struct ctl_table *ro_table, void __user *buffer, if (ret) return ret; - if (!seccomp_actions_logged_from_names(&actions_logged, table.data)) + if (!seccomp_actions_logged_from_names(actions_logged, table.data)) return -EINVAL; - if (actions_logged & SECCOMP_LOG_ALLOW) + if (*actions_logged & SECCOMP_LOG_ALLOW) return -EINVAL; - seccomp_actions_logged = actions_logged; + seccomp_actions_logged = *actions_logged; return 0; } +static void audit_actions_logged(u32 actions_logged, u32 old_actions_logged, + int ret) +{ + char names[sizeof(seccomp_actions_avail)]; + char old_names[sizeof(seccomp_actions_avail)]; + const char *new = names; + const char *old = old_names; + + if (!audit_enabled) + return; + + memset(names, 0, sizeof(names)); + memset(old_names, 0, sizeof(old_names)); + + if (ret || !seccomp_names_from_actions_logged(names, sizeof(names), + actions_logged, ",")) + new = NULL; + + if (!seccomp_names_from_actions_logged(old_names, sizeof(old_names), + old_actions_logged, ",")) + old = NULL; + + return audit_seccomp_actions_logged(new, old, !ret); +} + static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { - if (write) - return write_actions_logged(ro_table, buffer, lenp, ppos); - else - return read_actions_logged(ro_table, buffer, lenp, ppos); + int ret; + + if (write) { + u32 actions_logged = 0; + u32 old_actions_logged = seccomp_actions_logged; + + ret = write_actions_logged(ro_table, buffer, lenp, ppos, + &actions_logged); + audit_actions_logged(actions_logged, old_actions_logged, ret); + } else + ret = read_actions_logged(ro_table, buffer, lenp, ppos); + + return ret; } static struct ctl_path seccomp_sysctl_path[] = { -- 2.7.4

Seccomp logging for "handled" actions such as RET_TRAP, RET_TRACE, or RET_ERRNO can be very noisy for processes that are being audited. This patch modifies the seccomp logging behavior to treat processes that are being inspected via the audit subsystem the same as processes that aren't under inspection. Handled actions will no longer be logged just because the process is being inspected. Since v4.14, applications have the ability to request logging of handled actions by using the SECCOMP_FILTER_FLAG_LOG flag when loading seccomp filters. With this patch, the logic for deciding if an action will be logged is: if action == RET_ALLOW: do not log else if action not in actions_logged: do not log else if action == RET_KILL: log else if action == RET_LOG: log else if filter-requests-logging: log else: do not log Reported-by: Steve Grubb <sgrubb(a)redhat.com&gt; Signed-off-by: Tyler Hicks <tyhicks(a)canonical.com&gt; --- Documentation/userspace-api/seccomp_filter.rst | 7 ------- include/linux/audit.h | 10 +--------- kernel/auditsc.c | 14 +++++++++++++- kernel/seccomp.c | 15 +++++---------- 4 files changed, 19 insertions(+), 27 deletions(-) diff --git a/Documentation/userspace-api/seccomp_filter.rst b/Documentation/userspace-api/seccomp_filter.rst index 099c412..82a468b 100644 --- a/Documentation/userspace-api/seccomp_filter.rst +++ b/Documentation/userspace-api/seccomp_filter.rst @@ -207,13 +207,6 @@ directory. Here's a description of each file in that directory: to the file do not need to be in ordered form but reads from the file will be ordered in the same way as the actions_avail sysctl. - It is important to note that the value of ``actions_logged`` does not - prevent certain actions from being logged when the audit subsystem is - configured to audit a task. If the action is not found in - ``actions_logged`` list, the final decision on whether to audit the - action for that task is ultimately left up to the audit subsystem to - decide for all seccomp return values other than ``SECCOMP_RET_ALLOW``. - The ``allow`` string is not accepted in the ``actions_logged`` sysctl as it is not possible to log ``SECCOMP_RET_ALLOW`` actions. Attempting to write ``allow`` to the sysctl will result in an EINVAL being diff --git a/include/linux/audit.h b/include/linux/audit.h index d4e35e7..b639cf1 100644 --- a/include/linux/audit.h +++ b/include/linux/audit.h @@ -232,7 +232,7 @@ extern void __audit_file(const struct file *); extern void __audit_inode_child(struct inode *parent, const struct dentry *dentry, const unsigned char type); -extern void __audit_seccomp(unsigned long syscall, long signr, int code); +extern void audit_seccomp(unsigned long syscall, long signr, int code); extern void audit_seccomp_actions_logged(const char *names, const char *old_names, int res); extern void __audit_ptrace(struct task_struct *t); @@ -304,12 +304,6 @@ static inline void audit_inode_child(struct inode *parent, } void audit_core_dumps(long signr); -static inline void audit_seccomp(unsigned long syscall, long signr, int code) -{ - if (audit_enabled && unlikely(!audit_dummy_context())) - __audit_seccomp(syscall, signr, code); -} - static inline void audit_ptrace(struct task_struct *t) { if (unlikely(!audit_dummy_context())) @@ -500,8 +494,6 @@ static inline void audit_inode_child(struct inode *parent, { } static inline void audit_core_dumps(long signr) { } -static inline void __audit_seccomp(unsigned long syscall, long signr, int code) -{ } static inline void audit_seccomp(unsigned long syscall, long signr, int code) { } static inline void audit_seccomp_actions_logged(const char *names, diff --git a/kernel/auditsc.c b/kernel/auditsc.c index 5a0b770..1512832 100644 --- a/kernel/auditsc.c +++ b/kernel/auditsc.c @@ -2464,7 +2464,19 @@ void audit_core_dumps(long signr) audit_log_end(ab); } -void __audit_seccomp(unsigned long syscall, long signr, int code) +/** + * audit_seccomp - record information about a seccomp action + * @syscall: syscall number + * @signr: signal value + * @code: the seccomp action + * + * Record the information associated with a seccomp action. Event filtering for + * seccomp actions that are not to be logged is done in seccomp_log(). + * Therefore, this function forces auditing independent of the audit_enabled + * and dummy context state because seccomp actions should be logged even when + * audit is not in use. + */ +void audit_seccomp(unsigned long syscall, long signr, int code) { struct audit_buffer *ab; diff --git a/kernel/seccomp.c b/kernel/seccomp.c index da78835..9029d9d 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -584,18 +584,13 @@ static inline void seccomp_log(unsigned long syscall, long signr, u32 action, } /* - * Force an audit message to be emitted when the action is RET_KILL_*, - * RET_LOG, or the FILTER_FLAG_LOG bit was set and the action is - * allowed to be logged by the admin. + * Emit an audit message when the action is RET_KILL_*, RET_LOG, or the + * FILTER_FLAG_LOG bit was set. The admin has the ability to silence + * any action from being logged by removing the action name from the + * seccomp_actions_logged sysctl. */ if (log) - return __audit_seccomp(syscall, signr, action); - - /* - * Let the audit subsystem decide if the action should be audited based - * on whether the current task itself is being audited. - */ - return audit_seccomp(syscall, signr, action); + audit_seccomp(syscall, signr, action); } /* -- 2.7.4

On Wed, May 2, 2018 at 12:57 PM, Kees Cook <keescook(a)chromium.org&gt; wrote: I got stuck doing some day job things today and didn't get a chance to look at v2 today, but I'll do that tomorrow. I'm not sure if you've already got anything queued up in your seccomp tree Kees, but if not I'm happy to take these patches via the audit tree; that was my original plan, assuming I got a positive nod from you. Either way, as long as it hits Linus' tree eventually I'll be happy (assuming everything looks good post-review of course). -- paul moore www.paul-moore.com