Re: [PATCH] TaskTracker : Simplified thread information tracker.

From: Tetsuo Handa
Date: Mon Jan 12 2015 - 01:13:30 EST

Thank you for comments.

Richard Guy Briggs wrote:
> Steve already mentioned any user-influenced fields need to be escaped,
> so I'd recommend audit_log_untrustedstring() as being much simpler from
> your perspective and much better tested and understood from audit
> maintainer's perspective. At least use the existing 'o' printf format
> specifier instead of inventing your own. I do acknowledge that the
> resulting output from your function is easier to read in its raw format
> passed from the kernel, however, it makes your code harder to maintain.

I'm not sure whether I should use audit_log_untrustedstring().

This record contains multiple user-influenced comm names. If I use
audit_log_untrustedstring(), I would need to split this record into
multiple records like history[0]='...' history[1]='...' history[2]='...'
in order to avoid matching delimiters (i.e. ';', '=' and '>') used in
this record. This would also change from "char *" in "struct task_struct"
to array of struct { "comm name", "pid", "stamp" } in "struct task_struct".
I don't know whether such change makes easier to maintain than now.

> As for the date-stamping bits, they seem to be the majority of the code
> in audit_update_history(). I'd just emit a number and punt that to
> userspace for decoding. Alternatively, I'd use an existing service in
> the kernel to do that date formatting, or at least call a new function
> to format that date string should a suitable one not already exist, so
> you can remove that complexity from audit_update_history().

Since I don't know existing functions for date formatting, I split it as
a new function. If it is acceptable, I'd like to make that function public
and replace tomoyo_convert_time() in security/tomoyo/util.c with that
function.

Regards.
----------------------------------------
>From 50d59b5640a7501b8d5f843fb57283fcb62b1118 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 12 Jan 2015 14:45:23 +0900
Subject: [PATCH] audit: Emit history of thread's comm name.

When an unexpected system event (e.g. reboot) occurs, the administrator may
want to identify which application triggered the event. System call auditing
could be used for recording such event. However, the audit log may not be
able to provide sufficient information for identifying the application
because the audit log does not reflect how the program was executed.

This patch adds ability to trace how the program was executed and emit it
as an auxiliary record in the form of comm name, pid and time stamp pairs
as of execve().

type=UNKNOWN[1329] msg=audit(1421039813.810:3693): history='
name=swapper\0570;pid=1;start=20150112140720=>name=init;pid=1;
start=20150112140721=>name=systemd;pid=1;start=20150112140722=>
name=sshd;pid=2473;start=20150112050733=>name=sshd;pid=9838;
start=20150112051105=>name=bash;pid=9840;start=20150112051108=>
name=tail;pid=9876;start=20150112051653'

Since converting all bytes using audit_log_untrustedstring() makes this record
unparsable because this record includes multiple user-influenced comm names
which may match delimiters used in this record (i.e. ';', '=' and '>'), only
bytes which are not alphabets, numbers, '.', '_' nor '-' are escaped.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 1 +
include/linux/audit.h | 4 ++
include/linux/init_task.h | 5 ++
include/linux/sched.h | 3 +
include/uapi/linux/audit.h | 1 +
kernel/audit.c | 1 +
kernel/auditsc.c | 155 +++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 170 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index ad8798e..5e92651 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1200,6 +1200,7 @@ void install_exec_creds(struct linux_binprm *bprm)
commit_creds(bprm->cred);
bprm->cred = NULL;

+ audit_update_history();
/*
* Disable monitoring for regular users
* when executing setuid binaries. Must
diff --git a/include/linux/audit.h b/include/linux/audit.h
index af84234..74310a7 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -221,6 +221,8 @@ static inline void audit_ptrace(struct task_struct *t)
__audit_ptrace(t);
}

+extern void audit_update_history(void);
+
/* Private API (for audit.c only) */
extern unsigned int audit_serial(void);
extern int auditsc_get_stamp(struct audit_context *ctx,
@@ -437,6 +439,8 @@ static inline void audit_mmap_fd(int fd, int flags)
{ }
static inline void audit_ptrace(struct task_struct *t)
{ }
+static inline void audit_update_history(void)
+{ }
#define audit_n_rules 0
#define audit_signals 0
#endif /* CONFIG_AUDITSYSCALL */
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 3037fc0..078823a 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -98,8 +98,12 @@ extern struct group_info init_groups;
#define INIT_IDS \
.loginuid = INVALID_UID, \
.sessionid = (unsigned int)-1,
+extern char init_task_history[];
+#define INIT_THREAD_HISTORY \
+ .comm_history = init_task_history,
#else
#define INIT_IDS
+#define INIT_THREAD_HISTORY
#endif

#ifdef CONFIG_PREEMPT_RCU
@@ -247,6 +251,7 @@ extern struct task_group root_task_group;
INIT_RT_MUTEXES(tsk) \
INIT_VTIME(tsk) \
INIT_NUMA_BALANCING(tsk) \
+ INIT_THREAD_HISTORY \
}


diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef..77539e4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1701,6 +1701,9 @@ struct task_struct {
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
+#ifdef CONFIG_AUDITSYSCALL
+ char *comm_history;
+#endif
};

/* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index d3475e1..93ad58c 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -110,6 +110,7 @@
#define AUDIT_SECCOMP 1326 /* Secure Computing event */
#define AUDIT_PROCTITLE 1327 /* Proctitle emit event */
#define AUDIT_FEATURE_CHANGE 1328 /* audit log listing feature changes */
+#define AUDIT_PROCHISTORY 1329 /* Commname history emit event */

#define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
#define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
diff --git a/kernel/audit.c b/kernel/audit.c
index 72ab759..d45397e 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1154,6 +1154,7 @@ static int __init audit_init(void)
{
int i;

+ audit_update_history();
if (audit_initialized == AUDIT_DISABLED)
return 0;

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 072566d..2edeba2 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -88,6 +88,9 @@
/* max length to print of cmdline/proctitle value during audit */
#define MAX_PROCTITLE_AUDIT_LEN 128

+/* thread's comm name history length */
+#define COMM_HISTORY_SIZE 1024
+
/* number of audit rules */
int audit_n_rules;

@@ -945,6 +948,11 @@ int audit_alloc(struct task_struct *tsk)
enum audit_state state;
char *key = NULL;

+ tsk->comm_history = kmemdup(current->comm_history, COMM_HISTORY_SIZE,
+ GFP_KERNEL);
+ if (!tsk->comm_history)
+ return -ENOMEM;
+
if (likely(!audit_ever_enabled))
return 0; /* Return if not auditing. */

@@ -955,6 +963,8 @@ int audit_alloc(struct task_struct *tsk)
}

if (!(context = audit_alloc_context(state))) {
+ kfree(tsk->comm_history);
+ tsk->comm_history = NULL;
kfree(key);
audit_log_lost("out of memory in audit_alloc");
return -ENOMEM;
@@ -1344,6 +1354,17 @@ out:
audit_log_end(ab);
}

+static void audit_log_history(struct audit_context *context)
+{
+ struct audit_buffer *ab;
+
+ ab = audit_log_start(context, GFP_KERNEL, AUDIT_PROCHISTORY);
+ if (!ab)
+ return; /* audit_panic or being filtered */
+ audit_log_format(ab, "history='%s'", current->comm_history);
+ audit_log_end(ab);
+}
+
static void audit_log_exit(struct audit_context *context, struct task_struct *tsk)
{
int i, call_panic = 0;
@@ -1462,6 +1483,7 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
}

audit_log_proctitle(tsk, context);
+ audit_log_history(context);

/* Send end of event record to help user space know we are finished */
ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
@@ -1481,6 +1503,8 @@ void __audit_free(struct task_struct *tsk)
{
struct audit_context *context;

+ kfree(tsk->comm_history);
+ tsk->comm_history = NULL;
context = audit_take_context(tsk, 0, 0);
if (!context)
return;
@@ -2535,3 +2559,134 @@ struct list_head *audit_killed_trees(void)
return NULL;
return &ctx->killed_trees;
}
+
+char init_task_history[COMM_HISTORY_SIZE];
+
+/* Structure for representing YYYY/MM/DD hh/mm/ss. */
+struct yyyymmdd_hhmmss {
+ u16 year;
+ u8 month;
+ u8 day;
+ u8 hour;
+ u8 min;
+ u8 sec;
+};
+
+/**
+ * tt_get_time - Get current time in YYYY/MM/DD hh/mm/ss format.
+ *
+ * @stamp: Pointer to "struct yyyymmdd_hhmmss".
+ *
+ * Returns nothing.
+ *
+ * This function does not handle Y2038 problem.
+ */
+static void tt_get_time(struct yyyymmdd_hhmmss *stamp)
+{
+ static const u16 days_until_end_of_month[2][12] = {
+ { 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
+ { 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
+ };
+ u16 y = 1970;
+ u8 m;
+ bool r;
+ time_t time = get_seconds();
+
+ stamp->sec = time % 60;
+ time /= 60;
+ stamp->min = time % 60;
+ time /= 60;
+ stamp->hour = time % 24;
+ time /= 24;
+ if (time >= 16436) {
+ /* Start from 2015/01/01 rather than 1970/01/01. */
+ time -= 16436;
+ y += 45;
+ }
+ while (1) {
+ const unsigned short days = (y & 3) ? 365 : 366;
+
+ if (time < days)
+ break;
+ time -= days;
+ y++;
+ }
+ r = (y & 3) == 0;
+ for (m = 0; m < 11 && time >= days_until_end_of_month[r][m]; m++)
+ ;
+ if (m)
+ time -= days_until_end_of_month[r][m - 1];
+ stamp->year = y;
+ stamp->month = ++m;
+ stamp->day = ++time;
+}
+
+/**
+ * audit_update_history - Update current->comm_history field.
+ *
+ * Returns nothing.
+ *
+ * Update is done locklessly because current thread's history is updated by
+ * only current thread upon boot up and successful execve() operation, and
+ * we don't read other thread's history.
+ */
+void audit_update_history(void)
+{
+ char *cp;
+ int i;
+ int required;
+ char buf[256];
+
+ /*
+ * Lockless read because this is current thread and being unexpectedly
+ * modified by other thread is not a fatal problem.
+ */
+ cp = buf;
+ cp += snprintf(buf, sizeof(buf) - 1, "name=");
+ for (i = 0; i < TASK_COMM_LEN; i++) {
+ const unsigned char c = current->comm[i];
+
+ if (!c)
+ break;
+ if (isalnum(c) || c == '.' || c == '_' || c == '-') {
+ *cp++ = c;
+ continue;
+ }
+ *cp++ = '\\';
+ *cp++ = (c >> 6) + '0';
+ *cp++ = ((c >> 3) & 7) + '0';
+ *cp++ = (c & 7) + '0';
+ }
+ /* Append PID. */
+ cp += snprintf(cp, buf - cp + sizeof(buf) - 1, ";pid=%u",
+ current->pid);
+ /* Append timestamp. */
+ {
+ struct yyyymmdd_hhmmss stamp;
+
+ tt_get_time(&stamp);
+ cp += snprintf(cp, buf - cp + sizeof(buf) - 1,
+ ";start=%04u%02u%02u%02u%02u%02u", stamp.year,
+ stamp.month, stamp.day, stamp.hour, stamp.min,
+ stamp.sec);
+ }
+ /* Terminate the buffer. */
+ if (cp >= buf + sizeof(buf))
+ cp = buf + sizeof(buf) - 1;
+ *cp = '\0';
+ required = cp - buf;
+ /* Make some room by truncating old history. */
+ cp = current->comm_history;
+ while (i = strlen(cp), i + required >= COMM_HISTORY_SIZE - 10) {
+ char *cp2 = memchr(cp + 2, '>', i - 2);
+
+ BUG_ON(!cp2);
+ cp2--;
+ memmove(cp, cp2, strlen(cp2) + 1);
+ }
+ /* Emit the buffer. */
+ if (!i)
+ sprintf(cp, "%s", buf);
+ else
+ sprintf(cp + i, "=>%s", buf);
+}
--
1.8.3.1
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