acct: stop using get_seconds()

In 'struct acct', 'struct acct_v3', and 'struct taskstats' we have
a 32-bit 'ac_btime' field containing an absolute time value, which
will overflow in year 2106.

There are two possible ways to deal with it:

a) let it overflow and have user space code deal with reconstructing
   the data based on the current time, or
b) truncate the times based on the range of the u32 type.

Neither of them solves the actual problem. Pick the second
one to best document what the issue is, and have someone
fix it in a future version.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/include/uapi/linux/acct.h b/include/uapi/linux/acct.h
index 0e72172..985b890 100644 (file)
--- a/include/uapi/linux/acct.h
+++ b/include/uapi/linux/acct.h
@@ -49,6 +49,7 @@ struct acct
        __u16           ac_uid16;               /* LSB of Real User ID */
        __u16           ac_gid16;               /* LSB of Real Group ID */
        __u16           ac_tty;                 /* Control Terminal */
+       /* __u32 range means times from 1970 to 2106 */
        __u32           ac_btime;               /* Process Creation Time */
        comp_t          ac_utime;               /* User Time */
        comp_t          ac_stime;               /* System Time */
@@ -81,6 +82,7 @@ struct acct_v3
        __u32           ac_gid;                 /* Real Group ID */
        __u32           ac_pid;                 /* Process ID */
        __u32           ac_ppid;                /* Parent Process ID */
+       /* __u32 range means times from 1970 to 2106 */
        __u32           ac_btime;               /* Process Creation Time */
 #ifdef __KERNEL__
        __u32           ac_etime;               /* Elapsed Time */

diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
index 5e8ca16..7d3ea36 100644 (file)
--- a/include/uapi/linux/taskstats.h
+++ b/include/uapi/linux/taskstats.h
@@ -112,6 +112,7 @@ struct taskstats {
        __u32   ac_gid;                 /* Group ID */
        __u32   ac_pid;                 /* Process ID */
        __u32   ac_ppid;                /* Parent process ID */
+       /* __u32 range means times from 1970 to 2106 */
        __u32   ac_btime;               /* Begin time [sec since 1970] */
        __u64   ac_etime __attribute__((aligned(8)));
                                        /* Elapsed time [usec] */

diff --git a/kernel/acct.c b/kernel/acct.c
index 81f9831..11ff4a5 100644 (file)
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -416,6 +416,7 @@ static void fill_ac(acct_t *ac)
 {
        struct pacct_struct *pacct = &current->signal->pacct;
        u64 elapsed, run_time;
+       time64_t btime;
        struct tty_struct *tty;
 
        /*
@@ -448,7 +449,8 @@ static void fill_ac(acct_t *ac)
        }
 #endif
        do_div(elapsed, AHZ);
-       ac->ac_btime = get_seconds() - elapsed;
+       btime = ktime_get_real_seconds() - elapsed;
+       ac->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
 #if ACCT_VERSION==2
        ac->ac_ahz = AHZ;
 #endif

diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 7be3e75..ab12616 100644 (file)
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -24,6 +24,7 @@ void bacct_add_tsk(struct user_namespace *user_ns,
        const struct cred *tcred;
        u64 utime, stime, utimescaled, stimescaled;
        u64 delta;
+       time64_t btime;
 
        BUILD_BUG_ON(TS_COMM_LEN < TASK_COMM_LEN);
 
@@ -32,9 +33,10 @@ void bacct_add_tsk(struct user_namespace *user_ns,
        /* Convert to micro seconds */
        do_div(delta, NSEC_PER_USEC);
        stats->ac_etime = delta;
-       /* Convert to seconds for btime */
-       do_div(delta, USEC_PER_SEC);
-       stats->ac_btime = get_seconds() - delta;
+       /* Convert to seconds for btime (note y2106 limit) */
+       btime = ktime_get_real_seconds() - div_u64(delta, USEC_PER_SEC);
+       stats->ac_btime = clamp_t(time64_t, btime, 0, U32_MAX);
+
        if (thread_group_leader(tsk)) {
                stats->ac_exitcode = tsk->exit_code;
                if (tsk->flags & PF_FORKNOEXEC)