[Crash-utility] [PATCH v4] Fix "log" command when crash is started with "--minimal" option

[Dave Wysochanski]

Commit c86250bce29f introduced the useful '-T' option to print the
log timestamp in human-readable form.  However, this option does
not work when crash is invoked with '--minimal' mode, and if tried,
crash will spin at 100% and continuously crash at a divide by 0
because machdep->hz == 0.

Fix this by disallowing this option in minimal mode.  In addition,
only calculate the logic to calculate kt->boot_date.tv_sec
when this option is enabled.

Fixes: c86250bce29f ("Introduction of the "log -T" option...")
Signed-off-by: Dave Wysochanski <dwysocha at redhat.com>
Reviewed-by: Wang Long <w at laoqinren.net>
Tested-by: Mathias Krause <minipli at grsecurity.net>
Reviewed-by: Lianbo Jiang <lijiang at redhat.com>
---
 kernel.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/kernel.c b/kernel.c
index 5ed6021..9aa1d4d 100644
--- a/kernel.c
+++ b/kernel.c
@@ -4939,13 +4939,20 @@ cmd_log(void)
         if (argerrs)
                 cmd_usage(pc->curcmd, SYNOPSIS);
 
-	if (kt->boot_date.tv_sec == 0) {
-		ulonglong uptime_jiffies;
-		ulong  uptime_sec;
-		get_uptime(NULL, &uptime_jiffies);
-		uptime_sec = (uptime_jiffies)/(ulonglong)machdep->hz;
-		kt->boot_date.tv_sec = kt->date.tv_sec - uptime_sec;
-		kt->boot_date.tv_nsec = 0;
+	if (msg_flags & SHOW_LOG_CTIME) {
+		if (pc->flags & MINIMAL_MODE) {
+			error(WARNING, "log: option 'T' not available in minimal mode\n");
+			return;
+		}
+
+		if (kt->boot_date.tv_sec == 0) {
+			ulonglong uptime_jiffies;
+			ulong  uptime_sec;
+			get_uptime(NULL, &uptime_jiffies);
+			uptime_sec = (uptime_jiffies)/(ulonglong)machdep->hz;
+			kt->boot_date.tv_sec = kt->date.tv_sec - uptime_sec;
+			kt->boot_date.tv_nsec = 0;
+		}
 	}
 
 	if (msg_flags & SHOW_LOG_AUDIT) {
-- 
2.27.0