time: jiffies_delta_to_clock_t() helper to the rescue

Various /proc/net files sometimes report crazy timer values, expressed
in clock_t units.

This happens when an expired timer delta (expires - jiffies) is passed
to jiffies_to_clock_t().

This function has an overflow in :

return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);

commit cbbc719fccdb8cb (time: Change jiffies_to_clock_t() argument type
to unsigned long) only got around the problem.

As we cant output negative values in /proc/net/tcp without breaking
various tools, I suggest adding a jiffies_delta_to_clock_t() wrapper
that caps the negative delta to a 0 value.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Maciej Żenczykowski <maze@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: hank <pyu@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 6699f23e6f55..0b5580c69f2d 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -2435,6 +2435,8 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
                 struct ip_mc_list *im = (struct ip_mc_list *)v;
                 struct igmp_mc_iter_state *state = igmp_mc_seq_private(seq);
                 char   *querier;
+                long delta;
+
 #ifdef CONFIG_IP_MULTICAST
                 querier = IGMP_V1_SEEN(state->in_dev) ? "V1" :
                           IGMP_V2_SEEN(state->in_dev) ? "V2" :
@@ -2448,11 +2450,12 @@ static int igmp_mc_seq_show(struct seq_file *seq, void *v)
                                    state->dev->ifindex, state->dev->name, state->in_dev->mc_count, querier);
                 }
 
+                delta = im->timer.expires - jiffies;
                 seq_printf(seq,
                            "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
                            im->multiaddr, im->users,
-                           im->tm_running, im->tm_running ?
-                           jiffies_to_clock_t(im->timer.expires-jiffies) : 0,
+                           im->tm_running,
+                           im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
                            im->reporter);
         }
         return 0;