[PATCH v2] pstore/ram: no timekeeping calls when unavailable

[Kees Cook]

We must not call timekeeping functions unless they are available. If we dump
before they have resumed, avoid a WARN_ON by setting the timestamp to 0.

Since the "ram" pstore driver can be a module, we must have
timekeeping_suspended exported.

Reported-by: Doug Anderson <diand...@chromium.org>
Cc: Anton Vorontsov <cbouatmai...@gmail.com>
Cc: John Stultz <johns...@us.ibm.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
v2:
 - export needed for timekeeping_suspended (thanks to Fengguang Wu).
---
 fs/pstore/ram.c           |    8 +++++++-
 kernel/time/timekeeping.c |    1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 1a4f6da..6d014e0 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -171,7 +171,13 @@ static size_t ramoops_write_kmsg_hdr(struct 
persistent_ram_zone *prz)
        struct timeval timestamp;
        size_t len;
 
-       do_gettimeofday(&timestamp);
+       /* Handle dumping before timekeeping has resumed. */
+       if (unlikely(timekeeping_suspended)) {
+               timestamp.tv_sec = 0;
+               timestamp.tv_usec = 0;
+       } else
+               do_gettimeofday(&timestamp);
+
        hdr = kasprintf(GFP_ATOMIC, RAMOOPS_KERNMSG_HDR "%lu.%lu\n",
                (long)timestamp.tv_sec, (long)timestamp.tv_usec);
        WARN_ON_ONCE(!hdr);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e424970..24ea968 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -33,6 +33,7 @@ __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
 
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
+EXPORT_SYMBOL_GPL(timekeeping_suspended);
 
 static inline void tk_normalize_xtime(struct timekeeper *tk)
 {
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
--
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