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Subject[PATCH v2] pstore/ram: no timekeeping calls when unavailable
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 <dianders@chromium.org>
Cc: Anton Vorontsov <cbouatmailru@gmail.com>
Cc: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Kees Cook <keescook@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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