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[dm-devel] [PATCH 4/21] [libmultipath] Fix overflow in circular queue

Multipathd has a circular buffer where messages are stored prior to being
passed into the system logs. Under certain circumstances the circular buffer
fills up; and the intention appears to be that new messages are dropped until
space is freed in the buffer.

However sometimes the result of a full circular buffer is to overwrite the
earlier messages before they have been passed to the system buffer; resulting
in the loss of early messages and corruption of later messages.

Signed-off-by: Hannes Reinecke <hare suse de>
 libmultipath/log.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/libmultipath/log.c b/libmultipath/log.c
index 8b339d7..90e4d1f 100644
--- a/libmultipath/log.c
+++ b/libmultipath/log.c
@@ -118,6 +118,11 @@ int log_enqueue (int prio, const char *
 	/* not enough space on tail : rewind */
 	if (la->head <= la->tail && len > (la->end - la->tail)) {
 		logdbg(stderr, "enqueue: rewind tail to %p\n", la->tail);
+                if (la->head == la->start ) {
+                        logdbg(stderr, "enqueue: can not rewind tail, drop msg\n");
+                        la->tail = lastmsg;
+                        return 1;  /* can't reuse */
+                }
 		la->tail = la->start;
 		if (la->empty)

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