libceph: fix undefined behavior when using snprintf()

The variable "str" is used as both the source and destination in
function snprintf(), which is undefined behavior based on C11. The
original description in C11 is:
	"If copying takes place between objects that
	overlap, the behavior is undefined."

And, the function of ceph_osdmap_state_str() is to return the osdmap
state, so it should return "doesn't exist" when all the conditions
are not satisfied. I fix it in this patch.

[elder@inktank.com: shortened the commit message]

Signed-off-by: Cong Ding <dinggnu@gmail.com>
Reviewed-by: Alex Elder <elder@inktank.com>

diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
index 369f03ba9ee53b5bba477eebb3d0f9932b9544b8..3c61e21611d3c5a5e666c9bf6c46126ea95f927b 100644 (file)
--- a/net/ceph/osdmap.c
+++ b/net/ceph/osdmap.c
@@ -13,26 +13,18 @@
 
 char *ceph_osdmap_state_str(char *str, int len, int state)
 {
-       int flag = 0;
-
        if (!len)
-               goto done;
-
-       *str = '\0';
-       if (state) {
-               if (state & CEPH_OSD_EXISTS) {
-                       snprintf(str, len, "exists");
-                       flag = 1;
-               }
-               if (state & CEPH_OSD_UP) {
-                       snprintf(str, len, "%s%s%s", str, (flag ? ", " : ""),
-                                "up");
-                       flag = 1;
-               }
-       } else {
+               return str;
+
+       if ((state & CEPH_OSD_EXISTS) && (state & CEPH_OSD_UP))
+               snprintf(str, len, "exists, up");
+       else if (state & CEPH_OSD_EXISTS)
+               snprintf(str, len, "exists");
+       else if (state & CEPH_OSD_UP)
+               snprintf(str, len, "up");
+       else
                snprintf(str, len, "doesn't exist");
-       }
-done:
+
        return str;
 }