core: dereference check on the variables in glusterfs_handle_brick_status

problem: In a race condition, the active->first which is supposed to be filled
is NULL and trying to dereference it crashs.

back trace:
Core was generated by `/usr/sbin/glusterfsd -s bxts470192.eu.rabonet.com --volfile-id prod_xvavol.bxts'.
Program terminated with signal 11, Segmentation fault.
1029            any = active->first;
(gdb) bt

Change-Id: Ia6291865319a9456b8b01a5251be2679c4985b7c
fixes: bz#1600451
Signed-off-by: Hari Gowtham <hgowtham@redhat.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/glusterfsd/src/glusterfsd-mgmt.c b/glusterfsd/src/glusterfsd-mgmt.c
index 7122fc0d127..f1b2f9e7123 100644
--- a/glusterfsd/src/glusterfsd-mgmt.c
+++ b/glusterfsd/src/glusterfsd-mgmt.c
@@ -1127,8 +1127,23 @@ glusterfs_handle_brick_status (rpcsvc_request_t *req)
         }
 
         ctx = glusterfsd_ctx;
-        GF_ASSERT (ctx);
+        if (ctx == NULL) {
+                gf_log (this->name, GF_LOG_ERROR, "ctx returned NULL");
+                ret = -1;
+                goto out;
+        }
+        if (ctx->active == NULL) {
+                gf_log (this->name, GF_LOG_ERROR, "ctx->active returned NULL");
+                ret = -1;
+                goto out;
+        }
         active = ctx->active;
+        if (ctx->active->first == NULL) {
+                gf_log (this->name, GF_LOG_ERROR, "ctx->active->first "
+                        "returned NULL");
+                ret = -1;
+                goto out;
+        }
         server_xl = active->first;
 
         brick_xl = get_xlator_by_name (server_xl, brickname);