[PATCH] tracing: fix potential null pointer dereference on rctr_end

[Colin King]

From: Colin Ian King <colin.k...@canonical.com>

Currently rctr_end may assigned null if strchr() fails leading to
a null pointer dereference in the following check on *(rctr_end + 1).
Fix this by also adding a null pointer check before the dereference.

Detected by CoverityScan, CID#1473700 ("Dereference null return value")

Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count 
(semaphore)")
Signed-off-by: Colin Ian King <colin.k...@canonical.com>
---
 kernel/trace/trace_uprobe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 3a7c73c40007..c5514651e61f 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -477,7 +477,7 @@ static int create_trace_uprobe(int argc, char **argv)
        rctr = strchr(arg, '(');
        if (rctr) {
                rctr_end = strchr(rctr, ')');
-               if (rctr > rctr_end || *(rctr_end + 1) != 0) {
+               if (!rctr_end || rctr > rctr_end || *(rctr_end + 1) != 0) {
                        ret = -EINVAL;
                        pr_info("Invalid reference counter offset.\n");
                        goto fail_address_parse;
-- 
2.17.1