tracing/probes: Fix to record 0-length data_loc in fetch_store_string*() if fails

Fix to record 0-length data to data_loc in fetch_store_string*() if it fails
to get the string data.
Currently those expect that the data_loc is updated by store_trace_args() if
it returns the error code. However, that does not work correctly if the
argument is an array of strings. In that case, store_trace_args() only clears
the first entry of the array (which may have no error) and leaves other
entries. So it should be cleared by fetch_store_string*() itself.
Also, 'dyndata' and 'maxlen' in store_trace_args() should be updated
only if it is used (ret > 0 and argument is a dynamic data.)

Link: https://lore.kernel.org/all/168908496683.123124.4761206188794205601.stgit@devnote2/

Fixes: 40b53b771806 ("tracing: probeevent: Add array type support")
Cc: stable@vger.kernel.org
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 8b92e34ff0c8..7b47e9a2c010 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -170,7 +170,8 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 			 */
 			ret++;
 		*(u32 *)dest = make_data_loc(ret, (void *)dst - base);
-	}
+	} else
+		*(u32 *)dest = make_data_loc(0, (void *)dst - base);
 
 	return ret;
 }