memcpy() call with "idata == NULL && ilen == 0" results in undefined
behavior in ar5523_cmd(). For example, NULL is passed in callchain
"ar5523_stat_work() -> ar5523_cmd_write() -> ar5523_cmd()". This patch
adds idata check before memcpy() call in ar5523_cmd() to prevent an
undefined behavior.

Cc: Pontus Fuchs <redacted>
Cc: Kalle Valo <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: stable@vger.kernel.org
Signed-off-by: Denis Efremov <efremov@linux.com>
---
 drivers/net/wireless/ath/ar5523/ar5523.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ar5523/ar5523.c b/drivers/net/wireless/ath/ar5523/ar5523.c
index b94759daeacc..f25af5bc5282 100644
--- a/drivers/net/wireless/ath/ar5523/ar5523.c
+++ b/drivers/net/wireless/ath/ar5523/ar5523.c

@@ -255,7 +255,8 @@ static int ar5523_cmd(struct ar5523 *ar, u32 code, const void *idata,
 
 	if (flags & AR5523_CMD_FLAG_MAGIC)
 		hdr->magic = cpu_to_be32(1 << 24);
-	memcpy(hdr + 1, idata, ilen);
+	if (idata)
+		memcpy(hdr + 1, idata, ilen);
 
 	cmd->odata = odata;
 	cmd->olen = olen;

-- 
2.21.0