[PATCH v2] ar5523: check NULL before memcpy() in ar5523_cmd()

[Denis Efremov]

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 ilen check before memcpy() call in ar5523_cmd() to prevent an
undefined behavior.

Cc: Pontus Fuchs <pontus.fu...@gmail.com>
Cc: Kalle Valo <kv...@codeaurora.org>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: David Laight <david.lai...@aculab.com>
Cc: sta...@vger.kernel.org
Signed-off-by: Denis Efremov <efre...@linux.com>
---
V2: check ilen instead of idata as suggested by David Laight.

 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..da2d179430ca 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 (ilen)
+               memcpy(hdr + 1, idata, ilen);
 
        cmd->odata = odata;
        cmd->olen = olen;
-- 
2.21.0