nl: avoid NULL pointer dereference

It's a valid case to call nla_put() with NULL data and 0 len. It's done e.g. in
the nla_put_attr().

There has to be a check for data in nla_put() as passing NULL to the memcpy()
is not allowed. Even if length is 0, both pointers have to be valid.

For a reference see C99 standard (7.21.1/2), it says: "pointer arguments on
such a call shall still have valid values".

Reported-by: Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
[christian.brauner@ubuntu.com: adapted commit message]
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/nl.c b/src/lxc/nl.c
index e1dd844329668af9d6fed98556cf45980ae79fe5..dfe71110fa3421799389427302d10c989b836456 100644 (file)
--- a/src/lxc/nl.c
+++ b/src/lxc/nl.c
@@ -61,7 +61,8 @@ static int nla_put(struct nlmsg *nlmsg, int attr,
        rta = NLMSG_TAIL(nlmsg->nlmsghdr);
        rta->rta_type = attr;
        rta->rta_len = rtalen;
-       memcpy(RTA_DATA(rta), data, len);
+       if (data && len)
+               memcpy(RTA_DATA(rta), data, len);
        nlmsg->nlmsghdr->nlmsg_len = tlen;
        return 0;
 }