Re: [PATCH] audit: check the length of userspace generated audit records

On 2020-04-20 17:36, Paul Moore wrote: > Commit 756125289285 ("audit: always check the netlink payload length > in audit_receive_msg()") fixed a number of missing message length > checks, but forgot to check the length of userspace generated audit > records. The good news is that you need CAP_AUDIT_WRITE to submit > userspace audit records, which is generally only given to trusted > processes, so the impact should be limited. > > Cc: stable(a)vger.kernel.org > Fixes: 756125289285 ("audit: always check the netlink payload length in audit_receive_msg()") > Reported-by: syzbot+49e69b4d71a420ceda3e(a)syzkaller.appspotmail.com > Signed-off-by: Paul Moore <paul(a)paul-moore.com&gt; > --- > kernel/audit.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/audit.c b/kernel/audit.c > index b69c8b460341..87f31bf1f0a0 100644 > --- a/kernel/audit.c > +++ b/kernel/audit.c > @@ -1326,6 +1326,9 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) > case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2: > if (!audit_enabled && msg_type != AUDIT_USER_AVC) > return 0; > + /* exit early if there isn't at least one character to print */ > + if (data_len < 2) > + return -EINVAL; Don't we want to issue the record even if the message is empty? If a len of 1 is passed in, it will properly set str[0] = '\0' and str points to a location with a null that prints nothing between the single quotes of "msg=''". So, I think that should be "if (data_len < 1)". Am I missing something?