Re: [PATCH] ifplugd

[Maxim Kryžanovský]

> > > Is this safe?
> > > 
> > > if (strncmp(G.iface, RTA_DATA(attr), len) == 0)
> > > 
> > > What if RTA_DATA(attr) = "if", len = 2, and G.iface = "if0"?
> > > Or does kernel pass attr with NUL included?
> 
> > Yes, it is not safe. It needs to compare their lengths:
> > int iface_len = strlen(G.iface);
> > if (iface_len == len && strncmp(G.iface, RTA_DATA(attr), len) == 0)
> 
> Ok, now what if RTA_DATA(attr) = "if\0", len = 3, and G.iface = "if"?
> Your code will think that strings aren't equal. Maybe
> 
> if (iface_len <= len && strncmp(G.iface, RTA_DATA(attr), len) == 0)
> 
> -- 
> vda
> 
> 
> 

Hi Denis.

The kernel pass attr with NUL included, but I could not determine
whether does this always. If so, the NUL can be omitted from the total
length to avoid the need to compare strings with different lengths.

diff --git a/networking/ifplugd.c b/networking/ifplugd.c
index 41b04c4..dcb6d4d 100644
--- a/networking/ifplugd.c
+++ b/networking/ifplugd.c
@@ -525,10 +525,10 @@ static NOINLINE int check_existence_through_netlink(void)
 
                                while (RTA_OK(attr, attr_len)) {
                                        if (attr->rta_type == IFLA_IFNAME) {
-                                               int len = RTA_PAYLOAD(attr);
+                                               int len = RTA_PAYLOAD(attr) - 1;
                                                if (len > IFNAMSIZ)
                                                        len = IFNAMSIZ;
-                                               if (iface_len <= len
+                                               if (iface_len == len
                                                 && strncmp(G.iface, RTA_DATA(attr), len) == 0
                                                ) {
                                                        G.iface_exists = (mhdr->nlmsg_type == RTM_NEWLINK);


Also attached is a fix to 'ENABLE_FEATURE_PIDFILE is not set'.
--
max
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