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Fix ifa refcount leak in ifa_ifwithnet()

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In 4f6c66cc9c, ifa_ifwithnet() was changed to no longer
ifa_ref() the returned ifaddr, and instead the caller was required
to stay in the net_epoch for as long as they wanted the ifaddr
to remain valid.  However, this missed the case where an AF_LINK
lookup would call ifaddr_byindex(), which still does ifa_ref()
the ifaddr.  This would cause a refcount leak.

Fix this by inlining the relevant parts of ifaddr_byindex() here,
with the ifa_ref() call removed.  This also avoids an unnecessary
entry and exit from the net_epoch for this case.

I've audited all in-tree consumers of ifa_ifwithnet() that could
possibly perform an AF_LINK lookup and confirmed that none of them
will expect the ifaddr to have a reference that they need to
release.

MFC after: 2 months
Sponsored by: Dell Inc
Differential Revision:	https://reviews.freebsd.org/D28705
Reviewed by: melifaro
This commit is contained in:
Ryan Stone 2021-02-11 11:17:58 -05:00
parent 32a95656b5
commit 5adea417d4
1 changed files with 9 additions and 3 deletions
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12
sys/net/if.c
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@ -1953,6 +1953,7 @@ ifa_ifwithnet(const struct sockaddr *addr, int ignore_ptp, int fibnum)
struct ifaddr *ifa_maybe = NULL;
u_int af = addr->sa_family;
const char *addr_data = addr->sa_data, *cplim;
const struct sockaddr_dl *sdl;
NET_EPOCH_ASSERT();
/*
@ -1960,9 +1961,14 @@ ifa_ifwithnet(const struct sockaddr *addr, int ignore_ptp, int fibnum)
* so do that if we can.
*/
if (af == AF_LINK) {
const struct sockaddr_dl *sdl = (const struct sockaddr_dl *)addr;
if (sdl->sdl_index && sdl->sdl_index <= V_if_index)
return (ifaddr_byindex(sdl->sdl_index));
sdl = (const struct sockaddr_dl *)addr;
if (sdl->sdl_index && sdl->sdl_index <= V_if_index) {
ifp = ifnet_byindex(sdl->sdl_index);
if (ifp == NULL)
return (NULL);
return (ifp->if_addr);
}
}
/*