net: fix double-free of nl_cache in initParent error paths

[sharadboni]

Summary

initParent in net.cc registers a defer { nl_cache_free(link_cache); } RAII guard that ensures link_cache is freed on all exit paths. However, the error returns inside the iface_own loop and the cloneIface block also called nl_cache_free(link_cache) explicitly, resulting in a double-free when moveToNs or cloneIface fails.

Reproduction

With a configuration that includes iface_own set to a nonexistent interface, nsjail calls moveToNs, which fails because rtnl_link_get_by_name returns NULL for the unknown interface. The explicit nl_cache_free fires, then the defer guard fires again on return false — double-free.

Under ASan:

AddressSanitizer:DEADLYSIGNAL
ERROR: AddressSanitizer: SEGV on unknown address
    in nl_cache_clear (libnl-3.so.200)
    in nl_cache_free (libnl-3.so.200)

Fix

Remove the two redundant explicit nl_cache_free(link_cache) calls from the error paths. The defer guard is sufficient to free link_cache on all code paths.

[mtasaka]

I don't know why me was mentioned...

[sharadboni]

@robertswiecki can you please take a look

[robertswiecki]

Thank you!