[IPV6]: Fix race in ipv6_flowlabel_opt() when inserting two labels
In the IPV6_FL_A_GET case the hash is checked for flowlabels with the given label. If it is not found, the lock, protecting the hash, is dropped to be re-get for writing. After this a newly allocated entry is inserted, but no checks are performed to catch a classical SMP race, when the conflicting label may be inserted on another cpu. Use the (currently unused) return value from fl_intern() to return the conflicting entry (if found) and re-check, whether we can reuse it (IPV6_FL_F_EXCL) or return -EEXISTS. Also add the comment, about why not re-lookup the current sock for conflicting flowlabel entry. Signed-off-by: Pavel Emelyanov <xemul@openvz.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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