From: Arthur Mongodin amongodin@randorisec.fr

Because of the size restriction in the TCP options space, the MPTCP ADD_ADDR option is exclusive and cannot be sent with other MPTCP ones. For this reason, in the linked mptcp_out_options structure, group of fields linked to different options are part of the same union.

There is a case where the mptcp_pm_add_addr_signal() function can modify opts->addr, but not ended up sending an ADD_ADDR. Later on, back in mptcp_established_options, other options will be sent, but with unexpected data written in other fields due to the union, e.g. in opts->ext_copy. This could lead to a data stream corruption in the next packet.

Using an intermediate variable, prevents from corrupting previously established DSS option. The assignment of the ADD_ADDR option parameters is now done once we are sure this ADD_ADDR option can be set in the packet, e.g. after having dropped other suboptions.

Fixes: 1bff1e43a30e ("mptcp: optimize out option generation") Cc: stable@vger.kernel.org Suggested-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Arthur Mongodin amongodin@randorisec.fr Reviewed-by: Matthieu Baerts (NGI0) matttbe@kernel.org [ Matt: the commit message has been updated: long lines splits and some clarifications. ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- net/mptcp/options.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c index fd2de185bc939f8730e87a63ac02a015e610e99c..23949ae2a3a8db19d05c5c8373f45c885c3523ad 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -651,6 +651,7 @@ static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff * struct mptcp_sock *msk = mptcp_sk(subflow->conn); bool drop_other_suboptions = false; unsigned int opt_size = *size; + struct mptcp_addr_info addr; bool echo; int len;

@@ -659,7 +660,7 @@ static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff * */ if (!mptcp_pm_should_add_signal(msk) || (opts->suboptions & (OPTION_MPTCP_MPJ_ACK | OPTION_MPTCP_MPC_ACK)) || - !mptcp_pm_add_addr_signal(msk, skb, opt_size, remaining, &opts->addr, + !mptcp_pm_add_addr_signal(msk, skb, opt_size, remaining, &addr, &echo, &drop_other_suboptions)) return false;

@@ -672,7 +673,7 @@ static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff * else if (opts->suboptions & OPTION_MPTCP_DSS) return false;

- len = mptcp_add_addr_len(opts->addr.family, echo, !!opts->addr.port); + len = mptcp_add_addr_len(addr.family, echo, !!addr.port); if (remaining < len) return false;

@@ -689,6 +690,7 @@ static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff * opts->ahmac = 0; *size -= opt_size; } + opts->addr = addr; opts->suboptions |= OPTION_MPTCP_ADD_ADDR; if (!echo) { MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDRTX);