FAILED: patch "[PATCH] mptcp: avoid combining some incoming suboptions" failed to apply to 5.10-stable tree
Subsystems (3)
[email protected]
maintainerThe patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x b6ee361524641f57b2e2363f7737f20e17f67827
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026082005-zodiac-chef-dadc@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From b6ee361524641f57b2e2363f7737f20e17f67827 Mon Sep 17 00:00:00 2001
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Mon, 3 Aug 2026 18:16:34 +0200
Subject: [PATCH] mptcp: avoid combining some incoming suboptions
Some MPTCP suboptions are mutually exclusive according to the RFC8684, but also because in different places, the code doesn't expect some combinations to be present. That's specially true for suboptions that would be present twice, but with different attributes.
The new restrictions are the same as the ones applied on the output side, with mptcp_write_options. The same rules can be reused with a small fix: an MP_FASTCLOSE can be used with a DSS when the sender picks this option [1], which is not the case on Linux. Here are the rules:
Which options can be used together?
X: mutually exclusive
O: often used together
C: can be used together in some cases
P: could be used together but we prefer not to (optimisations)
| Opt: | MPC | MPJ | DSS | ADD | RM | PRIO | FAIL | FC | |------|------|------|------|------|------|------|------|------| | MPC |------|------|------|------|------|------|------|------| | MPJ | X |------|------|------|------|------|------|------| | DSS | X | X |------|------|------|------|------|------| | ADD | X | X | P |------|------|------|------|------| | RM | C | C | C | P |------|------|------|------| | PRIO | X | C | C | C | C |------|------|------| | FAIL | X | X | C | X | X | X |------|------| | FC | X | X | P | X | X | X | X |------| | RST | X | X | X | X | X | X | O | O | |------|------|------|------|------|------|------|------|------|
The only difference is with the 'P': another stack could send and ADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be allowed.
A few points of attention:
- In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is no reason to add it with a SYN. Note that even with a 4th ACK, it doesn't seem to be useful, except when IDs are known in advance via another channel. Better not to break that.
- Now, combining both an MP_CAPABLE and an MP_JOIN will no longer result to a reject of the two options, but only the second suboption is ignored. That seems OK to do that for this unexpected error. At least now all inconsistent combinations are handled the same way. This could change later in next. This also means the explicit checks for having both MPC + MPJ in subflow.c will now be unreachable. That's fine, they will be removed in a follow-up patch.
- In case of conflicting combinations, the extra suboption(s) is/are
ignored: having such combinations either means the remote peer is buggy, or is evil. The simplest action is then taken in this case:
stop processing the current suboption.
- In mp_opt->suboptions, there is also a bit reserved to the checksum, which can be used in an MP_CAPABLE and a DSS. Each time a DSS option can be used in parallel with another option, the checksum can be set, so the verification is combined into a new OPTIONS_MPTCP_DSS macro.
- An MP_CAPABLE ACK can carry a Data-Level Length, and an optional
Checksum: they are the same as the ones found in a DSS, because a DSS cannot be used in parallel to an MP_CAPABLE. Similarly, even if there is room, a DSS cannot be used with an MP_JOIN.
net/mptcp/options.c +58 -1
@@ -50,6 +50,14 @@ static void mptcp_parse_option(const struct sk_buff *skb, } } +/* Only the MPC + ACK can be used with a RM_ADDR */ +if (subopt ==OPTION_MPTCP_MPC_ACK ) { +if ((mp_opt->suboptions & ~OPTION_MPTCP_RM_ADDR ) !=0 ) +break ; + }else if (mp_opt->suboptions !=0 ) { +break ; + } +/* Cfr RFC 8684 Section 3.3.0: * If a checksum is present but its use had * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
@@ -122,6 +130,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_MP_JOIN : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTION_MPTCP_RM_ADDR | +OPTION_MPTCP_PRIO )) !=0 ) +break ; +if (opsize ==TCPOLEN_MPTCP_MPJ_SYN ) { mp_opt->suboptions |=OPTION_MPTCP_MPJ_SYN ; mp_opt->backup = *ptr++ &MPTCPOPT_BACKUP ;
@@ -153,6 +166,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_DSS : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTION_MPTCP_ADD_ADDR | +OPTION_MPTCP_RM_ADDR | +OPTION_MPTCP_PRIO | +OPTION_MPTCP_FASTCLOSE | +OPTION_MPTCP_FAIL )) !=0 ) +break ; +pr_debug ("DSS\n" ); ptr++;
@@ -240,6 +261,12 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_ADD_ADDR : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS | +OPTION_MPTCP_RM_ADDR | +OPTION_MPTCP_PRIO )) !=0 ) +break ; + mp_opt->echo = (*ptr++) &MPTCP_ADDR_ECHO ;if (!mp_opt->echo) { if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
@@ -299,6 +326,14 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_RM_ADDR : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTION_MPTCP_MPC_ACK | +OPTIONS_MPTCP_MPJ | +OPTIONS_MPTCP_DSS | +OPTION_MPTCP_ADD_ADDR | +OPTION_MPTCP_PRIO )) !=0 ) +break ; +if (opsize <TCPOLEN_MPTCP_RM_ADDR_BASE +1 || opsize >TCPOLEN_MPTCP_RM_ADDR_BASE +MPTCP_RM_IDS_MAX )break ;
@@ -313,6 +348,13 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_MP_PRIO : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_MPJ | +OPTIONS_MPTCP_DSS | +OPTION_MPTCP_ADD_ADDR | +OPTION_MPTCP_RM_ADDR )) !=0 ) +break ; +if (opsize !=TCPOLEN_MPTCP_PRIO )break ;
@@ -322,6 +364,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_MP_FASTCLOSE : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS | +OPTION_MPTCP_RST )) !=0 ) +break ; +if (opsize !=TCPOLEN_MPTCP_FASTCLOSE )break ;
@@ -333,6 +380,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_RST : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTION_MPTCP_FAIL | +OPTION_MPTCP_FASTCLOSE )) !=0 ) +break ; +if (opsize !=TCPOLEN_MPTCP_RST )break ;
@@ -348,6 +400,11 @@ static void mptcp_parse_option(const struct sk_buff *skb,break ;case MPTCPOPT_MP_FAIL : +/* Can be used with a restricted number of other options */ +if ((mp_opt->suboptions & ~(OPTIONS_MPTCP_DSS | +OPTION_MPTCP_RST )) !=0 ) +break ; +if (opsize !=TCPOLEN_MPTCP_FAIL )break ;
@@ -1406,7 +1463,7 @@ void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp,* RM | C | C | C | P |------|------|------|------| * PRIO | X | C | C | C | C |------|------|------| * FAIL | X | X | C | X | X | X |------|------| -* FC | X | X | X | X | X | X | X |------| +* FC | X | X | P | X | X | X | X |------| * RST | X | X | X | X | X | X | O | O | * ------|------|------|------|------|------|------|------|------| *
net/mptcp/protocol.h +1 -0
@@ -37,6 +37,7 @@ OPTION_MPTCP_MPC_ACK)#define OPTIONS_MPTCP_MPJ (OPTION_MPTCP_MPJ_SYN | OPTION_MPTCP_MPJ_SYNACK | \ OPTION_MPTCP_MPJ_ACK) +#define OPTIONS_MPTCP_DSS (OPTION_MPTCP_DSS | OPTION_MPTCP_CSUMREQD)/* MPTCP option subtypes */ #define MPTCPOPT_MP_CAPABLE 0