6.16-stable review patch. If anyone has any objections, please let me know.
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From: Jakub Kicinski kuba@kernel.org
[ Upstream commit 31557b3487b349464daf42bc4366153743c1e727 ]
A decade ago commit 6d08acd2d32e ("in6: fix conflict with glibc") hid the definitions of IPV6 options, because GCC was complaining about duplicates. The commit did not list the warnings seen, but trying to recreate them now I think they are (building iproute2):
In file included from ./include/uapi/rdma/rdma_user_cm.h:39, from rdma.h:16, from res.h:9, from res-ctx.c:7: ../include/uapi/linux/in6.h:171:9: warning: ‘IPV6_ADD_MEMBERSHIP’ redefined 171 | #define IPV6_ADD_MEMBERSHIP 20 | ^~~~~~~~~~~~~~~~~~~ In file included from /usr/include/netinet/in.h:37, from rdma.h:13: /usr/include/bits/in.h:233:10: note: this is the location of the previous definition 233 | # define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP | ^~~~~~~~~~~~~~~~~~~ ../include/uapi/linux/in6.h:172:9: warning: ‘IPV6_DROP_MEMBERSHIP’ redefined 172 | #define IPV6_DROP_MEMBERSHIP 21 | ^~~~~~~~~~~~~~~~~~~~ /usr/include/bits/in.h:234:10: note: this is the location of the previous definition 234 | # define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP | ^~~~~~~~~~~~~~~~~~~~
Compilers don't complain about redefinition if the defines are identical, but here we have the kernel using the literal value, and glibc using an indirection (defining to a name of another define, with the same numerical value).
Problem is, the commit in question hid all the IPV6 socket options, and glibc has a pretty sparse list. For instance it lacks Flow Label related options. Willem called this out in commit 3fb321fde22d ("selftests/net: ipv6 flowlabel"):
/* uapi/glibc weirdness may leave this undefined */ #ifndef IPV6_FLOWINFO #define IPV6_FLOWINFO 11 #endif
More interestingly some applications (socat) use a #ifdef IPV6_FLOWINFO to gate compilation of thier rudimentary flow label support. (For added confusion socat misspells it as IPV4_FLOWINFO in some places.)
Hide only the two defines we know glibc has a problem with. If we discover more warnings we can hide more but we should avoid covering the entire block of defines for "IPV6 socket options".
Link: https://patch.msgid.link/20250609143933.1654417-1-kuba@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/uapi/linux/in6.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/in6.h b/include/uapi/linux/in6.h index ff8d21f9e95b..5a47339ef7d7 100644 --- a/include/uapi/linux/in6.h +++ b/include/uapi/linux/in6.h @@ -152,7 +152,6 @@ struct in6_flowlabel_req { /* * IPV6 socket options */ -#if __UAPI_DEF_IPV6_OPTIONS #define IPV6_ADDRFORM 1 #define IPV6_2292PKTINFO 2 #define IPV6_2292HOPOPTS 3 @@ -169,8 +168,10 @@ struct in6_flowlabel_req { #define IPV6_MULTICAST_IF 17 #define IPV6_MULTICAST_HOPS 18 #define IPV6_MULTICAST_LOOP 19 +#if __UAPI_DEF_IPV6_OPTIONS #define IPV6_ADD_MEMBERSHIP 20 #define IPV6_DROP_MEMBERSHIP 21 +#endif #define IPV6_ROUTER_ALERT 22 #define IPV6_MTU_DISCOVER 23 #define IPV6_MTU 24 @@ -203,7 +204,6 @@ struct in6_flowlabel_req { #define IPV6_IPSEC_POLICY 34 #define IPV6_XFRM_POLICY 35 #define IPV6_HDRINCL 36 -#endif
/* * Multicast: