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9958e69b98
For IPv4 ERSPAN: In erspan_xmit(), the driver clears IP_TUNNEL_SEQ_BIT (for version 0) and IP_TUNNEL_KEY_BIT directly in the shared tunnel->parms.o_flags structure. Since transmit paths can run locklessly and concurrently, this leads to a data race. Furthermore, modifying tunnel->parms.o_flags permanently alters the tunnel configuration. To work around this, erspan_fill_info() (which reports config to userspace) was setting IP_TUNNEL_KEY_BIT back. If erspan_fill_info (running under RTNL) and erspan_xmit (running locklessly) race, erspan_xmit might see IP_TUNNEL_KEY_BIT set when it shouldn't, leading to GRE header corruption (injecting a key field into the ERSPAN GRE header). Fix this by: 1) Passing flags as an argument to __gre_xmit(). 2) Using local stack flags in ipgre_xmit(), gre_tap_xmit(), and erspan_xmit() to prevent TOCTOU data races with concurrent configuration updates, and passing them to __gre_xmit(). 3) Removing the racy modification of t->parms.o_flags in erspan_fill_info(). 4) Forcing IP_TUNNEL_KEY_BIT in the reported flags for ERSPAN locally in ipgre_fill_info(). For IPv6 ERSPAN: ip6erspan_tunnel_xmit() was locklessly clearing IP_TUNNEL_KEY_BIT in t->parms.o_flags even though it does not use these flags for building the GRE header (it uses local flags). This permanently corrupts the configuration and races with ip6gre_fill_info() which reads it. Remove the redundant and racy modification. This should remove false sharing in a fast path. Add const qualifiers in ipgre_fill_info(), erspan_fill_info() and ip6gre_fill_info() to clarify that these methods are not supposed to write any live parameters. Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Simon Horman <horms@kernel.org> Link: https://patch.msgid.link/20260812142257.21283-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>