vxlan: keep the last remote linked during FDB flush

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A non-nexthop FDB entry is expected to have at least one remote while it
remains reachable through the FDB hash table. A filtered bulk flush
violates this invariant when every remote matches: It unlinks the last
remote in vxlan_fdb_dst_destroy() and only afterwards tells vxlan_flush()
to destroy the parent FDB entry.

An RCU reader can find the parent during this interval.
first_remote_rcu() then applies list_entry_rcu() to the empty list head,
producing an invalid remote pointer that the receive learning path can
read from and write to.

When a matching remote is the sole remaining remote, leave it linked and
ask the caller to destroy the entire FDB entry. vxlan_fdb_destroy() keeps
the remote attached while sending the deletion notification and removing
the parent from the lookup structures.

Fixes: c499fccb71 ("vxlan: vxlan_core: Support FDB flushing by destination VNI")
Cc: stable@vger.kernel.org
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Co-developed-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: David Lee <david.lee@trailofbits.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260810144115.821654-1-david.lee@trailofbits.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Kyle Zeng 2026-08-10 14:41:14 +00:00 • committed by Jakub Kicinski

parent 87f21b59dd

commit d5d4a7b538

1 changed files with 5 additions and 4 deletions

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drivers/net/vxlan/vxlan_core.c

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