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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>
This commit is contained in:
Kyle Zeng
2026-08-10 14:41:14 +00:00
committed by Jakub Kicinski
parent 87f21b59dd
commit d5d4a7b538
1 changed files with 6 additions and 5 deletions
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11
drivers/net/vxlan/vxlan_core.c
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@@ -3058,18 +3058,19 @@ vxlan_fdb_flush_match_remotes(struct vxlan_fdb *f, struct vxlan_dev *vxlan,
const struct vxlan_fdb_flush_desc *desc,
bool *p_destroy_fdb)
{
bool remotes_flushed = false;
struct vxlan_rdst *rd, *tmp;
list_for_each_entry_safe(rd, tmp, &f->remotes, list) {
if (!vxlan_fdb_flush_remote_matches(desc, rd))
continue;
vxlan_fdb_dst_destroy(vxlan, f, rd, true);
remotes_flushed = true;
}
if (list_is_singular(&f->remotes)) {
*p_destroy_fdb = true;
return;
}
*p_destroy_fdb = remotes_flushed && list_empty(&f->remotes);
vxlan_fdb_dst_destroy(vxlan, f, rd, true);
}
}
/* Purge the forwarding table */