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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Baul Lee , Ido Schimmel , Nikolay Aleksandrov , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com Subject: [PATCH net v2] vxlan: mdb: Fix use-after-free in vxlan_mdb_remote_src_del() Date: Thu, 27 Aug 2026 02:36:04 +0900 Message-ID: <20260826173604.90158-1-baul.lee@xbow.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vxlan_mdb_is_valid_source(), which validates MDBE_ATTR_SOURCE and every MDBE_ATTR_SRC_LIST member, accepts the all-zeros address. A source list is only accepted on a (*, G) entry, whose source is the all-zeros address, and for each member of the list an (S, G) entry is derived from it by substituting the source. Entries are keyed by a plain memcmp() of struct vxlan_mdb_entry_key, so if MDBE_ATTR_SOURCE is present and holds the all-zeros address and the source list holds it as well, the derived (S, G) key is byte-identical to the (*, G) key and resolves to the same entry. Omitting MDBE_ATTR_SOURCE is not equivalent, as the key is then left with a zero address family. vxlan_mdb_remote_src_del() removes the forwarding entry of a source before freeing the source entry: vxlan_mdb_remote_src_fwd_del(vxlan, group, remote, &ent->addr); vxlan_mdb_remote_src_entry_del(ent); With the keys aliased, the first call deletes the remote of the entry that owns 'ent' instead of a separate (S, G) entry, and frees 'ent'. The second call then runs on the freed entry, and its hlist_del() reads ->pprev and ->next out of it and writes through them. Adding the (*, G) entry with NLM_F_REPLACE and no source list marks the all-zeros source for deletion and reaches this from the sweep at the end of vxlan_mdb_remote_srcs_replace(). BUG: KASAN: slab-use-after-free in __vxlan_mdb_add+0x1cd/0xd70 Read of size 8 at addr ffff888102852500 by task poc/84 __vxlan_mdb_add+0x1cd/0xd70 vxlan_mdb_add+0xc0/0x140 rtnl_mdb_add+0x157/0x2a0 rtnetlink_rcv_msg+0x207/0x5a0 Allocated by task 84: __kmalloc_cache_noprof+0x153/0x360 vxlan_mdb_remote_srcs_add+0x2eb/0x440 __vxlan_mdb_add+0x803/0xd70 Freed by task 84: kfree+0x14c/0x3b0 vxlan_mdb_remote_del+0x129/0x1a0 __vxlan_mdb_del+0x4f/0xe0 vxlan_mdb_remote_src_fwd_del.isra.0+0x162/0x1b0 __vxlan_mdb_add+0x1c5/0xd70 The MDB operations are netns-scoped, so an unprivileged user can perform them in a new user and network namespace. Reject the all-zeros address in vxlan_mdb_is_valid_source(), which covers both call sites. A (*, G) entry is expressed by omitting the source, so nothing legitimate is refused. Discovered by XBOW, triaged by Baul Lee Fixes: a3a48de5eade ("vxlan: mdb: Add MDB control path support") Signed-off-by: Baul Lee --- Unrelated to [1]: different subsystem, different bug class, different fix site. It applies independently. v2: Use ipv4_is_zeronet(). Add test cases to star_g_common() and sg_common(). v1: https://lore.kernel.org/netdev/20260826151542.68815-1-baul.lee@xbow.com/ [1] https://lore.kernel.org/netdev/20260815172032.79740-1-baul.lee@xbow.com/ drivers/net/vxlan/vxlan_mdb.c | 8 ++++++++ tools/testing/selftests/net/test_vxlan_mdb.sh | 6 ++++++ 2 files changed, 14 insertions(+) diff --git a/drivers/net/vxlan/vxlan_mdb.c b/drivers/net/vxlan/vxlan_mdb.c index d71e1925ecfd..841f42ffecb9 100644 --- a/drivers/net/vxlan/vxlan_mdb.c +++ b/drivers/net/vxlan/vxlan_mdb.c @@ -354,6 +354,10 @@ static bool vxlan_mdb_is_valid_source(const struct nlattr *attr, __be16 proto, NL_SET_ERR_MSG_MOD(extack, "IPv4 multicast source address is not allowed"); return false; } + if (ipv4_is_zeronet(nla_get_in_addr(attr))) { + NL_SET_ERR_MSG_MOD(extack, "IPv4 all-zeros source address is not allowed"); + return false; + } break; #if IS_ENABLED(CONFIG_IPV6) case htons(ETH_P_IPV6): { @@ -368,6 +372,10 @@ static bool vxlan_mdb_is_valid_source(const struct nlattr *attr, __be16 proto, NL_SET_ERR_MSG_MOD(extack, "IPv6 multicast source address is not allowed"); return false; } + if (ipv6_addr_any(&src)) { + NL_SET_ERR_MSG_MOD(extack, "IPv6 all-zeros source address is not allowed"); + return false; + } break; } #endif diff --git a/tools/testing/selftests/net/test_vxlan_mdb.sh b/tools/testing/selftests/net/test_vxlan_mdb.sh index 58da5de99ac4..f9600aabd4a2 100755 --- a/tools/testing/selftests/net/test_vxlan_mdb.sh +++ b/tools/testing/selftests/net/test_vxlan_mdb.sh @@ -685,6 +685,9 @@ star_g_common() run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $grp permanent filter_mode exclude source_list $grp dst $vtep_ip src_vni 10010" log_test $? 255 "Invalid source in source list" + run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $grp permanent filter_mode exclude source_list $all_zeros_grp dst $vtep_ip src_vni 10010" + log_test $? 255 "All-zeros source in source list" + run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $grp permanent source_list $src1 dst $vtep_ip src_vni 10010" log_test $? 255 "Source list without filter mode" } @@ -784,6 +787,9 @@ sg_common() run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $grp src $grp permanent dst $vtep_ip src_vni 10010" log_test $? 255 "(S, G) with an invalid source list" + run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $grp src $all_zeros_grp permanent dst $vtep_ip src_vni 10010" + log_test $? 255 "(S, G) with an all-zeros source" + run_cmd "bridge -n $ns1 mdb add dev vx0 port vx0 grp $all_zeros_grp src $src permanent dst $vtep_ip src_vni 10010" log_test $? 255 "All-zeros group with source" }