When booting with the 'ipv6.disable=1' parameter, inet6_addr_lst
is never initialized because inet6_init() exits before addrconf_init()
is called to initialize it. An attempt to bind an RDS socket to
an ipv6 address results in a crash in __ipv6_chk_addr_and_flags()

KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
RIP: 0010:__ipv6_chk_addr_and_flags+0x1df/0x7e0
Call Trace:
 <TASK>
 ipv6_chk_addr+0x3b/0x50
 rds_tcp_laddr_check+0x155/0x3b0 [rds_tcp]
 rds_trans_get_preferred+0x15d/0x2d0 [rds]
 ? trace_hardirqs_on+0x2d/0x110
 rds_bind+0x1433/0x1d60 [rds]
 ? rds_remove_bound+0xd50/0xd50 [rds]
 ? aa_af_perm+0x250/0x250
 ? __might_fault+0xde/0x190
 ? __sys_bind+0x1dc/0x210
 __sys_bind+0x1dc/0x210
 ? __ia32_sys_socketpair+0x100/0x100
 ? restore_fpregs_from_fpstate+0x53/0x100
 __x64_sys_bind+0x73/0xb0
 ? syscall_enter_from_user_mode+0x1c/0x50
 do_syscall_64+0x34/0x80
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8
RIP: 0033:0x7f47f8269ea9
 </TASK>

The following code reproduces the issue:

struct sockaddr_in6 addr;
s = socket(PF_RDS, SOCK_SEQPACKET, 0);

memset(&addr, 0, sizeof(addr));
inet_pton(AF_INET6, ADDRESS, &addr.sin6_addr);
addr.sin6_family = AF_INET6;
addr.sin6_port = htons(PORT);

bind(s, &addr, sizeof(addr));

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with Syzkaller.

Fixes: eee2fa6ab322 ("rds: Changing IP address internal representation to struct in6_addr")
Fixes: 1e2b44e78eea ("rds: Enable RDS IPv6 support")
Signed-off-by: Ilia Gavrilov <redacted>
---
v2: Add a similar check for inbound link-local IPv6 connects

 net/rds/ib.c    | 4 ++++
 net/rds/ib_cm.c | 4 ++++
 net/rds/tcp.c   | 8 +++++---
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/rds/ib.c b/net/rds/ib.c
index 39f87272e071..8f9cf491984f 100644
--- a/net/rds/ib.c
+++ b/net/rds/ib.c

@@ -429,6 +429,10 @@ static int rds_ib_laddr_check_cm(struct net *net, const struct in6_addr *addr,
 		sa = (struct sockaddr *)&sin;
 	} else {
 #if IS_ENABLED(CONFIG_IPV6)
+		if (!ipv6_mod_enabled()) {
+			ret = -EADDRNOTAVAIL;
+			goto out;
+		}
 		memset(&sin6, 0, sizeof(sin6));
 		sin6.sin6_family = AF_INET6;
 		sin6.sin6_addr = *addr;

diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
index 5667f0173b47..d46146887ba4 100644
--- a/net/rds/ib_cm.c
+++ b/net/rds/ib_cm.c

@@ -810,6 +810,10 @@ int rds_ib_cm_handle_connect(struct rdma_cm_id *cm_id,
 	dp = event->param.conn.private_data;
 	if (isv6) {
 #if IS_ENABLED(CONFIG_IPV6)
+		if (!ipv6_mod_enabled()) {
+			err = -EOPNOTSUPP;
+			goto out;
+		}
 		dp_cmn = &dp->ricp_v6.dp_cmn;
 		saddr6 = &dp->ricp_v6.dp_saddr;
 		daddr6 = &dp->ricp_v6.dp_daddr;

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index a1de114d5e2e..955d92277d5a 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c

@@ -366,9 +366,11 @@ int rds_tcp_laddr_check(struct net *net, const struct in6_addr *addr,
 		rcu_read_unlock();
 	}
 #if IS_ENABLED(CONFIG_IPV6)
-	ret = ipv6_chk_addr(net, addr, dev, 0);
-	if (ret)
-		return 0;
+	if (ipv6_mod_enabled()) {
+		ret = ipv6_chk_addr(net, addr, dev, 0);
+		if (ret)
+			return 0;
+	}
 #endif
 	return -EADDRNOTAVAIL;
 }

-- 
2.47.3