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ipvs: fix uninit-value for saddr in do_output_route4
JIRA: https://issues.redhat.com/browse/RHEL-115630 Upstream Status: commit e34090d commit e34090d Author: Julian Anastasov <ja@ssi.bg> Date: Sat May 3 01:01:18 2025 +0300 ipvs: fix uninit-value for saddr in do_output_route4 syzbot reports for uninit-value for the saddr argument [1]. commit 4754957 ("ipvs: do not use random local source address for tunnels") already implies that the input value of saddr should be ignored but the code is still reading it which can prevent to connect the route. Fix it by changing the argument to ret_saddr. [1] BUG: KMSAN: uninit-value in do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147 do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147 __ip_vs_get_out_rt+0x403/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:330 ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136 ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626 nf_hook include/linux/netfilter.h:269 [inline] __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118 ip_local_out net/ipv4/ip_output.c:127 [inline] ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501 udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195 udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483 inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x267/0x380 net/socket.c:727 ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620 __sys_sendmmsg+0x41d/0x880 net/socket.c:2702 __compat_sys_sendmmsg net/compat.c:360 [inline] __do_compat_sys_sendmmsg net/compat.c:367 [inline] __se_compat_sys_sendmmsg net/compat.c:364 [inline] __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364 ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369 entry_SYSENTER_compat_after_hwframe+0x84/0x8e Uninit was created at: slab_post_alloc_hook mm/slub.c:4167 [inline] slab_alloc_node mm/slub.c:4210 [inline] __kmalloc_cache_noprof+0x8fa/0xe00 mm/slub.c:4367 kmalloc_noprof include/linux/slab.h:905 [inline] ip_vs_dest_dst_alloc net/netfilter/ipvs/ip_vs_xmit.c:61 [inline] __ip_vs_get_out_rt+0x35d/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:323 ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136 ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626 nf_hook include/linux/netfilter.h:269 [inline] __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118 ip_local_out net/ipv4/ip_output.c:127 [inline] ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501 udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195 udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483 inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x267/0x380 net/socket.c:727 ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620 __sys_sendmmsg+0x41d/0x880 net/socket.c:2702 __compat_sys_sendmmsg net/compat.c:360 [inline] __do_compat_sys_sendmmsg net/compat.c:367 [inline] __se_compat_sys_sendmmsg net/compat.c:364 [inline] __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364 ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369 entry_SYSENTER_compat_after_hwframe+0x84/0x8e CPU: 0 UID: 0 PID: 22408 Comm: syz.4.5165 Not tainted 6.15.0-rc3-syzkaller-00019-gbc3372351d0c #0 PREEMPT(undef) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 Reported-by: syzbot+04b9a82855c8aed20860@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68138dfa.050a0220.14dd7d.0017.GAE@google.com/ Fixes: 4754957 ("ipvs: do not use random local source address for tunnels") Signed-off-by: Julian Anastasov <ja@ssi.bg> Acked-by: Simon Horman <horms@kernel.org> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Conflicts: - net/netfilter/ipvs/ip_vs_xmit.c: 1 hunk modified RHEL9 lacks 3f06760 ("ipv4: Drop tos parameter from flowi4_update_output()") so the function expects 5 arguments, not 4 as in upstream. Assisted-by: Patchpal AI Signed-off-by: Florian Westphal <fwestpha@redhat.com>
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‎net/netfilter/ipvs/ip_vs_xmit.c‎

Lines changed: 8 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -119,13 +119,12 @@ __mtu_check_toobig_v6(const struct sk_buff *skb, u32 mtu)
119119
return false;
120120
}
121121

122-
/* Get route to daddr, update *saddr, optionally bind route to saddr */
122+
/* Get route to daddr, optionally bind route to saddr */
123123
static struct rtable *do_output_route4(struct net *net, __be32 daddr,
124-
int rt_mode, __be32 *saddr)
124+
int rt_mode, __be32 *ret_saddr)
125125
{
126126
struct flowi4 fl4;
127127
struct rtable *rt;
128-
bool loop = false;
129128

130129
memset(&fl4, 0, sizeof(fl4));
131130
fl4.daddr = daddr;
@@ -135,23 +134,17 @@ static struct rtable *do_output_route4(struct net *net, __be32 daddr,
135134
retry:
136135
rt = ip_route_output_key(net, &fl4);
137136
if (IS_ERR(rt)) {
138-
/* Invalid saddr ? */
139-
if (PTR_ERR(rt) == -EINVAL && *saddr &&
140-
rt_mode & IP_VS_RT_MODE_CONNECT && !loop) {
141-
*saddr = 0;
142-
flowi4_update_output(&fl4, 0, 0, daddr, 0);
143-
goto retry;
144-
}
145137
IP_VS_DBG_RL("ip_route_output error, dest: %pI4\n", &daddr);
146138
return NULL;
147-
} else if (!*saddr && rt_mode & IP_VS_RT_MODE_CONNECT && fl4.saddr) {
139+
}
140+
if (rt_mode & IP_VS_RT_MODE_CONNECT && fl4.saddr) {
148141
ip_rt_put(rt);
149-
*saddr = fl4.saddr;
150142
flowi4_update_output(&fl4, 0, 0, daddr, fl4.saddr);
151-
loop = true;
143+
rt_mode = 0;
152144
goto retry;
153145
}
154-
*saddr = fl4.saddr;
146+
if (ret_saddr)
147+
*ret_saddr = fl4.saddr;
155148
return rt;
156149
}
157150

@@ -344,19 +337,15 @@ __ip_vs_get_out_rt(struct netns_ipvs *ipvs, int skb_af, struct sk_buff *skb,
344337
if (ret_saddr)
345338
*ret_saddr = dest_dst->dst_saddr.ip;
346339
} else {
347-
__be32 saddr = htonl(INADDR_ANY);
348-
349340
noref = 0;
350341

351342
/* For such unconfigured boxes avoid many route lookups
352343
* for performance reasons because we do not remember saddr
353344
*/
354345
rt_mode &= ~IP_VS_RT_MODE_CONNECT;
355-
rt = do_output_route4(net, daddr, rt_mode, &saddr);
346+
rt = do_output_route4(net, daddr, rt_mode, ret_saddr);
356347
if (!rt)
357348
goto err_unreach;
358-
if (ret_saddr)
359-
*ret_saddr = saddr;
360349
}
361350

362351
local = (rt->rt_flags & RTCF_LOCAL) ? 1 : 0;

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