Patch "ipv4: Fix uninit-value access in __ip_make_skb()" has been added to the 6.8-stable tree

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This is a note to let you know that I've just added the patch titled

    ipv4: Fix uninit-value access in __ip_make_skb()

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipv4-fix-uninit-value-access-in-__ip_make_skb.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ac87f09af0049fbd60a080ba68d42965f8d7134a
Author: Shigeru Yoshida <syoshida@xxxxxxxxxx>
Date:   Tue Apr 30 21:39:45 2024 +0900

    ipv4: Fix uninit-value access in __ip_make_skb()
    
    [ Upstream commit fc1092f51567277509563800a3c56732070b6aa4 ]
    
    KMSAN reported uninit-value access in __ip_make_skb() [1].  __ip_make_skb()
    tests HDRINCL to know if the skb has icmphdr. However, HDRINCL can cause a
    race condition. If calling setsockopt(2) with IP_HDRINCL changes HDRINCL
    while __ip_make_skb() is running, the function will access icmphdr in the
    skb even if it is not included. This causes the issue reported by KMSAN.
    
    Check FLOWI_FLAG_KNOWN_NH on fl4->flowi4_flags instead of testing HDRINCL
    on the socket.
    
    Also, fl4->fl4_icmp_type and fl4->fl4_icmp_code are not initialized. These
    are union in struct flowi4 and are implicitly initialized by
    flowi4_init_output(), but we should not rely on specific union layout.
    
    Initialize these explicitly in raw_sendmsg().
    
    [1]
    BUG: KMSAN: uninit-value in __ip_make_skb+0x2b74/0x2d20 net/ipv4/ip_output.c:1481
     __ip_make_skb+0x2b74/0x2d20 net/ipv4/ip_output.c:1481
     ip_finish_skb include/net/ip.h:243 [inline]
     ip_push_pending_frames+0x4c/0x5c0 net/ipv4/ip_output.c:1508
     raw_sendmsg+0x2381/0x2690 net/ipv4/raw.c:654
     inet_sendmsg+0x27b/0x2a0 net/ipv4/af_inet.c:851
     sock_sendmsg_nosec net/socket.c:730 [inline]
     __sock_sendmsg+0x274/0x3c0 net/socket.c:745
     __sys_sendto+0x62c/0x7b0 net/socket.c:2191
     __do_sys_sendto net/socket.c:2203 [inline]
     __se_sys_sendto net/socket.c:2199 [inline]
     __x64_sys_sendto+0x130/0x200 net/socket.c:2199
     do_syscall_64+0xd8/0x1f0 arch/x86/entry/common.c:83
     entry_SYSCALL_64_after_hwframe+0x6d/0x75
    
    Uninit was created at:
     slab_post_alloc_hook mm/slub.c:3804 [inline]
     slab_alloc_node mm/slub.c:3845 [inline]
     kmem_cache_alloc_node+0x5f6/0xc50 mm/slub.c:3888
     kmalloc_reserve+0x13c/0x4a0 net/core/skbuff.c:577
     __alloc_skb+0x35a/0x7c0 net/core/skbuff.c:668
     alloc_skb include/linux/skbuff.h:1318 [inline]
     __ip_append_data+0x49ab/0x68c0 net/ipv4/ip_output.c:1128
     ip_append_data+0x1e7/0x260 net/ipv4/ip_output.c:1365
     raw_sendmsg+0x22b1/0x2690 net/ipv4/raw.c:648
     inet_sendmsg+0x27b/0x2a0 net/ipv4/af_inet.c:851
     sock_sendmsg_nosec net/socket.c:730 [inline]
     __sock_sendmsg+0x274/0x3c0 net/socket.c:745
     __sys_sendto+0x62c/0x7b0 net/socket.c:2191
     __do_sys_sendto net/socket.c:2203 [inline]
     __se_sys_sendto net/socket.c:2199 [inline]
     __x64_sys_sendto+0x130/0x200 net/socket.c:2199
     do_syscall_64+0xd8/0x1f0 arch/x86/entry/common.c:83
     entry_SYSCALL_64_after_hwframe+0x6d/0x75
    
    CPU: 1 PID: 15709 Comm: syz-executor.7 Not tainted 6.8.0-11567-gb3603fcb79b1 #25
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
    
    Fixes: 99e5acae193e ("ipv4: Fix potential uninit variable access bug in __ip_make_skb()")
    Reported-by: syzkaller <syzkaller@xxxxxxxxxxxxxxxx>
    Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240430123945.2057348-1-syoshida@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 67d846622365e..a38e63669c54a 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1473,7 +1473,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
 		 * by icmp_hdr(skb)->type.
 		 */
 		if (sk->sk_type == SOCK_RAW &&
-		    !inet_test_bit(HDRINCL, sk))
+		    !(fl4->flowi4_flags & FLOWI_FLAG_KNOWN_NH))
 			icmp_type = fl4->fl4_icmp_type;
 		else
 			icmp_type = icmp_hdr(skb)->type;
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 288f1846b3518..a1d8218fa1a2d 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -605,6 +605,9 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			    (hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
 			   daddr, saddr, 0, 0, sk->sk_uid);
 
+	fl4.fl4_icmp_type = 0;
+	fl4.fl4_icmp_code = 0;
+
 	if (!hdrincl) {
 		rfv.msg = msg;
 		rfv.hlen = 0;




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