Re: [syzbot] [rdma?] KMSAN: uninit-value in ib_nl_handle_ip_res_resp

[Kohei Enju <enjuk@amazon.com>]

On Tue, 30 Sep 2025 13:29:32 -0700, syzbot wrote:

>Hello,
>
>syzbot found the following issue on:
>
>HEAD commit:    1896ce8eb6c6 Merge tag 'fsverity-for-linus' of git://git.k..
>git tree:       upstream
>console output: https://syzkaller.appspot.com/x/log.txt?x=153d0092580000
>kernel config:  https://syzkaller.appspot.com/x/.config?x=6eca10e0cdef44f
>dashboard link: https://syzkaller.appspot.com/bug?extid=938fcd548c303fe33c1a
>compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
>userspace arch: i386
>
>Unfortunately, I don't have any reproducer for this issue yet.
>
>Downloadable assets:
>disk image: https://storage.googleapis.com/syzbot-assets/d0fbab3c0b62/disk-1896ce8e.raw.xz
>vmlinux: https://storage.googleapis.com/syzbot-assets/71c7b444e106/vmlinux-1896ce8e.xz
>kernel image: https://storage.googleapis.com/syzbot-assets/96a4aa63999d/bzImage-1896ce8e.xz
>
>IMPORTANT: if you fix the issue, please add the following tag to the commit:
>Reported-by: syzbot+938fcd548c303fe33c1a@syzkaller.appspotmail.com
>
>netlink: 8 bytes leftover after parsing attributes in process `syz.8.3246'.
>=====================================================
>BUG: KMSAN: uninit-value in hex_byte_pack include/linux/hex.h:13 [inline]
>BUG: KMSAN: uninit-value in ip6_string+0xef4/0x13a0 lib/vsprintf.c:1490
> hex_byte_pack include/linux/hex.h:13 [inline]
> ip6_string+0xef4/0x13a0 lib/vsprintf.c:1490
> ip6_addr_string+0x18a/0x3e0 lib/vsprintf.c:1509
> ip_addr_string+0x245/0xee0 lib/vsprintf.c:1633
> pointer+0xc09/0x1bd0 lib/vsprintf.c:2542
> vsnprintf+0xf8a/0x1bd0 lib/vsprintf.c:2930
> vprintk_store+0x3ae/0x1530 kernel/printk/printk.c:2279
> vprintk_emit+0x307/0xcd0 kernel/printk/printk.c:2426
> vprintk_default+0x3f/0x50 kernel/printk/printk.c:2465
> vprintk+0x36/0x50 kernel/printk/printk_safe.c:82
> _printk+0x17e/0x1b0 kernel/printk/printk.c:2475
> ib_nl_process_good_ip_rsep drivers/infiniband/core/addr.c:128 [inline]

I see when gid is not initialized in nla_for_each_attr loop, this should
return early.

I think the splat occurrs when gid is not found, so a simple fix might
be like:

diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
index be0743dac3ff..c03a308bcda5 100644
--- a/drivers/infiniband/core/addr.c
+++ b/drivers/infiniband/core/addr.c
@@ -103,15 +103,21 @@ static void ib_nl_process_good_ip_rsep(const struct nlmsghdr *nlh)
        struct addr_req *req;
        int len, rem;
        int found = 0;
+       bool gid_found = false;

        head = (const struct nlattr *)nlmsg_data(nlh);
        len = nlmsg_len(nlh);

        nla_for_each_attr(curr, head, len, rem) {
-               if (curr->nla_type == LS_NLA_TYPE_DGID)
+               if (curr->nla_type == LS_NLA_TYPE_DGID) {
                        memcpy(&gid, nla_data(curr), nla_len(curr));
+                       gid_found = true;
+               }
        }

+       if (!gid_found)
+               return;
+
        spin_lock_bh(&lock);
        list_for_each_entry(req, &req_list, list) {
                if (nlh->nlmsg_seq != req->seq)

> ib_nl_handle_ip_res_resp+0x963/0x9d0 drivers/infiniband/core/addr.c:141
> rdma_nl_rcv_msg drivers/infiniband/core/netlink.c:-1 [inline]
> rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
> rdma_nl_rcv+0xefa/0x11c0 drivers/infiniband/core/netlink.c:259
> netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
> netlink_unicast+0xf04/0x12b0 net/netlink/af_netlink.c:1346
> netlink_sendmsg+0x10b3/0x1250 net/netlink/af_netlink.c:1896
> sock_sendmsg_nosec net/socket.c:714 [inline]
> __sock_sendmsg+0x333/0x3d0 net/socket.c:729
> ____sys_sendmsg+0x7e0/0xd80 net/socket.c:2617
> ___sys_sendmsg+0x271/0x3b0 net/socket.c:2671
> __sys_sendmsg+0x1aa/0x300 net/socket.c:2703
> __compat_sys_sendmsg net/compat.c:346 [inline]
> __do_compat_sys_sendmsg net/compat.c:353 [inline]
> __se_compat_sys_sendmsg net/compat.c:350 [inline]
> __ia32_compat_sys_sendmsg+0xa4/0x100 net/compat.c:350
> ia32_sys_call+0x3f6c/0x4310 arch/x86/include/generated/asm/syscalls_32.h:371
> do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
> __do_fast_syscall_32+0xb0/0x150 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
>
>Local variable gid.i created at:
> ib_nl_process_good_ip_rsep drivers/infiniband/core/addr.c:102 [inline]
> ib_nl_handle_ip_res_resp+0x254/0x9d0 drivers/infiniband/core/addr.c:141
> rdma_nl_rcv_msg drivers/infiniband/core/netlink.c:-1 [inline]
> rdma_nl_rcv_skb drivers/infiniband/core/netlink.c:239 [inline]
> rdma_nl_rcv+0xefa/0x11c0 drivers/infiniband/core/netlink.c:259
>
>CPU: 0 UID: 0 PID: 17455 Comm: syz.8.3246 Not tainted syzkaller #0 PREEMPT(none) 
>Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
>=====================================================
>
>
>---
>This report is generated by a bot. It may contain errors.
>See https://goo.gl/tpsmEJ for more information about syzbot.
>syzbot engineers can be reached at syzkaller@googlegroups.com.
>
>syzbot will keep track of this issue. See:
>https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
>If the report is already addressed, let syzbot know by replying with:
>#syz fix: exact-commit-title
>
>If you want to overwrite report's subsystems, reply with:
>#syz set subsystems: new-subsystem
>(See the list of subsystem names on the web dashboard)
>
>If the report is a duplicate of another one, reply with:
>#syz dup: exact-subject-of-another-report
>
>If you want to undo deduplication, reply with:
>#syz undup
>