linux-kernel - [syzbot] [net?] memory leak in __build

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Message-ID: <6965534b.050a0220.38aacd.0001.GAE@google.com>
Date: Mon, 12 Jan 2026 12:02:19 -0800
From: syzbot <syzbot+4d8c7d16b0e95c0d0f0d@...kaller.appspotmail.com>
To: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, 
	jasowang@...hat.com, kuba@...nel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, pabeni@...hat.com, syzkaller-bugs@...glegroups.com, 
	willemdebruijn.kernel@...il.com
Subject: [syzbot] [net?] memory leak in __build_skb (4)

Hello,

syzbot found the following issue on:

HEAD commit:    623fb9912f6a Merge tag 'pinctrl-v6.19-2' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=149a1922580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d60836e327fd6756
dashboard link: https://syzkaller.appspot.com/bug?extid=4d8c7d16b0e95c0d0f0d
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=137fb1fc580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14c0519a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a5d95462c1e9/disk-623fb991.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0305879ad943/vmlinux-623fb991.xz
kernel image: https://storage.googleapis.com/syzbot-assets/98136e3b98e4/bzImage-623fb991.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4d8c7d16b0e95c0d0f0d@...kaller.appspotmail.com

BUG: memory leak
unreferenced object 0xffff888109695a00 (size 240):
  comm "syz.0.17", pid 6088, jiffies 4294943096
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc a84b336f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881037b5e40 (size 192):
  comm "syz.0.17", pid 6088, jiffies 4294943096
  hex dump (first 32 bytes):
    00 40 9c 26 81 88 ff ff c0 66 0b 87 ff ff ff ff  .@.......f......
    21 52 bc 85 ff ff ff ff 00 00 00 00 00 00 00 00  !R..............
  backtrace (crc fcd1b1c6):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    dst_alloc+0x5b/0xe0 net/core/dst.c:89
    rt_dst_alloc+0x32/0xe0 net/ipv4/route.c:1651
    ip_route_input_slow+0xaa0/0x1560 net/ipv4/route.c:2429
    ip_route_input_rcu net/ipv4/route.c:2543 [inline]
    ip_route_input_noref+0xd1/0xe0 net/ipv4/route.c:2554
    ip_rcv_finish_core+0xca/0x7f0 net/ipv4/ip_input.c:368
    ip_rcv_finish net/ipv4/ip_input.c:451 [inline]
    NF_HOOK include/linux/netfilter.h:318 [inline]
    NF_HOOK include/linux/netfilter.h:312 [inline]
    ip_rcv+0x197/0x240 net/ipv4/ip_input.c:573
    __netif_receive_skb_one_core+0xd0/0x100 net/core/dev.c:6139
    __netif_receive_skb+0x1d/0x80 net/core/dev.c:6252
    netif_receive_skb_internal net/core/dev.c:6338 [inline]
    netif_receive_skb+0x49/0x240 net/core/dev.c:6397
    tun_rx_batched drivers/net/tun.c:1485 [inline]
    tun_get_user+0x1dbf/0x2030 drivers/net/tun.c:1953
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff8881095d2200 (size 240):
  comm "syz.0.18", pid 6092, jiffies 4294943097
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc e1df1ba8):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff888109688800 (size 240):
  comm "syz.0.19", pid 6094, jiffies 4294943098
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace (crc 4b7eec9d):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270
    __build_skb+0x23/0x60 net/core/skbuff.c:474
    build_skb+0x20/0x190 net/core/skbuff.c:490
    __tun_build_skb drivers/net/tun.c:1541 [inline]
    tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636
    tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770
    tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999
    new_sync_write fs/read_write.c:593 [inline]
    vfs_write+0x45d/0x710 fs/read_write.c:686
    ksys_write+0xa7/0x170 fs/read_write.c:738
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF


---
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