Re: [syzbot] [net?] KASAN: use-after-free Read in __skb_flow_dissect (3)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in __skb_flow_dissect

==================================================================
BUG: KASAN: use-after-free in __skb_flow_dissect+0x1992/0x7b60 net/core/flow_dissector.c:1170
Read of size 1 at addr ffff888124e0000e by task syz-executor.0/5476

CPU: 1 PID: 5476 Comm: syz-executor.0 Not tainted 6.7.0-syzkaller-g9d1694dc91ce-dirty #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0xc4/0x620 mm/kasan/report.c:488
 kasan_report+0xda/0x110 mm/kasan/report.c:601
 __skb_flow_dissect+0x1992/0x7b60 net/core/flow_dissector.c:1170
 skb_flow_dissect_flow_keys include/linux/skbuff.h:1524 [inline]
 ___skb_get_hash net/core/flow_dissector.c:1795 [inline]
 __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1860
 skb_get_hash include/linux/skbuff.h:1566 [inline]
 ip_tunnel_xmit+0x1843/0x33b0 net/ipv4/ip_tunnel.c:748
 ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308
 __netdev_start_xmit include/linux/netdevice.h:4989 [inline]
 netdev_start_xmit include/linux/netdevice.h:5003 [inline]
 xmit_one net/core/dev.c:3547 [inline]
 dev_hard_start_xmit+0x137/0x6d0 net/core/dev.c:3563
 __dev_queue_xmit+0x7b6/0x3ed0 net/core/dev.c:4351
 dev_queue_xmit include/linux/netdevice.h:3171 [inline]
 neigh_connected_output+0x426/0x5d0 net/core/neighbour.c:1592
 neigh_output include/net/neighbour.h:542 [inline]
 ip_finish_output2+0x82d/0x2540 net/ipv4/ip_output.c:235
 __ip_finish_output net/ipv4/ip_output.c:313 [inline]
 __ip_finish_output+0x38b/0x650 net/ipv4/ip_output.c:295
 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323
 NF_HOOK_COND include/linux/netfilter.h:303 [inline]
 ip_mc_output+0x1dd/0x6a0 net/ipv4/ip_output.c:420
 dst_output include/net/dst.h:451 [inline]
 ip_local_out+0xaf/0x1a0 net/ipv4/ip_output.c:129
 iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82
 ip_tunnel_xmit+0x1daa/0x33b0 net/ipv4/ip_tunnel.c:831
 ipgre_xmit+0x49b/0x980 net/ipv4/ip_gre.c:665
 __netdev_start_xmit include/linux/netdevice.h:4989 [inline]
 netdev_start_xmit include/linux/netdevice.h:5003 [inline]
 xmit_one net/core/dev.c:3547 [inline]
 dev_hard_start_xmit+0x137/0x6d0 net/core/dev.c:3563
 __dev_queue_xmit+0x7b6/0x3ed0 net/core/dev.c:4351
 dev_queue_xmit include/linux/netdevice.h:3171 [inline]
 __bpf_tx_skb net/core/filter.c:2135 [inline]
 __bpf_redirect_no_mac net/core/filter.c:2165 [inline]
 __bpf_redirect+0x6f1/0xf10 net/core/filter.c:2188
 ____bpf_clone_redirect net/core/filter.c:2459 [inline]
 bpf_clone_redirect+0x2b2/0x420 net/core/filter.c:2431
 ___bpf_prog_run+0x3e44/0xabc0 kernel/bpf/core.c:1986
 __bpf_prog_run512+0xb7/0xf0 kernel/bpf/core.c:2227
 bpf_dispatcher_nop_func include/linux/bpf.h:1231 [inline]
 __bpf_prog_run include/linux/filter.h:651 [inline]
 bpf_prog_run include/linux/filter.h:658 [inline]
 bpf_test_run+0x3d3/0x9c0 net/bpf/test_run.c:423
 bpf_prog_test_run_skb+0xb75/0x1dd0 net/bpf/test_run.c:1056
 bpf_prog_test_run kernel/bpf/syscall.c:4107 [inline]
 __sys_bpf+0x11bf/0x4a00 kernel/bpf/syscall.c:5475
 __do_sys_bpf kernel/bpf/syscall.c:5561 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5559 [inline]
 __x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5559
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xd3/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f36b107cce9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f36b1e270c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f36b119bf80 RCX: 00007f36b107cce9
RDX: 0000000000000028 RSI: 0000000020000080 RDI: 000000000000000a
RBP: 00007f36b10c947a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f36b119bf80 R15: 00007ffcb895ffc8
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0004938000 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x124e00
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 057ff00000000000 ffffea0004938008 ffffea0004938008 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff888124dfff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888124dfff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888124e00000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff888124e00080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888124e00100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         9d1694dc Merge tag 'for-6.8/block-2024-01-18' of git:/..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=11c3d5afe80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=70f4213b9a7b4f3a
dashboard link: https://syzkaller.appspot.com/bug?extid=bfde3bef047a81b8fde6
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13c7c2abe80000