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KASAN: use-after-free Read in ip_skb_dst_mtu

Status: premoderation: reported on 2025/10/27 00:09
Reported-by: syzbot+c3edeb29ac035fdf2d48@syzkaller.appspotmail.com
First crash: 7d07h, last: 7d07h
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Read in ip_skb_dst_mtu origin:upstream 19 C inconclusive 2 520d 626d 0/3 auto-obsoleted due to no activity on 2024/12/14 20:26
upstream KASAN: slab-use-after-free Read in ip_skb_dst_mtu (2) bcachefs net 19 syz done 1 246d 240d 0/29 auto-obsoleted due to no activity on 2025/06/09 18:32
upstream KASAN: slab-use-after-free Read in ip_skb_dst_mtu netfilter 19 C error 5 575d 606d 25/29 fixed on 2024/05/22 23:56

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ip_dst_mtu_maybe_forward include/net/ip.h:472 [inline]
BUG: KASAN: use-after-free in ip_skb_dst_mtu+0x58e/0x630 include/net/ip.h:493
Read of size 4 at addr ffff88812aa580d8 by task syz.0.10105/4366

CPU: 1 PID: 4366 Comm: syz.0.10105 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0xf1/0x140 mm/kasan/report.c:444
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ip_dst_mtu_maybe_forward include/net/ip.h:472 [inline]
 ip_skb_dst_mtu+0x58e/0x630 include/net/ip.h:493
 __ip_finish_output+0xd4/0x360 net/ipv4/ip_output.c:299
 ip_finish_output+0x31/0x240 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip_output+0x1e1/0x360 net/ipv4/ip_output.c:430
 dst_output include/net/dst.h:453 [inline]
 ip_local_out net/ipv4/ip_output.c:126 [inline]
 ip_send_skb+0xb2/0x140 net/ipv4/ip_output.c:1581
 udp_send_skb+0x938/0x1240 net/ipv4/udp.c:991
 udp_sendmsg+0x173d/0x20b0 net/ipv4/udp.c:1279
 inet_sendmsg+0xa5/0xc0 net/ipv4/af_inet.c:830
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 ____sys_sendmsg+0x5a2/0x8c0 net/socket.c:2436
 ___sys_sendmsg+0x1f0/0x260 net/socket.c:2490
 __sys_sendmmsg+0x278/0x480 net/socket.c:2576
 __do_sys_sendmmsg net/socket.c:2605 [inline]
 __se_sys_sendmmsg net/socket.c:2602 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2602
 x64_sys_call+0x6c6/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc203c20fc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc202689038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007fc203e77fa0 RCX: 00007fc203c20fc9
RDX: 000000000800001d RSI: 0000200000007fc0 RDI: 0000000000000008
RBP: 00007fc203ca3f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc203e78038 R14: 00007fc203e77fa0 R15: 00007ffe6b907338
 </TASK>

The buggy address belongs to the page:
page:ffffea0004aa9600 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12aa58
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea00053f5a08 ffff8881f713c5f0 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x546dc0(GFP_USER|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP|__GFP_ZERO|__GFP_ACCOUNT), pid 30403, ts 1395237664953, free_ts 1699526322027
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
 get_page_from_freelist+0x2cc5/0x2d50 mm/page_alloc.c:4485
 __alloc_pages+0x18f/0x440 mm/page_alloc.c:5808
 __alloc_pages_node include/linux/gfp.h:595 [inline]
 alloc_pages_node include/linux/gfp.h:609 [inline]
 alloc_pages include/linux/gfp.h:622 [inline]
 kmalloc_order+0x4c/0x160 mm/slab_common.c:995
 kmalloc_order_trace+0x18/0xb0 mm/slab_common.c:1014
 kmalloc_large include/linux/slab.h:548 [inline]
 __kmalloc+0x199/0x2c0 mm/slub.c:4425
 __kmalloc_node include/linux/slab.h:487 [inline]
 kmalloc_node include/linux/slab.h:642 [inline]
 kvmalloc_node+0x206/0x300 mm/util.c:621
 kvmalloc include/linux/mm.h:862 [inline]
 kvzalloc include/linux/mm.h:870 [inline]
 alloc_netdev_mqs+0x8d/0xc90 net/core/dev.c:10900
 tun_set_iff+0x535/0xe00 drivers/net/tun.c:2773
 __tun_chr_ioctl+0x7e8/0x1eb0 drivers/net/tun.c:3062
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:3349
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:860
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
 x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1472 [inline]
 free_pcp_prepare mm/page_alloc.c:1544 [inline]
 free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
 free_unref_page+0xa2/0x550 mm/page_alloc.c:3616
 free_the_page mm/page_alloc.c:805 [inline]
 __free_pages+0x6c/0x100 mm/page_alloc.c:5884
 free_nonslab_page+0x86/0xc0 mm/slub.c:3564
 kfree+0x19a/0x270 mm/slub.c:4585
 kvfree+0x35/0x40 mm/util.c:661
 netdev_freemem+0x3f/0x60 net/core/dev.c:10854
 netdev_release+0x7f/0xb0 net/core/net-sysfs.c:1903
 device_release+0x96/0x1c0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:713 [inline]
 kobject_release lib/kobject.c:744 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x18a/0x270 lib/kobject.c:761
 netdev_run_todo+0x812/0x990 net/core/dev.c:10710
 rtnl_unlock net/core/rtnetlink.c:112 [inline]
 rtnetlink_rcv_msg+0xa1d/0xb90 net/core/rtnetlink.c:5651
 netlink_rcv_skb+0x1e0/0x430 net/netlink/af_netlink.c:2511
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5668
 netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
 netlink_unicast+0x876/0xa40 net/netlink/af_netlink.c:1348
 netlink_sendmsg+0x86a/0xb70 net/netlink/af_netlink.c:1922

Memory state around the buggy address:
 ffff88812aa57f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88812aa58000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812aa58080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                    ^
 ffff88812aa58100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812aa58180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/27 00:08 android13-5.15-lts 1edb21e89ce4 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in ip_skb_dst_mtu
* Struck through repros no longer work on HEAD.