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syzbot found a use-after-free in inet6_mc_check [1] The problem here is that inet6_mc_check() uses rcu and read_lock(&iml->sflock) So the fact that ip6_mc_leave_src() is called under RTNL and the socket lock does not help us, we need to acquire iml->sflock in write mode. In the future, we should convert all this stuff to RCU. [1] BUG: KASAN: use-after-free in ipv6_addr_equal include/net/ipv6.h:521 [inline] BUG: KASAN: use-after-free in inet6_mc_check+0xae7/0xb40 net/ipv6/mcast.c:649 Read of size 8 at addr ffff8801ce7f2510 by task syz-executor0/22432 CPU: 1 PID: 22432 Comm: syz-executor0 Not tainted 4.19.0-rc7+ #280 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 ipv6_addr_equal include/net/ipv6.h:521 [inline] inet6_mc_check+0xae7/0xb40 net/ipv6/mcast.c:649 __raw_v6_lookup+0x320/0x3f0 net/ipv6/raw.c:98 ipv6_raw_deliver net/ipv6/raw.c:183 [inline] raw6_local_deliver+0x3d3/0xcb0 net/ipv6/raw.c:240 ip6_input_finish+0x467/0x1aa0 net/ipv6/ip6_input.c:345 NF_HOOK include/linux/netfilter.h:289 [inline] ip6_input+0xe9/0x600 net/ipv6/ip6_input.c:426 ip6_mc_input+0x48a/0xd20 net/ipv6/ip6_input.c:503 dst_input include/net/dst.h:450 [inline] ip6_rcv_finish+0x17a/0x330 net/ipv6/ip6_input.c:76 NF_HOOK include/linux/netfilter.h:289 [inline] ipv6_rcv+0x120/0x640 net/ipv6/ip6_input.c:271 __netif_receive_skb_one_core+0x14d/0x200 net/core/dev.c:4913 __netif_receive_skb+0x2c/0x1e0 net/core/dev.c:5023 netif_receive_skb_internal+0x12c/0x620 net/core/dev.c:5126 napi_frags_finish net/core/dev.c:5664 [inline] napi_gro_frags+0x75a/0xc90 net/core/dev.c:5737 tun_get_user+0x3189/0x4250 drivers/net/tun.c:1923 tun_chr_write_iter+0xb9/0x154 drivers/net/tun.c:1968 call_write_iter include/linux/fs.h:1808 [inline] do_iter_readv_writev+0x8b0/0xa80 fs/read_write.c:680 do_iter_write+0x185/0x5f0 fs/read_write.c:959 vfs_writev+0x1f1/0x360 fs/read_write.c:1004 do_writev+0x11a/0x310 fs/read_write.c:1039 __do_sys_writev fs/read_write.c:1112 [inline] __se_sys_writev fs/read_write.c:1109 [inline] __x64_sys_writev+0x75/0xb0 fs/read_write.c:1109 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457421 Code: 75 14 b8 14 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 b5 fb ff c3 48 83 ec 08 e8 1a 2d 00 00 48 89 04 24 b8 14 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 63 2d 00 00 48 89 d0 48 83 c4 08 48 3d 01 RSP: 002b:00007f2d30ecaba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014 RAX: ffffffffffffffda RBX: 000000000000003e RCX: 0000000000457421 RDX: 0000000000000001 RSI: 00007f2d30ecabf0 RDI: 00000000000000f0 RBP: 0000000020000500 R08: 00000000000000f0 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000293 R12: 00007f2d30ecb6d4 R13: 00000000004c4890 R14: 00000000004d7b90 R15: 00000000ffffffff Allocated by task 22437: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 __do_kmalloc mm/slab.c:3718 [inline] __kmalloc+0x14e/0x760 mm/slab.c:3727 kmalloc include/linux/slab.h:518 [inline] sock_kmalloc+0x15a/0x1f0 net/core/sock.c:1983 ip6_mc_source+0x14dd/0x1960 net/ipv6/mcast.c:427 do_ipv6_setsockopt.isra.9+0x3afb/0x45d0 net/ipv6/ipv6_sockglue.c:743 ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:933 rawv6_setsockopt+0x59/0x140 net/ipv6/raw.c:1069 sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3038 __sys_setsockopt+0x1ba/0x3c0 net/socket.c:1902 __do_sys_setsockopt net/socket.c:1913 [inline] __se_sys_setsockopt net/socket.c:1910 [inline] __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1910 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 22430: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3498 [inline] kfree+0xcf/0x230 mm/slab.c:3813 __sock_kfree_s net/core/sock.c:2004 [inline] sock_kfree_s+0x29/0x60 net/core/sock.c:2010 ip6_mc_leave_src+0x11a/0x1d0 net/ipv6/mcast.c:2448 __ipv6_sock_mc_close+0x20b/0x4e0 net/ipv6/mcast.c:310 ipv6_sock_mc_close+0x158/0x1d0 net/ipv6/mcast.c:328 inet6_release+0x40/0x70 net/ipv6/af_inet6.c:452 __sock_release+0xd7/0x250 net/socket.c:579 sock_close+0x19/0x20 net/socket.c:1141 __fput+0x385/0xa30 fs/file_table.c:278 ____fput+0x15/0x20 fs/file_table.c:309 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:193 [inline] exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline] syscall_return_slowpath arch/x86/entry/common.c:268 [inline] do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe The buggy address belongs to the object at ffff8801ce7f2500 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 16 bytes inside of 192-byte region [ffff8801ce7f2500, ffff8801ce7f25c0) The buggy address belongs to the page: page:ffffea000739fc80 count:1 mapcount:0 mapping:ffff8801da800040 index:0x0 flags: 0x2fffc0000000100(slab) raw: 02fffc0000000100 ffffea0006f6e548 ffffea000737b948 ffff8801da800040 raw: 0000000000000000 ffff8801ce7f2000 0000000100000010 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8801ce7f2400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8801ce7f2480: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc >ffff8801ce7f2500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8801ce7f2580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff8801ce7f2600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
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In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.