bisecting fixing commit since 7d120bf21c05cbe30a679f0feeca884eeaceb069
building syzkaller on 79b211f74b08737aeb4934c6ff69a263b3c38013
testing commit 7d120bf21c05cbe30a679f0feeca884eeaceb069 with gcc (GCC) 8.1.0
kernel signature: 90fb8f133aaded5d93a00fbf09752b9b9a5792444a3166d917a990b06d19c8e0
all runs: crashed: KASAN: use-after-free Read in eth_type_trans
testing current HEAD 93556fb211fa7f1e18f869bdce0c225c25594942
testing commit 93556fb211fa7f1e18f869bdce0c225c25594942 with gcc (GCC) 8.1.0
kernel signature: 22e140aea9ab04d8dc2863e559c8237dc883bde5cfe260a1c85cbfd685851246
run #0: crashed: KASAN: use-after-free Read in eth_type_trans
run #1: crashed: KASAN: use-after-free Read in eth_type_trans
run #2: crashed: KASAN: use-after-free Read in eth_type_trans
run #3: crashed: KASAN: out-of-bounds Read in eth_type_trans
run #4: crashed: KASAN: use-after-free Read in eth_type_trans
run #5: crashed: KASAN: use-after-free Read in eth_type_trans
run #6: crashed: KASAN: use-after-free Read in eth_type_trans
run #7: crashed: KASAN: use-after-free Read in eth_type_trans
run #8: crashed: KASAN: slab-out-of-bounds Read in eth_type_trans
run #9: crashed: KASAN: use-after-free Read in eth_type_trans
revisions tested: 2, total time: 26m14.867974154s (build: 18m37.036558526s, test: 6m18.928591603s)
the crash still happens on HEAD
commit msg: Linux 4.19.111
crash: KASAN: use-after-free Read in eth_type_trans
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): vxcan0: link becomes ready
==================================================================
BUG: KASAN: use-after-free in is_multicast_ether_addr_64bits include/linux/etherdevice.h:139 [inline]
BUG: KASAN: use-after-free in eth_type_trans+0x5c1/0x6e0 net/ethernet/eth.c:168
Read of size 8 at addr ffff888086ff0040 by task syz-executor.0/7229

CPU: 1 PID: 7229 Comm: syz-executor.0 Not tainted 4.19.111-syzkaller #0
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+0x123/0x177 lib/dump_stack.c:118
 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
 is_multicast_ether_addr_64bits include/linux/etherdevice.h:139 [inline]
 eth_type_trans+0x5c1/0x6e0 net/ethernet/eth.c:168
 napi_frags_finish net/core/dev.c:5675 [inline]
 napi_gro_frags+0x546/0x8e0 net/core/dev.c:5749
 tun_get_user+0x25ec/0x47d0 drivers/net/tun.c:1943
 tun_chr_write_iter+0xaf/0x150 drivers/net/tun.c:1989
 call_write_iter include/linux/fs.h:1820 [inline]
 do_iter_readv_writev+0x4ae/0x960 fs/read_write.c:681
 do_iter_write+0x12a/0x510 fs/read_write.c:960
 vfs_writev+0x16f/0x2d0 fs/read_write.c:1005
 do_writev+0x110/0x330 fs/read_write.c:1040
 __do_sys_writev fs/read_write.c:1113 [inline]
 __se_sys_writev fs/read_write.c:1110 [inline]
 __x64_sys_writev+0x70/0xb0 fs/read_write.c:1110
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a7d1
Code: 75 14 b8 14 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 e4 b7 fb ff c3 48 83 ec 08 e8 fa 2c 00 00 48 89 04 24 b8 14 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 43 2d 00 00 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007fb19bc63ba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 0000000000207843 RCX: 000000000045a7d1
RDX: 0000000000000001 RSI: 00007fb19bc63c00 RDI: 00000000000000f0
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000293 R12: 00007fb19bc646d4
R13: 00000000004cab1f R14: 00000000004e4040 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea00021bfc00 count:0 mapcount:0 mapping:0000000000000000 index:0x1
flags: 0xfffe0000000000()
raw: 00fffe0000000000 dead000000000100 dead000000000200 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888086feff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888086feff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888086ff0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                           ^
 ffff888086ff0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888086ff0100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================