KASAN: use-after-free Read in batadv_interface_tx

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    903b77c63167 Merge tag 'linux-kselftest-4.21-rc1' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=168acbdd400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=53a2f2aa0b1f7606
dashboard link: https://syzkaller.appspot.com/bug?extid=7d20bc3f1ddddc0f9079
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11aa3b57400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12c907ed400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7d20bc3f1ddddc0f9079@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready
8021q: adding VLAN 0 to HW filter on device batadv0
==================================================================
BUG: KASAN: use-after-free in batadv_interface_tx+0x160a/0x18b0  
net/batman-adv/soft-interface.c:226
Read of size 2 at addr ffff88809f96aa4b by task syz-executor871/8379

CPU: 1 PID: 8379 Comm: syz-executor871 Not tainted 4.20.0+ #395
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+0x1d3/0x2c6 lib/dump_stack.c:113
 print_address_description.cold.5+0x9/0x1ff mm/kasan/report.c:187
 kasan_report.cold.6+0x1b/0x39 mm/kasan/report.c:317
 __asan_report_load_n_noabort+0xf/0x20 mm/kasan/generic_report.c:145
 batadv_interface_tx+0x160a/0x18b0 net/batman-adv/soft-interface.c:226
 __netdev_start_xmit include/linux/netdevice.h:4382 [inline]
 netdev_start_xmit include/linux/netdevice.h:4391 [inline]
 dev_direct_xmit+0x36c/0x6a0 net/core/dev.c:3930
 packet_direct_xmit+0xfb/0x170 net/packet/af_packet.c:246
 packet_snd net/packet/af_packet.c:2932 [inline]
 packet_sendmsg+0x298a/0x6ad0 net/packet/af_packet.c:2957
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 __sys_sendto+0x3d7/0x670 net/socket.c:1788
 __do_sys_sendto net/socket.c:1800 [inline]
 __se_sys_sendto net/socket.c:1796 [inline]
 __x64_sys_sendto+0xe1/0x1a0 net/socket.c:1796
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441eb9
Code: e8 4c ad 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 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 0f 83 fb 04 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffee312ce58 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441eb9
RDX: 000000000000000e RSI: 0000000020000180 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
R13: 00000000004028d0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 8368:
 save_stack+0x43/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 kasan_kmalloc+0xcb/0xd0 mm/kasan/common.c:482
 kasan_slab_alloc+0x12/0x20 mm/kasan/common.c:397
 kmem_cache_alloc+0x130/0x730 mm/slab.c:3541
 getname_flags+0xd0/0x590 fs/namei.c:140
 user_path_at_empty+0x2d/0x50 fs/namei.c:2608
 user_path_at include/linux/namei.h:57 [inline]
 do_faccessat+0x254/0x800 fs/open.c:378
 __do_sys_access fs/open.c:430 [inline]
 __se_sys_access fs/open.c:428 [inline]
 __x64_sys_access+0x59/0x80 fs/open.c:428
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8368:
 save_stack+0x43/0xd0 mm/kasan/common.c:73
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x83/0x290 mm/slab.c:3747
 putname+0xf2/0x130 fs/namei.c:261
 filename_lookup+0x39a/0x520 fs/namei.c:2357
 user_path_at_empty+0x40/0x50 fs/namei.c:2608
 user_path_at include/linux/namei.h:57 [inline]
 do_faccessat+0x254/0x800 fs/open.c:378
 __do_sys_access fs/open.c:430 [inline]
 __se_sys_access fs/open.c:428 [inline]
 __x64_sys_access+0x59/0x80 fs/open.c:428
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809f96a2c0
 which belongs to the cache names_cache of size 4096
The buggy address is located 1931 bytes inside of
 4096-byte region [ffff88809f96a2c0, ffff88809f96b2c0)
The buggy address belongs to the page:
page:ffffea00027e5a80 count:1 mapcount:0 mapping:ffff88821bc49080 index:0x0  
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002810f08 ffffea00027d0388 ffff88821bc49080
raw: 0000000000000000 ffff88809f96a2c0 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809f96a900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809f96a980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88809f96aa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff88809f96aa80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809f96ab00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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