KASAN: use-after-free Write in __alloc_skb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 69b94dd6 Linux 4.14.189
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1737ca90900000
kernel config: https://syzkaller.appspot.com/x/.config?x=80d63ff414fa81b0
dashboard link: https://syzkaller.appspot.com/bug?extid=4fcc32fe7c89dc09679d
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16256cdf100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=146a1130900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4fcc32...@syzkaller.appspotmail.com

batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (-224)
batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (-224)
batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (-224)
==================================================================
BUG: KASAN: use-after-free in memset include/linux/string.h:357 [inline]
BUG: KASAN: use-after-free in __alloc_skb+0x2e0/0x510 net/core/skbuff.c:234
Write of size 36 at addr ffff88819ff98300 by task swapper/0/0

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x283 lib/dump_stack.c:58
print_address_description.cold+0x54/0x1d3 mm/kasan/report.c:252
kasan_report_error.cold+0x8a/0x194 mm/kasan/report.c:351
kasan_report+0x6f/0x7b mm/kasan/report.c:409
memset+0x20/0x40 mm/kasan/kasan.c:285
memset include/linux/string.h:357 [inline]
__alloc_skb+0x2e0/0x510 net/core/skbuff.c:234
alloc_skb include/linux/skbuff.h:980 [inline]
alloc_skb_with_frags+0x85/0x500 net/core/skbuff.c:5228
sock_alloc_send_pskb+0x577/0x6d0 net/core/sock.c:2083
mld_newpack+0x1cb/0x720 net/ipv6/mcast.c:1585
add_grhead+0x265/0x330 net/ipv6/mcast.c:1691
add_grec+0xc40/0xed0 net/ipv6/mcast.c:1822
mld_send_cr net/ipv6/mcast.c:1948 [inline]
mld_ifc_timer_expire+0x508/0xcd0 net/ipv6/mcast.c:2455
call_timer_fn+0x14a/0x650 kernel/time/timer.c:1279
expire_timers+0x232/0x4d0 kernel/time/timer.c:1318
__run_timers kernel/time/timer.c:1636 [inline]
run_timer_softirq+0x1d5/0x5a0 kernel/time/timer.c:1649
__do_softirq+0x254/0xa1d kernel/softirq.c:288
invoke_softirq kernel/softirq.c:368 [inline]
irq_exit+0x193/0x240 kernel/softirq.c:409
exiting_irq arch/x86/include/asm/apic.h:648 [inline]
smp_apic_timer_interrupt+0x141/0x5e0 arch/x86/kernel/apic/apic.c:1102
apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:793
</IRQ>
RIP: 0010:native_safe_halt+0xe/0x10 arch/x86/include/asm/irqflags.h:61
RSP: 0018:ffffffff87c07e78 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff10
RAX: 1ffffffff0fa2d24 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff87c76b44
RBP: ffffffff87d16910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: fffffbfff0f8ec58
R13: ffffffff87c762c0 R14: 0000000000000000 R15: 0000000000000000
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0x47/0x370 arch/x86/kernel/process.c:558
cpuidle_idle_call kernel/sched/idle.c:156 [inline]
do_idle+0x250/0x3c0 kernel/sched/idle.c:246
cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:351
start_kernel+0x750/0x770 init/main.c:708
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:240

The buggy address belongs to the page:
page:ffffea00067fe600 count:0 mapcount:0 mapping: (null) index:0x0
flags: 0x57ffe0000000000()
raw: 057ffe0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: ffffea00067fe620 ffffea00067fe620 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88819ff98200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88819ff98280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88819ff98300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88819ff98380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88819ff98400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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