WARNING: refcount bug in uprobe_mmap

[syzbot <syzbot+e61dd1b2a6fb2ffd2dee@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    fd821bf0 Add linux-next specific files for 20210201
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17255354d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=80ac9f64e6e2c06
dashboard link: https://syzkaller.appspot.com/bug?extid=e61dd1b2a6fb2ffd2dee

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e61dd1b2a6fb2ffd2dee@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 0 PID: 10416 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Modules linked in:
CPU: 0 PID: 10416 Comm: syz-executor.5 Not tainted 5.11.0-rc6-next-20210201-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 09 31 ff 89 de e8 87 b5 b0 fd 84 db 0f 85 36 ff ff ff e8 fa ae b0 fd 48 c7 c7 60 f7 be 89 c6 05 4a a8 4e 09 01 e8 be 96 fd 04 <0f> 0b e9 17 ff ff ff e8 db ae b0 fd 0f b6 1d 2f a8 4e 09 31 ff 89
RSP: 0018:ffffc9000262fb80 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff815b3b35 RDI: fffff520004c5f62
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815acd0e R11: 0000000000000000 R12: ffff888011d9d800
R13: ffffc9000262fc10 R14: ffffc9000262fc10 R15: ffff888011d9d818
FS:  00007f3dcdee1700(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32d27000 CR3: 00000000291a8000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __refcount_add include/linux/refcount.h:199 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 get_uprobe kernel/events/uprobes.c:597 [inline]
 build_probe_list kernel/events/uprobes.c:1312 [inline]
 uprobe_mmap+0x8ff/0x1080 kernel/events/uprobes.c:1382
 mmap_region+0x56c/0x1730 mm/mmap.c:1881
 do_mmap+0xcff/0x11d0 mm/mmap.c:1580
 vm_mmap_pgoff+0x1b7/0x290 mm/util.c:519
 ksys_mmap_pgoff+0x49c/0x620 mm/mmap.c:1631
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x465b09
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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3dcdee1188 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000465b09
RDX: 0000000000000000 RSI: 0000000000003000 RDI: 0000000020007000
RBP: 00000000004b069f R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000000412 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007ffcf33596cf R14: 00007f3dcdee1300 R15: 0000000000022000


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