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SubjectKASAN: use-after-free Read in get_block
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Hello,

syzbot found the following crash on:

HEAD commit: 189522da Merge tag 'for_linus' of git://git.kernel.org/pub..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14193487e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=b7a70e992f2f9b68
dashboard link: https://syzkaller.appspot.com/bug?extid=3b7b03a0c28948054fb5
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16cb136fe00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12fd5930100000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=122603f0100000
final crash: https://syzkaller.appspot.com/x/report.txt?x=112603f0100000
console output: https://syzkaller.appspot.com/x/log.txt?x=162603f0100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+3b7b03a0c28948054fb5@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in add_chain fs/minix/itree_common.c:14 [inline]
BUG: KASAN: use-after-free in get_branch fs/minix/itree_common.c:52 [inline]
BUG: KASAN: use-after-free in get_block+0x110f/0x1380 fs/minix/itree_common.c:160
Read of size 2 at addr ffff888082c493be by task syz-executor205/7041

CPU: 1 PID: 7041 Comm: syz-executor205 Not tainted 5.7.0-rc2-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+0x188/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:382
__kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
kasan_report+0x33/0x50 mm/kasan/common.c:625
add_chain fs/minix/itree_common.c:14 [inline]
get_branch fs/minix/itree_common.c:52 [inline]
get_block+0x110f/0x1380 fs/minix/itree_common.c:160
minix_get_block+0xe5/0x110 fs/minix/inode.c:376
block_read_full_page+0x2bf/0x1010 fs/buffer.c:2290
do_read_cache_page+0x1053/0x1810 mm/filemap.c:2768
read_mapping_page include/linux/pagemap.h:397 [inline]
dir_get_page.isra.0+0x1d/0x60 fs/minix/dir.c:70
minix_find_entry+0x200/0x7b0 fs/minix/dir.c:170
minix_inode_by_name+0x6d/0x452 fs/minix/dir.c:454
minix_lookup fs/minix/namei.c:30 [inline]
minix_lookup+0x103/0x190 fs/minix/namei.c:22
lookup_open+0x8d7/0x1320 fs/namei.c:3060
open_last_lookups fs/namei.c:3155 [inline]
path_openat+0x93f/0x27d0 fs/namei.c:3343
do_filp_open+0x192/0x260 fs/namei.c:3373
do_sys_openat2+0x585/0x7d0 fs/open.c:1148
do_sys_open+0xc3/0x140 fs/open.c:1164
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x445ef9
Code: ed cb fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 bb cb fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc4f7dec58 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000445ef9
RDX: 0000000000000000 RSI: 0000000000020040 RDI: 0000000020000040
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000402fd0
R10: 00007ffc4f7deb30 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000402fd0 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:ffffea00020b1240 refcount:2 mapcount:0 mapping:000000007b3de2b2 index:0x2f24f
minix_aops name:"/"
flags: 0xfffe0000002016(referenced|uptodate|lru|private)
raw: 00fffe0000002016 ffffea0002389288 ffffea00020b1388 ffff8880846492e8
raw: 000000000002f24f ffff8880856d0ae0 00000002ffffffff ffff8880a9550000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8880a9550000

Memory state around the buggy address:
ffff888082c49280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888082c49300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888082c49380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
^
ffff888082c49400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888082c49480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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