KASAN: null-ptr-deref Read in filp_close

KASAN: null-ptr-deref Read in filp_close

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    5e60366d Merge tag 'fallthrough-fixes-clang-5.11-rc1' of g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f15413500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db720fe37a6a41d8
dashboard link: https://syzkaller.appspot.com/bug?extid=96cfd2b22b3213646a93
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e1a00b500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1128e41f500000

The issue was bisected to:

commit 582f1fb6b721facf04848d2ca57f34468da1813e
Author: Giuseppe Scrivano <gscrivan@redhat.com>
Date:   Wed Nov 18 10:47:45 2020 +0000

    fs, close_range: add flag CLOSE_RANGE_CLOEXEC

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16e85613500000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=15e85613500000
console output: https://syzkaller.appspot.com/x/log.txt?x=11e85613500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+96cfd2b22b3213646a93@syzkaller.appspotmail.com
Fixes: 582f1fb6b721 ("fs, close_range: add flag CLOSE_RANGE_CLOEXEC")

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline]
BUG: KASAN: null-ptr-deref in atomic64_read include/asm-generic/atomic-instrumented.h:837 [inline]
BUG: KASAN: null-ptr-deref in atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
BUG: KASAN: null-ptr-deref in filp_close+0x22/0x170 fs/open.c:1274
Read of size 8 at addr 0000000000000077 by task syz-executor511/8522

CPU: 1 PID: 8522 Comm: syz-executor511 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 __kasan_report mm/kasan/report.c:549 [inline]
 kasan_report.cold+0x5/0x37 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:186 [inline]
 check_memory_region+0x13d/0x180 mm/kasan/generic.c:192
 instrument_atomic_read include/linux/instrumented.h:71 [inline]
 atomic64_read include/asm-generic/atomic-instrumented.h:837 [inline]
 atomic_long_read include/asm-generic/atomic-long.h:29 [inline]
 filp_close+0x22/0x170 fs/open.c:1274
 close_files fs/file.c:402 [inline]
 put_files_struct fs/file.c:417 [inline]
 put_files_struct+0x1cc/0x350 fs/file.c:414
 exit_files+0x12a/0x170 fs/file.c:435
 do_exit+0xb4f/0x2a00 kernel/exit.c:818
 do_group_exit+0x125/0x310 kernel/exit.c:920
 get_signal+0x428/0x2100 kernel/signal.c:2792
 arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:811
 handle_signal_work kernel/entry/common.c:147 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
 exit_to_user_mode_prepare+0x124/0x200 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x447039
Code: Unable to access opcode bytes at RIP 0x44700f.
RSP: 002b:00007f1b1225cdb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000001 RBX: 00000000006dbc28 RCX: 0000000000447039
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00000000006dbc2c
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 00007fff223b6bef R14: 00007f1b1225d9c0 R15: 00000000006dbc2c
==================================================================


---
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Re: KASAN: null-ptr-deref Read in filp_close

[Christian Brauner]

On Thu, Dec 17, 2020 at 07:54:09AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    5e60366d Merge tag 'fallthrough-fixes-clang-5.11-rc1' of g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15f15413500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=db720fe37a6a41d8
> dashboard link: https://syzkaller.appspot.com/bug?extid=96cfd2b22b3213646a93
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e1a00b500000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1128e41f500000
> 
> The issue was bisected to:
> 
> commit 582f1fb6b721facf04848d2ca57f34468da1813e
> Author: Giuseppe Scrivano <gscrivan@redhat.com>
> Date:   Wed Nov 18 10:47:45 2020 +0000
> 
>     fs, close_range: add flag CLOSE_RANGE_CLOEXEC
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16e85613500000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15e85613500000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11e85613500000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+96cfd2b22b3213646a93@syzkaller.appspotmail.com
> Fixes: 582f1fb6b721 ("fs, close_range: add flag CLOSE_RANGE_CLOEXEC")

Ok, I think the bug is simply that max_fd is not correctly updated when
CLOSE_RANGE_UNSHARE is combined with CLOSE_RANGE_CLOEXEC.
I'll write a patch for syszbot to chew on.

Christian