Date:   Mon, 28 Sep 2020 14:39:25 +0100
From:   Andrew Price <anprice@...hat.com>
To:     agruenba@...hat.com, rpeterso@...hat.com
Cc:     syzbot <syzbot+50a8a9cf8127f2c6f5df@...kaller.appspotmail.com>,
        cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [Cluster-devel] general protection fault in gfs2_withdraw

On 26/09/2020 18:21, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    7c7ec322 Merge tag 'for-linus' of git://git.kernel.org/pub..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f2ff27900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6184b75aa6d48d66
> dashboard link: https://syzkaller.appspot.com/bug?extid=50a8a9cf8127f2c6f5df
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=160fb773900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1104f109900000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+50a8a9cf8127f2c6f5df@...kaller.appspotmail.com
> 
> gfs2: fsid=syz:syz.0: fatal: invalid metadata block
>    bh = 2072 (magic number)
>    function = gfs2_meta_indirect_buffer, file = fs/gfs2/meta_io.c, line = 417
> gfs2: fsid=syz:syz.0: about to withdraw this file system
> general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]
> CPU: 0 PID: 6842 Comm: syz-executor264 Not tainted 5.9.0-rc6-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:signal_our_withdraw fs/gfs2/util.c:97 [inline]

Seems that it's withdrawing in the init_inodes() path early enough 
(while looking up the jindex) that sdp->sd_jdesc is still NULL here:

   static void signal_our_withdraw(struct gfs2_sbd *sdp)
   {
           struct gfs2_glock *gl = sdp->sd_live_gh.gh_gl;
           struct inode *inode = sdp->sd_jdesc->jd_inode;

I'm undecided as to whether the bug is that we're withdrawing that early 
at all, or that we're not checking for NULL there?

Probably introduced by:

601ef0d52e96 gfs2: Force withdraw to replay journals and wait for it to 
finish

Andy

> RIP: 0010:gfs2_withdraw+0x2b0/0xe20 fs/gfs2/util.c:294
> Code: e8 03 48 89 44 24 38 42 80 3c 38 00 74 08 48 89 ef e8 34 f7 69 fe 48 89 6c 24 20 48 8b 6d 00 48 83 c5 70 48 89 e8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 ef e8 11 f7 69 fe 48 8b 45 00 48 89 44
> RSP: 0018:ffffc900057474f0 EFLAGS: 00010202
> RAX: 000000000000000e RBX: ffff8880a71e0000 RCX: 98268db4dfe86a00
> RDX: ffff888092bb6100 RSI: 0000000000000000 RDI: ffff8880a71e0430
> RBP: 0000000000000070 R08: ffffffff834ad50c R09: ffffed1015d041c3
> R10: ffffed1015d041c3 R11: 0000000000000000 R12: 1ffff11014e3c04d
> R13: ffff8880a71e0050 R14: ffff8880a71e026c R15: dffffc0000000000
> FS:  000000000233b880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f74f826d6c0 CR3: 00000000a04cc000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   gfs2_meta_check_ii+0x70/0x80 fs/gfs2/util.c:450
>   gfs2_metatype_check_i fs/gfs2/util.h:126 [inline]
>   gfs2_meta_indirect_buffer+0x29f/0x380 fs/gfs2/meta_io.c:417
>   gfs2_meta_inode_buffer fs/gfs2/meta_io.h:70 [inline]
>   gfs2_inode_refresh+0x65/0xc00 fs/gfs2/glops.c:438
>   inode_go_lock+0x12c/0x480 fs/gfs2/glops.c:468
>   do_promote+0x4db/0xcd0 fs/gfs2/glock.c:390
>   finish_xmote+0x907/0x1350 fs/gfs2/glock.c:560
>   do_xmote+0xadb/0x14c0 fs/gfs2/glock.c:686
>   gfs2_glock_nq+0xac3/0x14d0 fs/gfs2/glock.c:1410
>   gfs2_glock_nq_init fs/gfs2/glock.h:238 [inline]
>   gfs2_lookupi+0x36f/0x4f0 fs/gfs2/inode.c:317
>   gfs2_lookup_simple+0xa4/0x100 fs/gfs2/inode.c:268
>   init_journal+0x132/0x1970 fs/gfs2/ops_fstype.c:620
>   init_inodes fs/gfs2/ops_fstype.c:756 [inline]
>   gfs2_fill_super+0x2717/0x3fe0 fs/gfs2/ops_fstype.c:1125
>   get_tree_bdev+0x3e9/0x5f0 fs/super.c:1342
>   gfs2_get_tree+0x4c/0x1f0 fs/gfs2/ops_fstype.c:1201
>   vfs_get_tree+0x88/0x270 fs/super.c:1547
>   do_new_mount fs/namespace.c:2875 [inline]
>   path_mount+0x179d/0x29e0 fs/namespace.c:3192
>   do_mount fs/namespace.c:3205 [inline]
>   __do_sys_mount fs/namespace.c:3413 [inline]
>   __se_sys_mount+0x126/0x180 fs/namespace.c:3390
>   do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x458e1a
> Code: b8 08 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 fd ad fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 da ad fb ff c3 66 0f 1f 84 00 00 00 00 00
> RSP: 002b:00007ffc76f65c88 EFLAGS: 00000293 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007ffc76f65ce0 RCX: 0000000000458e1a
> RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffc76f65ca0
> RBP: 00007ffc76f65ca0 R08: 00007ffc76f65ce0 R09: 00007ffc00000015
> R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000809
> R13: 0000000000000004 R14: 0000000000000003 R15: 0000000000000003
> Modules linked in:
> ---[ end trace 1e62174917573e95 ]---
> RIP: 0010:signal_our_withdraw fs/gfs2/util.c:97 [inline]
> RIP: 0010:gfs2_withdraw+0x2b0/0xe20 fs/gfs2/util.c:294
> Code: e8 03 48 89 44 24 38 42 80 3c 38 00 74 08 48 89 ef e8 34 f7 69 fe 48 89 6c 24 20 48 8b 6d 00 48 83 c5 70 48 89 e8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 ef e8 11 f7 69 fe 48 8b 45 00 48 89 44
> RSP: 0018:ffffc900057474f0 EFLAGS: 00010202
> RAX: 000000000000000e RBX: ffff8880a71e0000 RCX: 98268db4dfe86a00
> RDX: ffff888092bb6100 RSI: 0000000000000000 RDI: ffff8880a71e0430
> RBP: 0000000000000070 R08: ffffffff834ad50c R09: ffffed1015d041c3
> R10: ffffed1015d041c3 R11: 0000000000000000 R12: 1ffff11014e3c04d
> R13: ffff8880a71e0050 R14: ffff8880a71e026c R15: dffffc0000000000
> FS:  000000000233b880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f74f826d6c0 CR3: 00000000a04cc000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 

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