From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roberto Sassu Subject: Re: [syzbot] [reiserfs?] INFO: task hung in flush_old_commits Date: Tue, 30 May 2023 17:44:25 +0200 Message-ID: <8658676c-4b14-99d9-2aa5-7c6525617822@huaweicloud.com> References: <000000000000be039005fc540ed7@google.com> <00000000000018faf905fc6d9056@google.com> <813148798c14a49cbdf0f500fbbbab154929e6ed.camel@huaweicloud.com> <58cebdd9318bd4435df6c0cf45318abd3db0fff8.camel@huaweicloud.com> <20230530112147.spvyjl7b4ss7re47@quack3> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Content-Language: en-US In-Reply-To: <20230530112147.spvyjl7b4ss7re47@quack3> List-ID: Content-Type: text/plain; charset="utf-8"; format="flowed" To: Jan Kara Cc: Paul Moore , linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, reiserfs-devel@vger.kernel.org, roberto.sassu@huawei.com, syzkaller-bugs@googlegroups.com, syzbot , Jeff Mahoney On 5/30/2023 1:21 PM, Jan Kara wrote: > On Fri 26-05-23 11:45:57, Roberto Sassu wrote: >> On Wed, 2023-05-24 at 17:57 -0400, Paul Moore wrote: >>> On Wed, May 24, 2023 at 11:50 AM Roberto Sassu >>> wrote: >>>> On Wed, 2023-05-24 at 11:11 -0400, Paul Moore wrote: >>>>> On Wed, May 24, 2023 at 5:59 AM syzbot >>>>> wrote: >>>>>> syzbot has bisected this issue to: >>>>>> >>>>>> commit d82dcd9e21b77d338dc4875f3d4111f0db314a7c >>>>>> Author: Roberto Sassu >>>>>> Date: Fri Mar 31 12:32:18 2023 +0000 >>>>>> >>>>>> reiserfs: Add security prefix to xattr name in reiserfs_security_write() >>>>>> >>>>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11c39639280000 >>>>>> start commit: 421ca22e3138 Merge tag 'nfs-for-6.4-2' of git://git.linux-.. >>>>>> git tree: upstream >>>>>> final oops: https://syzkaller.appspot.com/x/report.txt?x=13c39639280000 >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15c39639280000 >>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=7d8067683055e3f5 >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=0a684c061589dcc30e51 >>>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14312791280000 >>>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12da8605280000 >>>>>> >>>>>> Reported-by: syzbot+0a684c061589dcc30e51@syzkaller.appspotmail.com >>>>>> Fixes: d82dcd9e21b7 ("reiserfs: Add security prefix to xattr name in reiserfs_security_write()") >>>>>> >>>>>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection >>>>> >>>>> Roberto, I think we need to resolve this somehow. As I mentioned >>>>> earlier, I don't believe this to be a fault in your patch, rather that >>>>> patch simply triggered a situation that had not been present before, >>>>> likely because the reiserfs code always failed when writing LSM >>>>> xattrs. Regardless, we still need to fix the deadlocks that sysbot >>>>> has been reporting. >>>> >>>> Hi Paul >>>> >>>> ok, I will try. >>> >>> Thanks Roberto. If it gets to be too challenging, let us know and we >>> can look into safely disabling the LSM xattrs for reiserfs, I'll be >>> shocked if anyone is successfully using LSM xattrs on reiserfs. >> >> Ok, at least I know what happens... >> >> + Jan, Jeff >> >> I'm focusing on this reproducer, which works 100% of the times: >> >> https://syzkaller.appspot.com/text?tag=ReproSyz&x=163079f9280000 > > Well, the commit d82dcd9e21b ("reiserfs: Add security prefix to xattr name > in reiserfs_security_write()") looks obviously broken to me. It does: > > char xattr_name[XATTR_NAME_MAX + 1] = XATTR_SECURITY_PREFIX; > > Which is not how we can initialize strings in C... ;) Thanks for having a look! Sorry for the silly question, do I need to patch it? It is already in stable kernels... (next time I document myself better) Thanks Roberto >> This is the last lock, before things go wrong: >> >> Thread 5 hit Breakpoint 2, reiserfs_write_lock (s=s@entry=0xffff888066e28000) at fs/reiserfs/lock.c:24 >> 24 { >> (gdb) bt >> #0 reiserfs_write_lock (s=s@entry=0xffff888066e28000) at fs/reiserfs/lock.c:24 >> #1 0xffffffff821a559a in reiserfs_get_block (inode=inode@entry=0xffff888069fd0190, block=block@entry=15, bh_result=bh_result@entry=0xffff888075940000, create=create@entry=1) at fs/reiserfs/inode.c:680 >> #2 0xffffffff81f50254 in __block_write_begin_int (folio=0xffffea00019a9180, pos=pos@entry=61440, len=len@entry=1, get_block=get_block@entry=0xffffffff821a5390 , iomap=iomap@entry=0x0 ) at fs/buffer.c:2064 >> #3 0xffffffff81f5165a in __block_write_begin (page=page@entry=0xffffea00019a9180, pos=pos@entry=61440, len=len@entry=1, get_block=get_block@entry=0xffffffff821a5390 ) at ./arch/x86/include/asm/jump_label.h:27 >> #4 0xffffffff821a3e3d in reiserfs_write_begin (file=, mapping=, pos=61440, len=1, pagep=, fsdata=) at fs/reiserfs/inode.c:2779 >> #5 0xffffffff81aec252 in generic_perform_write (iocb=iocb@entry=0xffffc9002130fb60, i=i@entry=0xffffc9002130fd00) at mm/filemap.c:3923 >> #6 0xffffffff81b0604e in __generic_file_write_iter (iocb=iocb@entry=0xffffc9002130fb60, from=from@entry=0xffffc9002130fd00) at mm/filemap.c:4051 >> #7 0xffffffff81b06383 in generic_file_write_iter (iocb=0xffffc9002130fb60, from=0xffffc9002130fd00) at mm/filemap.c:4083 >> #8 0xffffffff81e3240b in call_write_iter (file=0xffff888012692d00, iter=0xffffc9002130fd00, kio=0xffffc9002130fb60) at ./include/linux/fs.h:1868 >> #9 do_iter_readv_writev (filp=filp@entry=0xffff888012692d00, iter=iter@entry=0xffffc9002130fd00, ppos=ppos@entry=0xffffc9002130fe90, type=type@entry=1, flags=flags@entry=0) at fs/read_write.c:735 >> #10 0xffffffff81e33da4 in do_iter_write (flags=0, pos=0xffffc9002130fe90, iter=0xffffc9002130fd00, file=0xffff888012692d00) at fs/read_write.c:860 >> #11 do_iter_write (file=0xffff888012692d00, iter=0xffffc9002130fd00, pos=0xffffc9002130fe90, flags=0) at fs/read_write.c:841 >> #12 0xffffffff81e34611 in vfs_writev (file=file@entry=0xffff888012692d00, vec=vec@entry=0x20000480, vlen=vlen@entry=1, pos=pos@entry=0xffffc9002130fe90, flags=flags@entry=0) at fs/read_write.c:933 >> #13 0xffffffff81e34fd6 in do_pwritev (fd=fd@entry=5, vec=vec@entry=0x20000480, vlen=vlen@entry=1, pos=pos@entry=61440, flags=flags@entry=0) at fs/read_write.c:1030 >> #14 0xffffffff81e3b61f in __do_sys_pwritev2 (pos_h=, flags=0, pos_l=61440, vlen=1, vec=0x20000480, fd=5) at fs/read_write.c:1089 >> #15 __se_sys_pwritev2 (pos_h=, flags=0, pos_l=61440, vlen=1, vec=536872064, fd=5) at fs/read_write.c:1080 >> #16 __x64_sys_pwritev2 (regs=0xffffc9002130ff58) at fs/read_write.c:1080 >> #17 0xffffffff880dd279 in do_syscall_x64 (nr=, regs=0xffffc9002130ff58) at arch/x86/entry/common.c:50 >> #18 do_syscall_64 (regs=0xffffc9002130ff58, nr=) at arch/x86/entry/common.c:80 >> #19 0xffffffff8820008b in entry_SYSCALL_64 () at arch/x86/entry/entry_64.S:120 >> #20 0x0000000000406e00 in ?? () >> #21 0x00007f99e21b5000 in ?? () >> #22 0x0000000000000000 in ?? () >> >> After that, there is a very long loop doing: >> >> Thread 5 hit Breakpoint 3, reiserfs_read_bitmap_block (sb=sb@entry=0xffff888066e28000, bitmap=bitmap@entry=1) at fs/reiserfs/bitmap.c:1417 >> 1417 { >> (gdb) c >> Continuing. >> >> Thread 5 hit Breakpoint 3, reiserfs_read_bitmap_block (sb=sb@entry=0xffff888066e28000, bitmap=bitmap@entry=2) at fs/reiserfs/bitmap.c:1417 >> 1417 { >> (gdb) >> Continuing. >> >> and so on... >> >> [ 628.589974][ T6003] REISERFS warning (device loop0): sh-2029: %s: bitmap block (#%u) reading failed reiserfs_read_bitmap_block: reiserfs_read_bitmap_block >> >> This message appears because we are here: >> >> struct buffer_head *reiserfs_read_bitmap_block(struct super_block *sb, >> unsigned int bitmap) >> { >> >> [...] >> >> bh = sb_bread(sb, block); >> if (bh == NULL) >> reiserfs_warning(sb, "sh-2029: %s: bitmap block (#%u) " >> "reading failed", __func__, block); >> >> The hanging task (kthread) is trying to hold the same lock, which >> unfortunately is not going to be released soon: >> >> static int reiserfs_sync_fs(struct super_block *s, int wait) >> { >> >> [...] >> >> reiserfs_write_lock(s); >> >> I didn't get yet if the reason of this long loop is because we cannot >> flush at this point, or just because of the test. I tried to >> synchronously flush, but didn't make any difference. >> >> I did a very simple change, which can be totally wrong: >> >> @@ -94,7 +96,7 @@ static void flush_old_commits(struct work_struct *work) >> * trylock as reiserfs_cancel_old_flush() may be waiting for this work >> * to complete with s_umount held. >> */ >> - if (!down_read_trylock(&s->s_umount)) { >> + if (sbi->lock_owner || !down_read_trylock(&s->s_umount)) { >> /* Requeue work if we are not cancelling it */ >> spin_lock(&sbi->old_work_lock); >> if (sbi->work_queued == 1) >> >> >> If the lock is held, instead of waiting, reschedule the flush. >> >> Anyway, at least this report does not seem to be related to fixing >> security xattrs. >> >> Roberto >>