On Wed, 2023-05-24 at 17:57 -0400, Paul Moore wrote: > On Wed, May 24, 2023 at 11:50 AM Roberto Sassu > <roberto.sassu@xxxxxxxxxxxxxxx> wrote: > > On Wed, 2023-05-24 at 11:11 -0400, Paul Moore wrote: > > > On Wed, May 24, 2023 at 5:59 AM syzbot > > > <syzbot+0a684c061589dcc30e51@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > syzbot has bisected this issue to: > > > > > > > > commit d82dcd9e21b77d338dc4875f3d4111f0db314a7c > > > > Author: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > 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 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 <reiserfs_get_block>, iomap=iomap@entry=0x0 <fixed_percpu_data>) 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 <reiserfs_get_block>) at ./arch/x86/include/asm/jump_label.h:27 #4 0xffffffff821a3e3d in reiserfs_write_begin (file=<optimized out>, mapping=<optimized out>, pos=61440, len=1, pagep=<optimized out>, fsdata=<optimized out>) 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=<optimized out>, flags=0, pos_l=61440, vlen=1, vec=0x20000480, fd=5) at fs/read_write.c:1089 #15 __se_sys_pwritev2 (pos_h=<optimized out>, 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=<optimized out>, regs=0xffffc9002130ff58) at arch/x86/entry/common.c:50 #18 do_syscall_64 (regs=0xffffc9002130ff58, nr=<optimized out>) 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
