[Ocfs2-devel] [PATCH] ocfs2: fix a null pointer derefrence in ocfs2_block_group_clear_bits()

[Andrew Morton]

On Tue, 10 Mar 2020 21:07:06 +0800 lishan <lishan24 at huawei.com> wrote:

> On 2020/3/9 16:26, lishan wrote:
> > A NULL pointer panic dereference in ocfs2_block_group_clear_bits() happen again.
> > The information of NULL pointer stack as follows:
> > 
> > PID: 81866  TASK: ffffa07c3c21ae80  CPU: 66  COMMAND: "fallocate"
> >   #0 [ffff0000b4d6b0b0] machine_kexec at ffff0000800a2954
> >   #1 [ffff0000b4d6b110] __crash_kexec at ffff0000801bab34
> >   #2 [ffff0000b4d6b2a0] panic at ffff0000800f02cc
> >   #3 [ffff0000b4d6b380] die at ffff00008008f6ac
> >   #4 [ffff0000b4d6b3d0] bug_handler at ffff00008008f744
> >   #5 [ffff0000b4d6b400] brk_handler at ffff000080085d1c
> >   #6 [ffff0000b4d6b420] do_debug_exception at ffff000080081194
> >   #7 [ffff0000b4d6b630] el1_dbg at ffff00008008332c
> >       PC: ffff00000190e9c0  [_ocfs2_free_suballoc_bits+1608]
> >       LR: ffff00000190e990  [_ocfs2_free_suballoc_bits+1560]
> >       SP: ffff0000b4d6b640  PSTATE: 60400009
> >      X29: ffff0000b4d6b650  X28: 0000000000000000  X27: 00000000000052f3
> >      X26: ffff807c511a9570  X25: ffff807ca0054000  X24: 00000000000052f2
> >      X23: 0000000000000001  X22: ffff807c7cde7a90  X21: ffff0000811d9000
> >      X20: ffff807c5e7d2000  X19: ffff00000190c768  X18: 0000000000000000
> >      X17: 0000000000000000  X16: ffff000080a032f0  X15: 0000000000000000
> >      X14: ffffffffffffffff  X13: fffffffffffffff7  X12: ffffffffffffffff
> >      X11: 0000000000000038  X10: 0101010101010101   X9: ffffffffffffffff
> >       X8: 7f7f7f7f7f7f7f7f   X7: 0000000000000000   X6: 0000000000000080
> >       X5: 0000000000000000   X4: 0000000000000002   X3: ffff00000199f390
> >       X2: a603c08321456e00   X1: ffff807c7cde7a90   X0: 0000000000000000
> >   #8 [ffff0000b4d6b650] _ocfs2_free_suballoc_bits at ffff00000190e9bc [ocfs2]
> >   #9 [ffff0000b4d6b710] _ocfs2_free_clusters at ffff0000019110d4 [ocfs2]
> >  #10 [ffff0000b4d6b790] ocfs2_free_clusters at ffff000001913e94 [ocfs2]
> >  #11 [ffff0000b4d6b7d0] __ocfs2_flush_truncate_log at ffff0000018b5294 [ocfs2]
> >  #12 [ffff0000b4d6b8a0] ocfs2_remove_btree_range at ffff0000018bb34c [ocfs2]
> >  #13 [ffff0000b4d6b960] ocfs2_commit_truncate at ffff0000018bc76c [ocfs2]
> >  #14 [ffff0000b4d6ba60] ocfs2_wipe_inode at ffff0000018e57bc [ocfs2]
> >  #15 [ffff0000b4d6bb00] ocfs2_evict_inode at ffff0000018e5db8 [ocfs2]
> >  #16 [ffff0000b4d6bb70] evict at ffff000080365040
> >  #17 [ffff0000b4d6bba0] iput at ffff0000803655d8
> >  #18 [ffff0000b4d6bbe0] ocfs2_dentry_iput at ffff0000018c60a0 [ocfs2]
> >  #19 [ffff0000b4d6bc30] dentry_unlink_inode at ffff00008035ef58
> >  #20 [ffff0000b4d6bc50] __dentry_kill at ffff000080360384
> >  #21 [ffff0000b4d6bc80] dentry_kill at ffff000080360670
> >  #22 [ffff0000b4d6bcb0] dput at ffff00008036093c
> >  #23 [ffff0000b4d6bcf0] __fput at ffff000080343930
> >  #24 [ffff0000b4d6bd40] ____fput at ffff000080343aac
> >  #25 [ffff0000b4d6bd60] task_work_run at ffff0000801172fc
> > 
> > The direct panic reason is that bh2jh (group_bh)-> b_committed_data is null.
> > It is presumed that the network was disconnected during the write process,
> > causing the transaction abort. as follows:
> > jbd2_journal_abort
> >   .......
> >   jbd2_journal_commit_transaction
> >     jh->b_committed_data = NULL;
> > 
> > _ocfs2_free_suballoc_bits
> >   ocfs2_block_group_clear_bits
> >     // undo_bg is now set to null
> >     BUG_ON(!undo_bg);
> > 
> > When applying for free space, if b_committed_data is null,
> > it will be directly occupied, as follows:
> > ocfs2_cluster_group_search
> >   ocfs2_block_group_find_clear_bits
> >     ocfs2_test_bg_bit_allocatable:
> >       bg = (struct ocfs2_group_desc *) bh2jh(bg_bh)->b_committed_data;
> >       if (bg)
> >         ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
> >       else
> >         ret = 1;
> > b_committed_data is an intermediate state backup for bitmap transaction commits,
> > newly applied space can overwrite previous dirty data,
> > so, I think, while free clusters, if b_committed_data is null, ignore it.
> > Host panic directly, too violent.

(top-posting repaired)

> ping ?
> cc Andrew Morton

There's something dreadfully wrong with the ocfs2-devel mailing list. 
I almost never receive patches when people add me to cc.  I've never
seen much of a pattern to it - it just drops stuff everywhere.

Who is the admin for this list?  Can we please move it to kernel.org?

Regarding this patch, I did actually receive one email from the server.
>From Joseph:

: > +		if (!undo_bg)
: > +			mlog(ML_NOTICE, "%s: group descriptor # %llu (device %s) journal "
: > +					"b_committed_data had been cleared.\n",
: > +					OCFS2_SB(alloc_inode->i_sb)->uuid_str,
: > +					(unsigned long long)le64_to_cpu(bg->bg_blkno),
: > +					alloc_inode->i_sb->s_id);
: 
: Seems a kind of workaround.
: I am worrying about other abnormal cases of NULL b_committed_data, it
: may lead to a corrupt filesystem.
: So how about isolating the journal abort case?