Re: [PATCH -next v2] jbd2: Fix null-ptr-deref when process reserved list in jbd2_journal_commit_transaction

[Jan Kara]

On Wed 27-04-22 11:23:22, yebin wrote:
> Friendly ping...

Ted probably forgot to send his standard email but your patch is already in
with a slightly edited message: 23e3d7f7061f86 ("jbd2: fix a potential race
while discarding reserved buffers after an abort")

								Honza

> 
> On 2022/3/17 22:21, Ye Bin wrote:
> > we got issue as follows:
> > [   72.796117] EXT4-fs error (device sda): ext4_journal_check_start:83: comm fallocate: Detected aborted journal
> > [   72.826847] EXT4-fs (sda): Remounting filesystem read-only
> > fallocate: fallocate failed: Read-only file system
> > [   74.791830] jbd2_journal_commit_transaction: jh=0xffff9cfefe725d90 bh=0x0000000000000000 end delay
> > [   74.793597] ------------[ cut here ]------------
> > [   74.794203] kernel BUG at fs/jbd2/transaction.c:2063!
> > [   74.794886] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> > [   74.795533] CPU: 4 PID: 2260 Comm: jbd2/sda-8 Not tainted 5.17.0-rc8-next-20220315-dirty #150
> > [   74.798327] RIP: 0010:__jbd2_journal_unfile_buffer+0x3e/0x60
> > [   74.801971] RSP: 0018:ffffa828c24a3cb8 EFLAGS: 00010202
> > [   74.802694] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> > [   74.803601] RDX: 0000000000000001 RSI: ffff9cfefe725d90 RDI: ffff9cfefe725d90
> > [   74.804554] RBP: ffff9cfefe725d90 R08: 0000000000000000 R09: ffffa828c24a3b20
> > [   74.805471] R10: 0000000000000001 R11: 0000000000000001 R12: ffff9cfefe725d90
> > [   74.806385] R13: ffff9cfefe725d98 R14: 0000000000000000 R15: ffff9cfe833a4d00
> > [   74.807301] FS:  0000000000000000(0000) GS:ffff9d01afb00000(0000) knlGS:0000000000000000
> > [   74.808338] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [   74.809084] CR2: 00007f2b81bf4000 CR3: 0000000100056000 CR4: 00000000000006e0
> > [   74.810047] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [   74.810981] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [   74.811897] Call Trace:
> > [   74.812241]  <TASK>
> > [   74.812566]  __jbd2_journal_refile_buffer+0x12f/0x180
> > [   74.813246]  jbd2_journal_refile_buffer+0x4c/0xa0
> > [   74.813869]  jbd2_journal_commit_transaction.cold+0xa1/0x148
> > [   74.817550]  kjournald2+0xf8/0x3e0
> > [   74.819056]  kthread+0x153/0x1c0
> > [   74.819963]  ret_from_fork+0x22/0x30
> > 
> > Above issue may happen as follows:
> >          write                   truncate                   kjournald2
> > generic_perform_write
> >   ext4_write_begin
> >    ext4_walk_page_buffers
> >     do_journal_get_write_access ->add BJ_Reserved list
> >   ext4_journalled_write_end
> >    ext4_walk_page_buffers
> >     write_end_fn
> >      ext4_handle_dirty_metadata
> >                  ***************JBD2 ABORT**************
> >       jbd2_journal_dirty_metadata
> >   -> return -EROFS, jh in reserved_list
> >                                                     jbd2_journal_commit_transaction
> >                                                      while (commit_transaction->t_reserved_list)
> >                                                        jh = commit_transaction->t_reserved_list;
> >                          truncate_pagecache_range
> >                           do_invalidatepage
> > 			  ext4_journalled_invalidatepage
> > 			   jbd2_journal_invalidatepage
> > 			    journal_unmap_buffer
> > 			     __dispose_buffer
> > 			      __jbd2_journal_unfile_buffer
> > 			       jbd2_journal_put_journal_head ->put last ref_count
> > 			        __journal_remove_journal_head
> > 				 bh->b_private = NULL;
> > 				 jh->b_bh = NULL;
> > 				                      jbd2_journal_refile_buffer(journal, jh);
> > 							bh = jh2bh(jh);
> > 							->bh is NULL, later will trigger null-ptr-deref
> > 				 journal_free_journal_head(jh);
> > 
> > As after 96f1e0974575 commit, handle reserved list will not hold "journal->j_state_lock"
> > when kjournald2 commit transaction. So journal_unmap_buffer maybe free
> > journal_head when handle reserved list. And lead to null-ptr-deref or some
> > strange errors.
> > As reserved list almost time is empty. Use "journal->j_state_lock" to protect
> > handle reserved list can simply solve above issue.
> > 
> > Fixes: 96f1e0974575("jbd2: avoid long hold times of j_state_lock while committing a transaction")
> > Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> > ---
> >   fs/jbd2/commit.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> > index 5b9408e3b370..ac7f067b7bdd 100644
> > --- a/fs/jbd2/commit.c
> > +++ b/fs/jbd2/commit.c
> > @@ -488,7 +488,6 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >   	jbd2_journal_wait_updates(journal);
> >   	commit_transaction->t_state = T_SWITCH;
> > -	write_unlock(&journal->j_state_lock);
> >   	J_ASSERT (atomic_read(&commit_transaction->t_outstanding_credits) <=
> >   			journal->j_max_transaction_buffers);
> > @@ -508,6 +507,8 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >   	 * has reserved.  This is consistent with the existing behaviour
> >   	 * that multiple jbd2_journal_get_write_access() calls to the same
> >   	 * buffer are perfectly permissible.
> > +	 * We use journal->j_state_lock here to serialize processing of
> > +	 * t_reserved_list with eviction of buffers from journal_unmap_buffer().
> >   	 */
> >   	while (commit_transaction->t_reserved_list) {
> >   		jh = commit_transaction->t_reserved_list;
> > @@ -527,6 +528,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >   		jbd2_journal_refile_buffer(journal, jh);
> >   	}
> > +	write_unlock(&journal->j_state_lock);
> >   	/*
> >   	 * Now try to drop any written-back buffers from the journal's
> >   	 * checkpoint lists.  We do this *before* commit because it potentially
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR