* [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
@ 2018-10-04 10:46 Jan Kara
2018-10-04 11:50 ` Lukas Czerner
` (2 more replies)
0 siblings, 3 replies; 9+ messages in thread
From: Jan Kara @ 2018-10-04 10:46 UTC (permalink / raw)
To: Ted Tso; +Cc: linux-ext4, Jan Kara, stable
The code cleaning transaction's lists of checkpoint buffers has a bug
where it increases bh refcount only after releasing
journal->j_list_lock. Thus the following race is possible:
CPU0 CPU1
jbd2_log_do_checkpoint()
jbd2_journal_try_to_free_buffers()
__journal_try_to_free_buffer(bh)
...
while (transaction->t_checkpoint_io_list)
...
if (buffer_locked(bh)) {
<-- IO completes now, buffer gets unlocked -->
spin_unlock(&journal->j_list_lock);
spin_lock(&journal->j_list_lock);
__jbd2_journal_remove_checkpoint(jh);
spin_unlock(&journal->j_list_lock);
try_to_free_buffers(page);
get_bh(bh) <-- accesses freed bh
Fix the problem by grabbing bh reference before unlocking
journal->j_list_lock.
Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
Fixes: be1158cc615fd723552f0d9912087423c7cadda5
Reported-by: syzbot+7f4a27091759e2fe7453@syzkaller.appspotmail.com
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/jbd2/checkpoint.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index c125d662777c..26f8d7e46462 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -251,8 +251,8 @@ int jbd2_log_do_checkpoint(journal_t *journal)
bh = jh2bh(jh);
if (buffer_locked(bh)) {
- spin_unlock(&journal->j_list_lock);
get_bh(bh);
+ spin_unlock(&journal->j_list_lock);
wait_on_buffer(bh);
/* the journal_head may have gone by now */
BUFFER_TRACE(bh, "brelse");
@@ -333,8 +333,8 @@ int jbd2_log_do_checkpoint(journal_t *journal)
jh = transaction->t_checkpoint_io_list;
bh = jh2bh(jh);
if (buffer_locked(bh)) {
- spin_unlock(&journal->j_list_lock);
get_bh(bh);
+ spin_unlock(&journal->j_list_lock);
wait_on_buffer(bh);
/* the journal_head may have gone by now */
BUFFER_TRACE(bh, "brelse");
--
2.16.4
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 10:46 [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint() Jan Kara
@ 2018-10-04 11:50 ` Lukas Czerner
2018-10-04 12:30 ` Jan Kara
2018-10-04 15:44 ` Greg KH
2018-10-05 22:57 ` Theodore Y. Ts'o
2 siblings, 1 reply; 9+ messages in thread
From: Lukas Czerner @ 2018-10-04 11:50 UTC (permalink / raw)
To: Jan Kara; +Cc: Ted Tso, linux-ext4, stable
On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> The code cleaning transaction's lists of checkpoint buffers has a bug
> where it increases bh refcount only after releasing
> journal->j_list_lock. Thus the following race is possible:
>
> CPU0 CPU1
> jbd2_log_do_checkpoint()
> jbd2_journal_try_to_free_buffers()
> __journal_try_to_free_buffer(bh)
> ...
> while (transaction->t_checkpoint_io_list)
> ...
> if (buffer_locked(bh)) {
>
> <-- IO completes now, buffer gets unlocked -->
>
> spin_unlock(&journal->j_list_lock);
> spin_lock(&journal->j_list_lock);
> __jbd2_journal_remove_checkpoint(jh);
> spin_unlock(&journal->j_list_lock);
> try_to_free_buffers(page);
> get_bh(bh) <-- accesses freed bh
>
> Fix the problem by grabbing bh reference before unlocking
> journal->j_list_lock.
Hi Jan,
nice catch. The patch looks good, you can add
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Btw, do you by any chance have a reproducer for this ?
-Lukas
>
> Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> Fixes: be1158cc615fd723552f0d9912087423c7cadda5
> Reported-by: syzbot+7f4a27091759e2fe7453@syzkaller.appspotmail.com
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/jbd2/checkpoint.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index c125d662777c..26f8d7e46462 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -251,8 +251,8 @@ int jbd2_log_do_checkpoint(journal_t *journal)
> bh = jh2bh(jh);
>
> if (buffer_locked(bh)) {
> - spin_unlock(&journal->j_list_lock);
> get_bh(bh);
> + spin_unlock(&journal->j_list_lock);
> wait_on_buffer(bh);
> /* the journal_head may have gone by now */
> BUFFER_TRACE(bh, "brelse");
> @@ -333,8 +333,8 @@ int jbd2_log_do_checkpoint(journal_t *journal)
> jh = transaction->t_checkpoint_io_list;
> bh = jh2bh(jh);
> if (buffer_locked(bh)) {
> - spin_unlock(&journal->j_list_lock);
> get_bh(bh);
> + spin_unlock(&journal->j_list_lock);
> wait_on_buffer(bh);
> /* the journal_head may have gone by now */
> BUFFER_TRACE(bh, "brelse");
> --
> 2.16.4
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 11:50 ` Lukas Czerner
@ 2018-10-04 12:30 ` Jan Kara
0 siblings, 0 replies; 9+ messages in thread
From: Jan Kara @ 2018-10-04 12:30 UTC (permalink / raw)
To: Lukas Czerner; +Cc: Jan Kara, Ted Tso, linux-ext4, stable
On Thu 04-10-18 13:50:12, Lukas Czerner wrote:
> On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> > The code cleaning transaction's lists of checkpoint buffers has a bug
> > where it increases bh refcount only after releasing
> > journal->j_list_lock. Thus the following race is possible:
> >
> > CPU0 CPU1
> > jbd2_log_do_checkpoint()
> > jbd2_journal_try_to_free_buffers()
> > __journal_try_to_free_buffer(bh)
> > ...
> > while (transaction->t_checkpoint_io_list)
> > ...
> > if (buffer_locked(bh)) {
> >
> > <-- IO completes now, buffer gets unlocked -->
> >
> > spin_unlock(&journal->j_list_lock);
> > spin_lock(&journal->j_list_lock);
> > __jbd2_journal_remove_checkpoint(jh);
> > spin_unlock(&journal->j_list_lock);
> > try_to_free_buffers(page);
> > get_bh(bh) <-- accesses freed bh
> >
> > Fix the problem by grabbing bh reference before unlocking
> > journal->j_list_lock.
>
> Hi Jan,
>
> nice catch. The patch looks good, you can add
>
> Reviewed-by: Lukas Czerner <lczerner@redhat.com>
>
> Btw, do you by any chance have a reproducer for this ?
No, syzbot hit it but the race window is really small so I don't think you
can create reasonably reliable reproducer...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 10:46 [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint() Jan Kara
2018-10-04 11:50 ` Lukas Czerner
@ 2018-10-04 15:44 ` Greg KH
2018-10-04 16:05 ` Jan Kara
2018-10-05 22:57 ` Theodore Y. Ts'o
2 siblings, 1 reply; 9+ messages in thread
From: Greg KH @ 2018-10-04 15:44 UTC (permalink / raw)
To: Jan Kara; +Cc: Ted Tso, linux-ext4, stable
On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> The code cleaning transaction's lists of checkpoint buffers has a bug
> where it increases bh refcount only after releasing
> journal->j_list_lock. Thus the following race is possible:
>
> CPU0 CPU1
> jbd2_log_do_checkpoint()
> jbd2_journal_try_to_free_buffers()
> __journal_try_to_free_buffer(bh)
> ...
> while (transaction->t_checkpoint_io_list)
> ...
> if (buffer_locked(bh)) {
>
> <-- IO completes now, buffer gets unlocked -->
>
> spin_unlock(&journal->j_list_lock);
> spin_lock(&journal->j_list_lock);
> __jbd2_journal_remove_checkpoint(jh);
> spin_unlock(&journal->j_list_lock);
> try_to_free_buffers(page);
> get_bh(bh) <-- accesses freed bh
>
> Fix the problem by grabbing bh reference before unlocking
> journal->j_list_lock.
>
> Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> Fixes: be1158cc615fd723552f0d9912087423c7cadda5
Nit, this normally looks like:
Fixes: dc6e8d669cf5 ("jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()")
And this is created by:
git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"
thanks
greg k-h
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 15:44 ` Greg KH
@ 2018-10-04 16:05 ` Jan Kara
2018-10-04 16:33 ` Lukas Czerner
2018-10-04 21:22 ` Theodore Y. Ts'o
0 siblings, 2 replies; 9+ messages in thread
From: Jan Kara @ 2018-10-04 16:05 UTC (permalink / raw)
To: Greg KH; +Cc: Jan Kara, Ted Tso, linux-ext4, stable
On Thu 04-10-18 08:44:02, Greg KH wrote:
> On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> > The code cleaning transaction's lists of checkpoint buffers has a bug
> > where it increases bh refcount only after releasing
> > journal->j_list_lock. Thus the following race is possible:
> >
> > CPU0 CPU1
> > jbd2_log_do_checkpoint()
> > jbd2_journal_try_to_free_buffers()
> > __journal_try_to_free_buffer(bh)
> > ...
> > while (transaction->t_checkpoint_io_list)
> > ...
> > if (buffer_locked(bh)) {
> >
> > <-- IO completes now, buffer gets unlocked -->
> >
> > spin_unlock(&journal->j_list_lock);
> > spin_lock(&journal->j_list_lock);
> > __jbd2_journal_remove_checkpoint(jh);
> > spin_unlock(&journal->j_list_lock);
> > try_to_free_buffers(page);
> > get_bh(bh) <-- accesses freed bh
> >
> > Fix the problem by grabbing bh reference before unlocking
> > journal->j_list_lock.
> >
> > Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> > Fixes: be1158cc615fd723552f0d9912087423c7cadda5
>
> Nit, this normally looks like:
>
> Fixes: dc6e8d669cf5 ("jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()")
>
> And this is created by:
> git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"
OK, ok, will do next time. The full git commit ID is faster to cut-n-paste
which shows how lazy I'm ;)
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 16:05 ` Jan Kara
@ 2018-10-04 16:33 ` Lukas Czerner
2018-10-04 21:22 ` Theodore Y. Ts'o
1 sibling, 0 replies; 9+ messages in thread
From: Lukas Czerner @ 2018-10-04 16:33 UTC (permalink / raw)
To: Jan Kara; +Cc: Greg KH, Ted Tso, linux-ext4, stable
On Thu, Oct 04, 2018 at 06:05:46PM +0200, Jan Kara wrote:
> On Thu 04-10-18 08:44:02, Greg KH wrote:
> > On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> > > The code cleaning transaction's lists of checkpoint buffers has a bug
> > > where it increases bh refcount only after releasing
> > > journal->j_list_lock. Thus the following race is possible:
> > >
> > > CPU0 CPU1
> > > jbd2_log_do_checkpoint()
> > > jbd2_journal_try_to_free_buffers()
> > > __journal_try_to_free_buffer(bh)
> > > ...
> > > while (transaction->t_checkpoint_io_list)
> > > ...
> > > if (buffer_locked(bh)) {
> > >
> > > <-- IO completes now, buffer gets unlocked -->
> > >
> > > spin_unlock(&journal->j_list_lock);
> > > spin_lock(&journal->j_list_lock);
> > > __jbd2_journal_remove_checkpoint(jh);
> > > spin_unlock(&journal->j_list_lock);
> > > try_to_free_buffers(page);
> > > get_bh(bh) <-- accesses freed bh
> > >
> > > Fix the problem by grabbing bh reference before unlocking
> > > journal->j_list_lock.
> > >
> > > Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> > > Fixes: be1158cc615fd723552f0d9912087423c7cadda5
> >
> > Nit, this normally looks like:
> >
> > Fixes: dc6e8d669cf5 ("jbd2: don't call get_bh() before calling __jbd2_journal_remove_checkpoint()")
> >
> > And this is created by:
> > git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"
>
> OK, ok, will do next time. The full git commit ID is faster to cut-n-paste
> which shows how lazy I'm ;)
I have this in the .gitconfig
[pretty]
fixes = Fixes: %h (\"%s\")
which helps. I think I found it in the docs somewhere.
-Lukas
>
> Honza
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 16:05 ` Jan Kara
2018-10-04 16:33 ` Lukas Czerner
@ 2018-10-04 21:22 ` Theodore Y. Ts'o
2018-10-05 9:18 ` Jan Kara
1 sibling, 1 reply; 9+ messages in thread
From: Theodore Y. Ts'o @ 2018-10-04 21:22 UTC (permalink / raw)
To: Jan Kara; +Cc: Greg KH, linux-ext4, stable
On Thu, Oct 04, 2018 at 06:05:46PM +0200, Jan Kara wrote:
>
> OK, ok, will do next time. The full git commit ID is faster to cut-n-paste
> which shows how lazy I'm ;)
No worires, I'll fix that up for you when I apply it.
- Ted
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 21:22 ` Theodore Y. Ts'o
@ 2018-10-05 9:18 ` Jan Kara
0 siblings, 0 replies; 9+ messages in thread
From: Jan Kara @ 2018-10-05 9:18 UTC (permalink / raw)
To: Theodore Y. Ts'o; +Cc: Jan Kara, Greg KH, linux-ext4, stable
On Thu 04-10-18 17:22:18, Theodore Y. Ts'o wrote:
> On Thu, Oct 04, 2018 at 06:05:46PM +0200, Jan Kara wrote:
> >
> > OK, ok, will do next time. The full git commit ID is faster to cut-n-paste
> > which shows how lazy I'm ;)
>
> No worires, I'll fix that up for you when I apply it.
Thanks!
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint()
2018-10-04 10:46 [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint() Jan Kara
2018-10-04 11:50 ` Lukas Czerner
2018-10-04 15:44 ` Greg KH
@ 2018-10-05 22:57 ` Theodore Y. Ts'o
2 siblings, 0 replies; 9+ messages in thread
From: Theodore Y. Ts'o @ 2018-10-05 22:57 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-ext4, stable
On Thu, Oct 04, 2018 at 12:46:40PM +0200, Jan Kara wrote:
> The code cleaning transaction's lists of checkpoint buffers has a bug
> where it increases bh refcount only after releasing
> journal->j_list_lock. Thus the following race is possible:
>
> CPU0 CPU1
> jbd2_log_do_checkpoint()
> jbd2_journal_try_to_free_buffers()
> __journal_try_to_free_buffer(bh)
> ...
> while (transaction->t_checkpoint_io_list)
> ...
> if (buffer_locked(bh)) {
>
> <-- IO completes now, buffer gets unlocked -->
>
> spin_unlock(&journal->j_list_lock);
> spin_lock(&journal->j_list_lock);
> __jbd2_journal_remove_checkpoint(jh);
> spin_unlock(&journal->j_list_lock);
> try_to_free_buffers(page);
> get_bh(bh) <-- accesses freed bh
>
> Fix the problem by grabbing bh reference before unlocking
> journal->j_list_lock.
>
> Fixes: dc6e8d669cf5cb3ff84707c372c0a2a8a5e80845
> Fixes: be1158cc615fd723552f0d9912087423c7cadda5
> Reported-by: syzbot+7f4a27091759e2fe7453@syzkaller.appspotmail.com
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>
Applied, thanks (with the Fixes field adjusted).
- Ted
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2018-10-06 5:57 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-04 10:46 [PATCH] jbd2: Fix use after free in jbd2_log_do_checkpoint() Jan Kara
2018-10-04 11:50 ` Lukas Czerner
2018-10-04 12:30 ` Jan Kara
2018-10-04 15:44 ` Greg KH
2018-10-04 16:05 ` Jan Kara
2018-10-04 16:33 ` Lukas Czerner
2018-10-04 21:22 ` Theodore Y. Ts'o
2018-10-05 9:18 ` Jan Kara
2018-10-05 22:57 ` Theodore Y. Ts'o
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