[v1] ocfs2: fix deadlock in ocfs2_get_system_file_inode

[PATCH 5.15.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

Posted by Pranav Tyagi 3 months, 1 week ago

From: Mohammed Anees <pvmohammedanees2003@gmail.com>

[ Upstream commit 7bf1823e010e8db2fb649c790bd1b449a75f52d8 ]

syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].

The scenario is depicted here,

	CPU0					CPU1
lock(&ocfs2_file_ip_alloc_sem_key);
                               lock(&osb->system_file_mutex);
                               lock(&ocfs2_file_ip_alloc_sem_key);
lock(&osb->system_file_mutex);

The function calls which could lead to this are:

CPU0
ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key);
.
.
.
ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);

CPU1 -
ocfs2_fill_super - lock(&osb->system_file_mutex);
.
.
.
ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);

This issue can be resolved by making the down_read -> down_read_try
in the ocfs2_read_virt_blocks.

[1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd

[ Backport to 5.15: context cleanly applied with no semantic changes.
Build-tested. ]

Link: https://lkml.kernel.org/r/20240924093257.7181-1-pvmohammedanees2003@gmail.com
Signed-off-by: Mohammed Anees <pvmohammedanees2003@gmail.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reported-by: <syzbot+e0055ea09f1f5e6fabdd@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
Tested-by: syzbot+e0055ea09f1f5e6fabdd@syzkaller.appspotmail.com
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc:  <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Tyagi <pranav.tyagi03@gmail.com>
---
 fs/ocfs2/extent_map.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index 70a768b623cf..f7672472fa82 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -973,7 +973,13 @@ int ocfs2_read_virt_blocks(struct inode *inode, u64 v_block, int nr,
 	}
 
 	while (done < nr) {
-		down_read(&OCFS2_I(inode)->ip_alloc_sem);
+		if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
+			rc = -EAGAIN;
+			mlog(ML_ERROR,
+				 "Inode #%llu ip_alloc_sem is temporarily unavailable\n",
+				 (unsigned long long)OCFS2_I(inode)->ip_blkno);
+			break;
+		}
 		rc = ocfs2_extent_map_get_blocks(inode, v_block + done,
 						 &p_block, &p_count, NULL);
 		up_read(&OCFS2_I(inode)->ip_alloc_sem);
-- 
2.49.0

Re: [PATCH 5.15.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

Posted by Greg KH 2 months, 3 weeks ago

On Mon, Jun 30, 2025 at 02:05:42PM +0530, Pranav Tyagi wrote:
> From: Mohammed Anees <pvmohammedanees2003@gmail.com>
> 
> [ Upstream commit 7bf1823e010e8db2fb649c790bd1b449a75f52d8 ]
> 
> syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].
> 
> The scenario is depicted here,
> 
> 	CPU0					CPU1
> lock(&ocfs2_file_ip_alloc_sem_key);
>                                lock(&osb->system_file_mutex);
>                                lock(&ocfs2_file_ip_alloc_sem_key);
> lock(&osb->system_file_mutex);
> 
> The function calls which could lead to this are:
> 
> CPU0
> ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key);
> .
> .
> .
> ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
> 
> CPU1 -
> ocfs2_fill_super - lock(&osb->system_file_mutex);
> .
> .
> .
> ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);
> 
> This issue can be resolved by making the down_read -> down_read_try
> in the ocfs2_read_virt_blocks.
> 
> [1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
> 
> [ Backport to 5.15: context cleanly applied with no semantic changes.
> Build-tested. ]

We can't take a 5.15.y version, without it being in 6.1.y first, sorry
:(

Re: [PATCH 5.15.y] ocfs2: fix deadlock in ocfs2_get_system_file_inode

Posted by Pranav Tyagi 2 months, 3 weeks ago

On Sat, Jul 12, 2025 at 7:16 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jun 30, 2025 at 02:05:42PM +0530, Pranav Tyagi wrote:
> > From: Mohammed Anees <pvmohammedanees2003@gmail.com>
> >
> > [ Upstream commit 7bf1823e010e8db2fb649c790bd1b449a75f52d8 ]
> >
> > syzbot has found a possible deadlock in ocfs2_get_system_file_inode [1].
> >
> > The scenario is depicted here,
> >
> >       CPU0                                    CPU1
> > lock(&ocfs2_file_ip_alloc_sem_key);
> >                                lock(&osb->system_file_mutex);
> >                                lock(&ocfs2_file_ip_alloc_sem_key);
> > lock(&osb->system_file_mutex);
> >
> > The function calls which could lead to this are:
> >
> > CPU0
> > ocfs2_mknod - lock(&ocfs2_file_ip_alloc_sem_key);
> > .
> > .
> > .
> > ocfs2_get_system_file_inode - lock(&osb->system_file_mutex);
> >
> > CPU1 -
> > ocfs2_fill_super - lock(&osb->system_file_mutex);
> > .
> > .
> > .
> > ocfs2_read_virt_blocks - lock(&ocfs2_file_ip_alloc_sem_key);
> >
> > This issue can be resolved by making the down_read -> down_read_try
> > in the ocfs2_read_virt_blocks.
> >
> > [1] https://syzkaller.appspot.com/bug?extid=e0055ea09f1f5e6fabdd
> >
> > [ Backport to 5.15: context cleanly applied with no semantic changes.
> > Build-tested. ]
>
> We can't take a 5.15.y version, without it being in 6.1.y first, sorry
> :(
>

Hi,

Thanks for pointing that out. I wasn’t aware of the 6.1.y prerequisite
for 5.15.y backports. Learned something new today. I’ll make sure to get
it into 6.1.y first.

Regards
Pranav Tyagi