2018-11-26 03:09:46

by Pan Bian

Subject: [PATCH] nilfs2: fix potential use after free

brelse(bh) is called to drop the reference count of bh when the call
to nilfs_dat_translate fails. If the reference count hits 0, bh may be
freed. However, bh->b_page is unlocked and put after that, which may
result in a use-after-free bug. This patch moves the release operation
after unlocking and putting the page.

Signed-off-by: Pan Bian <[email protected]>
---
fs/nilfs2/gcinode.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nilfs2/gcinode.c b/fs/nilfs2/gcinode.c
index aa3c328..a24bb29 100644
--- a/fs/nilfs2/gcinode.c
+++ b/fs/nilfs2/gcinode.c
@@ -73,10 +73,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
struct the_nilfs *nilfs = inode->i_sb->s_fs_info;

err = nilfs_dat_translate(nilfs->ns_dat, vbn, &pbn);
- if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
- brelse(bh);
+ if (unlikely(err)) /* -EIO, -ENOMEM, -ENOENT */
goto failed;
- }
}

lock_buffer(bh);
@@ -102,6 +100,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
failed:
unlock_page(bh->b_page);
put_page(bh->b_page);
+ if (unlikely(err))
+ brelse(bh);
return err;
}

--
2.7.4

2018-12-03 09:11:52

by Ryusuke Konishi

Subject: Re: [PATCH] nilfs2: fix potential use after free

Hi, Pan Bian

Thank you for feeding back this patch.
I reviewed this and am thinking this must be sent to upstream.

Did you see any kernel oops on this bug ?

Regards,
Ryusuke Konishi

On Mon, 26 Nov 2018 11:08:29 +0800, Pan Bian <[email protected]> wrote:
> brelse(bh) is called to drop the reference count of bh when the call
> to nilfs_dat_translate fails. If the reference count hits 0, bh may be
> freed. However, bh->b_page is unlocked and put after that, which may
> result in a use-after-free bug. This patch moves the release operation
> after unlocking and putting the page.
>
> Signed-off-by: Pan Bian <[email protected]>
> ---
> fs/nilfs2/gcinode.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nilfs2/gcinode.c b/fs/nilfs2/gcinode.c
> index aa3c328..a24bb29 100644
> --- a/fs/nilfs2/gcinode.c
> +++ b/fs/nilfs2/gcinode.c
> @@ -73,10 +73,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
> struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
>
> err = nilfs_dat_translate(nilfs->ns_dat, vbn, &pbn);
> - if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
> - brelse(bh);
> + if (unlikely(err)) /* -EIO, -ENOMEM, -ENOENT */
> goto failed;
> - }
> }
>
> lock_buffer(bh);
> @@ -102,6 +100,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
> failed:
> unlock_page(bh->b_page);
> put_page(bh->b_page);
> + if (unlikely(err))
> + brelse(bh);
> return err;
> }
>
> --
> 2.7.4
>
>

2018-12-03 09:16:02

by Pan Bian

Subject: Re: [PATCH] nilfs2: fix potential use after free

On Mon, Dec 03, 2018 at 06:10:51PM +0900, Ryusuke Konishi wrote:
> Hi, Pan Bian
>
> Thank you for feeding back this patch.
> I reviewed this and am thinking this must be sent to upstream.
>
> Did you see any kernel oops on this bug ?

Not yet. In fact, I found it with a static method.

Best regards,
Pan Bian

>
> Regards,
> Ryusuke Konishi
>
> On Mon, 26 Nov 2018 11:08:29 +0800, Pan Bian <[email protected]> wrote:
> > brelse(bh) is called to drop the reference count of bh when the call
> > to nilfs_dat_translate fails. If the reference count hits 0, bh may be
> > freed. However, bh->b_page is unlocked and put after that, which may
> > result in a use-after-free bug. This patch moves the release operation
> > after unlocking and putting the page.
> >
> > Signed-off-by: Pan Bian <[email protected]>
> > ---
> > fs/nilfs2/gcinode.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/nilfs2/gcinode.c b/fs/nilfs2/gcinode.c
> > index aa3c328..a24bb29 100644
> > --- a/fs/nilfs2/gcinode.c
> > +++ b/fs/nilfs2/gcinode.c
> > @@ -73,10 +73,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
> > struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
> >
> > err = nilfs_dat_translate(nilfs->ns_dat, vbn, &pbn);
> > - if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
> > - brelse(bh);
> > + if (unlikely(err)) /* -EIO, -ENOMEM, -ENOENT */
> > goto failed;
> > - }
> > }
> >
> > lock_buffer(bh);
> > @@ -102,6 +100,8 @@ int nilfs_gccache_submit_read_data(struct inode *inode, sector_t blkoff,
> > failed:
> > unlock_page(bh->b_page);
> > put_page(bh->b_page);
> > + if (unlikely(err))
> > + brelse(bh);
> > return err;
> > }
> >
> > --
> > 2.7.4
> >
> >