Re: [PATCH] ext4: fix use-after-free in dx_release()
On Wed, May 08, 2019 at 01:09:47AM -0600, Andreas Dilger wrote:
> On May 8, 2019, at 12:13 AM, Sahitya Tummala wrote:
> >
> > The buffer_head (frames[0].bh) and it's corresping page can be
> > potentially free'd once brelse() is done inside the for loop
> > but before the for loop exits in dx_release(). It can be free'd
> > in another context, when the page cache is flushed via
> > drop_caches_sysctl_handler(). This results into below data abort
> > when accessing info->indirect_levels in dx_release().
> >
> > Unable to handle kernel paging request at virtual address ffc17ac3e01e
> > Call trace:
> > dx_release+0x70/0x90
> > ext4_htree_fill_tree+0x2d4/0x300
> > ext4_readdir+0x244/0x6f8
> > iterate_dir+0xbc/0x160
> > SyS_getdents64+0x94/0x174
> >
> > Signed-off-by: Sahitya Tummala
>
> The patch looks reasonable, but there is a danger that it may be
> "optimized" back to the pre-patch form again. It probably makes
> sense to include a comment like:
>
> /* save local copy, "info" may be freed after brelse() */
Thanks for reviewing it. Sure, I will add the comment.
>
> Looks fine otherwise.
>
> Reviewed-by: Andreas Dilger
>
> > ---
> > fs/ext4/namei.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > index 4181c9c..7e6c298 100644
> > --- a/fs/ext4/namei.c
> > +++ b/fs/ext4/namei.c
> > @@ -871,12 +871,14 @@ static void dx_release(struct dx_frame *frames)
> > {
> > struct dx_root_info *info;
> > int i;
> > + unsigned int indirect_levels;
> >
> > if (frames[0].bh == NULL)
> > return;
> >
> > info = &((struct dx_root *)frames[0].bh->b_data)->info;
> > - for (i = 0; i <= info->indirect_levels; i++) {
> > + indirect_levels = info->indirect_levels;
> > + for (i = 0; i <= indirect_levels; i++) {
> > if (frames[i].bh == NULL)
> > break;
> > brelse(frames[i].bh);
> > --
> > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
> > Inc.
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> > Foundation Collaborative Project.
> >
>
>
> Cheers, Andreas
>
>
>
>
>
--
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
Re: [PATCH] ext4: fix use-after-free in dx_release()
On May 8, 2019, at 12:13 AM, Sahitya Tummala wrote:
>
> The buffer_head (frames[0].bh) and it's corresping page can be
> potentially free'd once brelse() is done inside the for loop
> but before the for loop exits in dx_release(). It can be free'd
> in another context, when the page cache is flushed via
> drop_caches_sysctl_handler(). This results into below data abort
> when accessing info->indirect_levels in dx_release().
>
> Unable to handle kernel paging request at virtual address ffc17ac3e01e
> Call trace:
> dx_release+0x70/0x90
> ext4_htree_fill_tree+0x2d4/0x300
> ext4_readdir+0x244/0x6f8
> iterate_dir+0xbc/0x160
> SyS_getdents64+0x94/0x174
>
> Signed-off-by: Sahitya Tummala
The patch looks reasonable, but there is a danger that it may be
"optimized" back to the pre-patch form again. It probably makes
sense to include a comment like:
/* save local copy, "info" may be freed after brelse() */
Looks fine otherwise.
Reviewed-by: Andreas Dilger
> ---
> fs/ext4/namei.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 4181c9c..7e6c298 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -871,12 +871,14 @@ static void dx_release(struct dx_frame *frames)
> {
> struct dx_root_info *info;
> int i;
> + unsigned int indirect_levels;
>
> if (frames[0].bh == NULL)
> return;
>
> info = &((struct dx_root *)frames[0].bh->b_data)->info;
> - for (i = 0; i <= info->indirect_levels; i++) {
> + indirect_levels = info->indirect_levels;
> + for (i = 0; i <= indirect_levels; i++) {
> if (frames[i].bh == NULL)
> break;
> brelse(frames[i].bh);
> --
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project.
>
Cheers, Andreas
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[PATCH] ext4: fix use-after-free in dx_release()
The buffer_head (frames[0].bh) and it's corresping page can be
potentially free'd once brelse() is done inside the for loop
but before the for loop exits in dx_release(). It can be free'd
in another context, when the page cache is flushed via
drop_caches_sysctl_handler(). This results into below data abort
when accessing info->indirect_levels in dx_release().
Unable to handle kernel paging request at virtual address ffc17ac3e01e
Call trace:
dx_release+0x70/0x90
ext4_htree_fill_tree+0x2d4/0x300
ext4_readdir+0x244/0x6f8
iterate_dir+0xbc/0x160
SyS_getdents64+0x94/0x174
Signed-off-by: Sahitya Tummala
---
fs/ext4/namei.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 4181c9c..7e6c298 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -871,12 +871,14 @@ static void dx_release(struct dx_frame *frames)
{
struct dx_root_info *info;
int i;
+ unsigned int indirect_levels;
if (frames[0].bh == NULL)
return;
info = &((struct dx_root *)frames[0].bh->b_data)->info;
- for (i = 0; i <= info->indirect_levels; i++) {
+ indirect_levels = info->indirect_levels;
+ for (i = 0; i <= indirect_levels; i++) {
if (frames[i].bh == NULL)
break;
brelse(frames[i].bh);
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project.
