* [PATCH v2] ext4: fix use-after-free in dx_release()
@ 2019-05-08 8:34 Sahitya Tummala
2019-05-08 8:49 ` Andreas Dilger
2019-05-11 2:01 ` Theodore Ts'o
0 siblings, 2 replies; 3+ messages in thread
From: Sahitya Tummala @ 2019-05-08 8:34 UTC (permalink / raw)
To: Theodore Ts'o, Andreas Dilger, linux-ext4
Cc: linux-kernel, Sahitya Tummala
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 ffffffc17ac3e01e
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 <stummala@codeaurora.org>
---
v2:
add a comment in dx_release()
fs/ext4/namei.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 980166a..5d9ffa8 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -871,12 +871,15 @@ 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++) {
+ /* save local copy, "info" may be freed after brelse() */
+ 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.
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] ext4: fix use-after-free in dx_release()
2019-05-08 8:34 [PATCH v2] ext4: fix use-after-free in dx_release() Sahitya Tummala
@ 2019-05-08 8:49 ` Andreas Dilger
2019-05-11 2:01 ` Theodore Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Andreas Dilger @ 2019-05-08 8:49 UTC (permalink / raw)
To: Sahitya Tummala; +Cc: Theodore Ts'o, linux-ext4, linux-kernel
[-- Attachment #1: Type: text/plain, Size: 1864 bytes --]
On May 8, 2019, at 2:34 AM, Sahitya Tummala <stummala@codeaurora.org> 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 ffffffc17ac3e01e
> 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 <stummala@codeaurora.org>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
> ---
> v2:
> add a comment in dx_release()
>
> fs/ext4/namei.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 980166a..5d9ffa8 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -871,12 +871,15 @@ 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++) {
> + /* save local copy, "info" may be freed after brelse() */
> + 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
[-- Attachment #2: Message signed with OpenPGP --]
[-- Type: application/pgp-signature, Size: 873 bytes --]
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] ext4: fix use-after-free in dx_release()
2019-05-08 8:34 [PATCH v2] ext4: fix use-after-free in dx_release() Sahitya Tummala
2019-05-08 8:49 ` Andreas Dilger
@ 2019-05-11 2:01 ` Theodore Ts'o
1 sibling, 0 replies; 3+ messages in thread
From: Theodore Ts'o @ 2019-05-11 2:01 UTC (permalink / raw)
To: Sahitya Tummala; +Cc: Andreas Dilger, linux-ext4, linux-kernel
On Wed, May 08, 2019 at 02:04:03PM +0530, 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 ffffffc17ac3e01e
> 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 <stummala@codeaurora.org>
Nice catch. Thanks, applied.
- Ted
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-05-11 17:19 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-08 8:34 [PATCH v2] ext4: fix use-after-free in dx_release() Sahitya Tummala
2019-05-08 8:49 ` Andreas Dilger
2019-05-11 2:01 ` Theodore Ts'o
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).