* [PATCH] binfmt_misc: Node could be NULL when evicting inode
@ 2017-10-10 10:06 Eryu Guan
2017-10-10 12:46 ` Oleg Nesterov
0 siblings, 1 reply; 3+ messages in thread
From: Eryu Guan @ 2017-10-10 10:06 UTC (permalink / raw)
To: linux-fsdevel; +Cc: Alexander Viro, Eryu Guan, Oleg Nesterov
inode->i_private is assigned by a Node pointer only after
registering a new binary format, so it could be NULL if we only
mount binfmt_misc but don't register any format, and this results in
NULL pointer dereference at umount time. e.g.
mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc
umount /proc/sys/fs/binfmt_misc
[ 9379.678259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000013
[ 9379.985952] IP: bm_evict_inode+0x16/0x40 [binfmt_misc]
...
[ 9380.964911] Call Trace:
[ 9380.977633] evict+0xd3/0x1a0
[ 9380.994449] iput+0x17d/0x1d0
[ 9381.010306] dentry_unlink_inode+0xb9/0xf0
[ 9381.034046] __dentry_kill+0xc7/0x170
[ 9381.055145] shrink_dentry_list+0x122/0x280
[ 9381.078908] shrink_dcache_parent+0x39/0x90
[ 9381.103082] do_one_tree+0x12/0x40
[ 9381.122005] shrink_dcache_for_umount+0x2d/0x90
[ 9381.146517] generic_shutdown_super+0x1f/0x120
[ 9381.171644] kill_litter_super+0x29/0x40
[ 9381.193513] deactivate_locked_super+0x43/0x70
[ 9381.219177] deactivate_super+0x45/0x60
[ 9381.240130] cleanup_mnt+0x3f/0x70
[ 9381.259064] __cleanup_mnt+0x12/0x20
[ 9381.279802] task_work_run+0x86/0xa0
[ 9381.299612] exit_to_usermode_loop+0x6d/0x99
[ 9381.323872] syscall_return_slowpath+0xba/0xf0
[ 9381.350464] entry_SYSCALL_64_fastpath+0xa3/0xa
Fix it by making sure Node (e) is not NULL.
Cc: Oleg Nesterov <oleg@redhat.com>
Fixes: 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()")
Signed-off-by: Eryu Guan <eguan@redhat.com>
---
fs/binfmt_misc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 2a46762def31..a7c5a9861bef 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -596,7 +596,7 @@ static void bm_evict_inode(struct inode *inode)
{
Node *e = inode->i_private;
- if (e->flags & MISC_FMT_OPEN_FILE)
+ if (e && e->flags & MISC_FMT_OPEN_FILE)
filp_close(e->interp_file, NULL);
clear_inode(inode);
--
2.13.6
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] binfmt_misc: Node could be NULL when evicting inode
2017-10-10 10:06 [PATCH] binfmt_misc: Node could be NULL when evicting inode Eryu Guan
@ 2017-10-10 12:46 ` Oleg Nesterov
2017-10-10 16:25 ` Oleg Nesterov
0 siblings, 1 reply; 3+ messages in thread
From: Oleg Nesterov @ 2017-10-10 12:46 UTC (permalink / raw)
To: Eryu Guan, Andrew Morton
Cc: linux-fsdevel, Alexander Viro, Tycho Andersen, chandan, Kees Cook,
linux-kernel
On 10/10, Eryu Guan wrote:
>
> inode->i_private is assigned by a Node pointer only after
> registering a new binary format, so it could be NULL if we only
> mount binfmt_misc but don't register any format,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Not really, I 'think... I mean, the problem is that e == NULL when inode
is root_inode, or "status", or "register", created by bm_fill_super()...
Yes, you need to unregister all formats to hit this problem.
Oh, and I'm afraid I intoduced another problem, bm_register_write() error
paths can call iput() with MISC_FMT_OPEN_FILE set but e->interpreter == NULL.
I'll re-check and send another patch today.
Thanks a lot!
Acked-by: Oleg Nesterov <oleg@redhat.com>
> and this results in
> NULL pointer dereference at umount time. e.g.
>
> mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc
> umount /proc/sys/fs/binfmt_misc
>
> [ 9379.678259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000013
> [ 9379.985952] IP: bm_evict_inode+0x16/0x40 [binfmt_misc]
> ...
> [ 9380.964911] Call Trace:
> [ 9380.977633] evict+0xd3/0x1a0
> [ 9380.994449] iput+0x17d/0x1d0
> [ 9381.010306] dentry_unlink_inode+0xb9/0xf0
> [ 9381.034046] __dentry_kill+0xc7/0x170
> [ 9381.055145] shrink_dentry_list+0x122/0x280
> [ 9381.078908] shrink_dcache_parent+0x39/0x90
> [ 9381.103082] do_one_tree+0x12/0x40
> [ 9381.122005] shrink_dcache_for_umount+0x2d/0x90
> [ 9381.146517] generic_shutdown_super+0x1f/0x120
> [ 9381.171644] kill_litter_super+0x29/0x40
> [ 9381.193513] deactivate_locked_super+0x43/0x70
> [ 9381.219177] deactivate_super+0x45/0x60
> [ 9381.240130] cleanup_mnt+0x3f/0x70
> [ 9381.259064] __cleanup_mnt+0x12/0x20
> [ 9381.279802] task_work_run+0x86/0xa0
> [ 9381.299612] exit_to_usermode_loop+0x6d/0x99
> [ 9381.323872] syscall_return_slowpath+0xba/0xf0
> [ 9381.350464] entry_SYSCALL_64_fastpath+0xa3/0xa
>
> Fix it by making sure Node (e) is not NULL.
>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Fixes: 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()")
> Signed-off-by: Eryu Guan <eguan@redhat.com>
> ---
> fs/binfmt_misc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
> index 2a46762def31..a7c5a9861bef 100644
> --- a/fs/binfmt_misc.c
> +++ b/fs/binfmt_misc.c
> @@ -596,7 +596,7 @@ static void bm_evict_inode(struct inode *inode)
> {
> Node *e = inode->i_private;
>
> - if (e->flags & MISC_FMT_OPEN_FILE)
> + if (e && e->flags & MISC_FMT_OPEN_FILE)
> filp_close(e->interp_file, NULL);
>
> clear_inode(inode);
> --
> 2.13.6
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] binfmt_misc: Node could be NULL when evicting inode
2017-10-10 12:46 ` Oleg Nesterov
@ 2017-10-10 16:25 ` Oleg Nesterov
0 siblings, 0 replies; 3+ messages in thread
From: Oleg Nesterov @ 2017-10-10 16:25 UTC (permalink / raw)
To: Eryu Guan, Andrew Morton
Cc: linux-fsdevel, Alexander Viro, Tycho Andersen, chandan, Kees Cook,
linux-kernel
On 10/10, Oleg Nesterov wrote:
>
> On 10/10, Eryu Guan wrote:
> >
> > inode->i_private is assigned by a Node pointer only after
> > registering a new binary format, so it could be NULL if we only
> > mount binfmt_misc but don't register any format,
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Not really, I 'think... I mean, the problem is that e == NULL when inode
> is root_inode, or "status", or "register", created by bm_fill_super()...
>
> Yes, you need to unregister all formats to hit this problem.
>
>
> Oh, and I'm afraid I intoduced another problem, bm_register_write() error
> paths can call iput() with MISC_FMT_OPEN_FILE set but e->interpreter == NULL.
> I'll re-check and send another patch today.
Ah, no, I was wrong again... If bm_register_write() fails, bm_evict_inode()
will hit the same ->i_private == NULL problem fixed by your patch.
So the changelog can be updated to explain that i_private == NULL is possible
if inode was created by bm_fill_super(), or iput() was called by the error path
in bm_register_write().
But the patch is obviously fine, thanks again.
> Thanks a lot!
>
>
> Acked-by: Oleg Nesterov <oleg@redhat.com>
>
>
> > and this results in
> > NULL pointer dereference at umount time. e.g.
> >
> > mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc
> > umount /proc/sys/fs/binfmt_misc
> >
> > [ 9379.678259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000013
> > [ 9379.985952] IP: bm_evict_inode+0x16/0x40 [binfmt_misc]
> > ...
> > [ 9380.964911] Call Trace:
> > [ 9380.977633] evict+0xd3/0x1a0
> > [ 9380.994449] iput+0x17d/0x1d0
> > [ 9381.010306] dentry_unlink_inode+0xb9/0xf0
> > [ 9381.034046] __dentry_kill+0xc7/0x170
> > [ 9381.055145] shrink_dentry_list+0x122/0x280
> > [ 9381.078908] shrink_dcache_parent+0x39/0x90
> > [ 9381.103082] do_one_tree+0x12/0x40
> > [ 9381.122005] shrink_dcache_for_umount+0x2d/0x90
> > [ 9381.146517] generic_shutdown_super+0x1f/0x120
> > [ 9381.171644] kill_litter_super+0x29/0x40
> > [ 9381.193513] deactivate_locked_super+0x43/0x70
> > [ 9381.219177] deactivate_super+0x45/0x60
> > [ 9381.240130] cleanup_mnt+0x3f/0x70
> > [ 9381.259064] __cleanup_mnt+0x12/0x20
> > [ 9381.279802] task_work_run+0x86/0xa0
> > [ 9381.299612] exit_to_usermode_loop+0x6d/0x99
> > [ 9381.323872] syscall_return_slowpath+0xba/0xf0
> > [ 9381.350464] entry_SYSCALL_64_fastpath+0xa3/0xa
> >
> > Fix it by making sure Node (e) is not NULL.
> >
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Fixes: 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()")
> > Signed-off-by: Eryu Guan <eguan@redhat.com>
> > ---
> > fs/binfmt_misc.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
> > index 2a46762def31..a7c5a9861bef 100644
> > --- a/fs/binfmt_misc.c
> > +++ b/fs/binfmt_misc.c
> > @@ -596,7 +596,7 @@ static void bm_evict_inode(struct inode *inode)
> > {
> > Node *e = inode->i_private;
> >
> > - if (e->flags & MISC_FMT_OPEN_FILE)
> > + if (e && e->flags & MISC_FMT_OPEN_FILE)
> > filp_close(e->interp_file, NULL);
> >
> > clear_inode(inode);
> > --
> > 2.13.6
> >
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-10-10 10:06 [PATCH] binfmt_misc: Node could be NULL when evicting inode Eryu Guan
2017-10-10 12:46 ` Oleg Nesterov
2017-10-10 16:25 ` Oleg Nesterov
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