[PATCH] mm: save/restore current->journal_info in handle_mm_fault

[PATCH] mm: save/restore current->journal_info in handle_mm_fault

[Yan, Zheng]

We recently got an Oops report:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: jbd2__journal_start+0x38/0x1a2
[...]
Call Trace:
  ext4_page_mkwrite+0x307/0x52b
  _ext4_get_block+0xd8/0xd8
  do_page_mkwrite+0x6e/0xd8
  handle_mm_fault+0x686/0xf9b
  mntput_no_expire+0x1f/0x21e
  __do_page_fault+0x21d/0x465
  dput+0x4a/0x2f7
  page_fault+0x22/0x30
  copy_user_generic_string+0x2c/0x40
  copy_page_to_iter+0x8c/0x2b8
  generic_file_read_iter+0x26e/0x845
  timerqueue_del+0x31/0x90
  ceph_read_iter+0x697/0xa33 [ceph]
  hrtimer_cancel+0x23/0x41
  futex_wait+0x1c8/0x24d
  get_futex_key+0x32c/0x39a
  __vfs_read+0xe0/0x130
  vfs_read.part.1+0x6c/0x123
  handle_mm_fault+0x831/0xf9b
  __fget+0x7e/0xbf
  SyS_read+0x4d/0xb5

ceph_read_iter() uses current->journal_info to pass context info to
ceph_readpages(). Because ceph_readpages() needs to know if its caller
has already gotten capability of using page cache (distinguish read
from readahead/fadvise). ceph_read_iter() set current->journal_info,
then calls generic_file_read_iter().

In above Oops, page fault happened when copying data to userspace.
Page fault handler called ext4_page_mkwrite(). Ext4 code read
current->journal_info and assumed it is journal handle.

I checked other filesystems, btrfs probably suffers similar problem
for its readpage. (page fault happens when write() copies data from
userspace memory and the memory is mapped to a file in btrfs.
verify_parent_transid() can be called during readpage)

Cc: stable@vger.kernel.org
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
---
 mm/memory.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index a728bed16c20..db2a50233c49 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4044,6 +4044,7 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 		unsigned int flags)
 {
 	int ret;
+	void *old_journal_info;
 
 	__set_current_state(TASK_RUNNING);
 
@@ -4065,11 +4066,24 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 	if (flags & FAULT_FLAG_USER)
 		mem_cgroup_oom_enable();
 
+	/*
+	 * Fault can happen when filesystem A's read_iter()/write_iter()
+	 * copies data to/from userspace. Filesystem A may have set
+	 * current->journal_info. If the userspace memory is MAP_SHARED
+	 * mapped to a file in filesystem B, we later may call filesystem
+	 * B's vm operation. Filesystem B may also want to read/set
+	 * current->journal_info.
+	 */
+	old_journal_info = current->journal_info;
+	current->journal_info = NULL;
+
 	if (unlikely(is_vm_hugetlb_page(vma)))
 		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
 	else
 		ret = __handle_mm_fault(vma, address, flags);
 
+	current->journal_info = old_journal_info;
+
 	if (flags & FAULT_FLAG_USER) {
 		mem_cgroup_oom_disable();
 		/*
-- 
2.13.6

Re: [PATCH] mm: save/restore current->journal_info in handle_mm_fault

[Michal Hocko]

On Thu 14-12-17 18:55:27, Yan, Zheng wrote:
> We recently got an Oops report:
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: jbd2__journal_start+0x38/0x1a2
> [...]
> Call Trace:
>   ext4_page_mkwrite+0x307/0x52b
>   _ext4_get_block+0xd8/0xd8
>   do_page_mkwrite+0x6e/0xd8
>   handle_mm_fault+0x686/0xf9b
>   mntput_no_expire+0x1f/0x21e
>   __do_page_fault+0x21d/0x465
>   dput+0x4a/0x2f7
>   page_fault+0x22/0x30
>   copy_user_generic_string+0x2c/0x40
>   copy_page_to_iter+0x8c/0x2b8
>   generic_file_read_iter+0x26e/0x845
>   timerqueue_del+0x31/0x90
>   ceph_read_iter+0x697/0xa33 [ceph]
>   hrtimer_cancel+0x23/0x41
>   futex_wait+0x1c8/0x24d
>   get_futex_key+0x32c/0x39a
>   __vfs_read+0xe0/0x130
>   vfs_read.part.1+0x6c/0x123
>   handle_mm_fault+0x831/0xf9b
>   __fget+0x7e/0xbf
>   SyS_read+0x4d/0xb5
> 
> ceph_read_iter() uses current->journal_info to pass context info to
> ceph_readpages(). Because ceph_readpages() needs to know if its caller
> has already gotten capability of using page cache (distinguish read
> from readahead/fadvise). ceph_read_iter() set current->journal_info,
> then calls generic_file_read_iter().
> 
> In above Oops, page fault happened when copying data to userspace.
> Page fault handler called ext4_page_mkwrite(). Ext4 code read
> current->journal_info and assumed it is journal handle.
> 
> I checked other filesystems, btrfs probably suffers similar problem
> for its readpage. (page fault happens when write() copies data from
> userspace memory and the memory is mapped to a file in btrfs.
> verify_parent_transid() can be called during readpage)
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: "Yan, Zheng" <zyan@redhat.com>

I am not an FS expert so (ab)using journal_info for unrelated purposes
might be acceptable in general but hooking into the generic PF path like
this is just too ugly to live. Can this be limited to a FS code so that
not everybody has to pay additional cycles? With a big fat warning that
(ab)users might want to find a better way to comunicate their internal
stuff.

> ---
>  mm/memory.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index a728bed16c20..db2a50233c49 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4044,6 +4044,7 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		unsigned int flags)
>  {
>  	int ret;
> +	void *old_journal_info;
>  
>  	__set_current_state(TASK_RUNNING);
>  
> @@ -4065,11 +4066,24 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  	if (flags & FAULT_FLAG_USER)
>  		mem_cgroup_oom_enable();
>  
> +	/*
> +	 * Fault can happen when filesystem A's read_iter()/write_iter()
> +	 * copies data to/from userspace. Filesystem A may have set
> +	 * current->journal_info. If the userspace memory is MAP_SHARED
> +	 * mapped to a file in filesystem B, we later may call filesystem
> +	 * B's vm operation. Filesystem B may also want to read/set
> +	 * current->journal_info.
> +	 */
> +	old_journal_info = current->journal_info;
> +	current->journal_info = NULL;
> +
>  	if (unlikely(is_vm_hugetlb_page(vma)))
>  		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
>  	else
>  		ret = __handle_mm_fault(vma, address, flags);
>  
> +	current->journal_info = old_journal_info;
> +
>  	if (flags & FAULT_FLAG_USER) {
>  		mem_cgroup_oom_disable();
>  		/*
> -- 
> 2.13.6
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm: save/restore current->journal_info in handle_mm_fault

[Jan Kara]

On Thu 14-12-17 18:55:27, Yan, Zheng wrote:
> We recently got an Oops report:
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: jbd2__journal_start+0x38/0x1a2
> [...]
> Call Trace:
>   ext4_page_mkwrite+0x307/0x52b
>   _ext4_get_block+0xd8/0xd8
>   do_page_mkwrite+0x6e/0xd8
>   handle_mm_fault+0x686/0xf9b
>   mntput_no_expire+0x1f/0x21e
>   __do_page_fault+0x21d/0x465
>   dput+0x4a/0x2f7
>   page_fault+0x22/0x30
>   copy_user_generic_string+0x2c/0x40
>   copy_page_to_iter+0x8c/0x2b8
>   generic_file_read_iter+0x26e/0x845
>   timerqueue_del+0x31/0x90
>   ceph_read_iter+0x697/0xa33 [ceph]
>   hrtimer_cancel+0x23/0x41
>   futex_wait+0x1c8/0x24d
>   get_futex_key+0x32c/0x39a
>   __vfs_read+0xe0/0x130
>   vfs_read.part.1+0x6c/0x123
>   handle_mm_fault+0x831/0xf9b
>   __fget+0x7e/0xbf
>   SyS_read+0x4d/0xb5
> 
> ceph_read_iter() uses current->journal_info to pass context info to
> ceph_readpages(). Because ceph_readpages() needs to know if its caller
> has already gotten capability of using page cache (distinguish read
> from readahead/fadvise). ceph_read_iter() set current->journal_info,
> then calls generic_file_read_iter().
> 
> In above Oops, page fault happened when copying data to userspace.
> Page fault handler called ext4_page_mkwrite(). Ext4 code read
> current->journal_info and assumed it is journal handle.
> 
> I checked other filesystems, btrfs probably suffers similar problem
> for its readpage. (page fault happens when write() copies data from
> userspace memory and the memory is mapped to a file in btrfs.
> verify_parent_transid() can be called during readpage)
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: "Yan, Zheng" <zyan@redhat.com>

I agree with the analysis but the patch is too ugly too live. Ceph just
should not be abusing current->journal_info for passing information between
two random functions or when it does a hackery like this, it should just
make sure the pieces hold together. Poluting generic code to accommodate
this hack in Ceph is not acceptable. Also bear in mind there are likely
other code paths (e.g. memory reclaim) which could recurse into another
filesystem confusing it with non-NULL current->journal_info in the same
way.

In this particular case I'm not sure why does ceph pass 'filp' into
readpage() / readpages() handler when it already gets that pointer as part
of arguments...

								Honza

> diff --git a/mm/memory.c b/mm/memory.c
> index a728bed16c20..db2a50233c49 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4044,6 +4044,7 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  		unsigned int flags)
>  {
>  	int ret;
> +	void *old_journal_info;
>  
>  	__set_current_state(TASK_RUNNING);
>  
> @@ -4065,11 +4066,24 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>  	if (flags & FAULT_FLAG_USER)
>  		mem_cgroup_oom_enable();
>  
> +	/*
> +	 * Fault can happen when filesystem A's read_iter()/write_iter()
> +	 * copies data to/from userspace. Filesystem A may have set
> +	 * current->journal_info. If the userspace memory is MAP_SHARED
> +	 * mapped to a file in filesystem B, we later may call filesystem
> +	 * B's vm operation. Filesystem B may also want to read/set
> +	 * current->journal_info.
> +	 */
> +	old_journal_info = current->journal_info;
> +	current->journal_info = NULL;
> +
>  	if (unlikely(is_vm_hugetlb_page(vma)))
>  		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
>  	else
>  		ret = __handle_mm_fault(vma, address, flags);
>  
> +	current->journal_info = old_journal_info;
> +
>  	if (flags & FAULT_FLAG_USER) {
>  		mem_cgroup_oom_disable();
>  		/*
> -- 
> 2.13.6
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] mm: save/restore current->journal_info in handle_mm_fault

[Yan, Zheng]

On Thu, Dec 14, 2017 at 9:43 PM, Jan Kara <jack@suse.cz> wrote:
> On Thu 14-12-17 18:55:27, Yan, Zheng wrote:
>> We recently got an Oops report:
>>
>> BUG: unable to handle kernel NULL pointer dereference at (null)
>> IP: jbd2__journal_start+0x38/0x1a2
>> [...]
>> Call Trace:
>>   ext4_page_mkwrite+0x307/0x52b
>>   _ext4_get_block+0xd8/0xd8
>>   do_page_mkwrite+0x6e/0xd8
>>   handle_mm_fault+0x686/0xf9b
>>   mntput_no_expire+0x1f/0x21e
>>   __do_page_fault+0x21d/0x465
>>   dput+0x4a/0x2f7
>>   page_fault+0x22/0x30
>>   copy_user_generic_string+0x2c/0x40
>>   copy_page_to_iter+0x8c/0x2b8
>>   generic_file_read_iter+0x26e/0x845
>>   timerqueue_del+0x31/0x90
>>   ceph_read_iter+0x697/0xa33 [ceph]
>>   hrtimer_cancel+0x23/0x41
>>   futex_wait+0x1c8/0x24d
>>   get_futex_key+0x32c/0x39a
>>   __vfs_read+0xe0/0x130
>>   vfs_read.part.1+0x6c/0x123
>>   handle_mm_fault+0x831/0xf9b
>>   __fget+0x7e/0xbf
>>   SyS_read+0x4d/0xb5
>>
>> ceph_read_iter() uses current->journal_info to pass context info to
>> ceph_readpages(). Because ceph_readpages() needs to know if its caller
>> has already gotten capability of using page cache (distinguish read
>> from readahead/fadvise). ceph_read_iter() set current->journal_info,
>> then calls generic_file_read_iter().
>>
>> In above Oops, page fault happened when copying data to userspace.
>> Page fault handler called ext4_page_mkwrite(). Ext4 code read
>> current->journal_info and assumed it is journal handle.
>>
>> I checked other filesystems, btrfs probably suffers similar problem
>> for its readpage. (page fault happens when write() copies data from
>> userspace memory and the memory is mapped to a file in btrfs.
>> verify_parent_transid() can be called during readpage)
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
>
> I agree with the analysis but the patch is too ugly too live. Ceph just
> should not be abusing current->journal_info for passing information between
> two random functions or when it does a hackery like this, it should just
> make sure the pieces hold together. Poluting generic code to accommodate
> this hack in Ceph is not acceptable. Also bear in mind there are likely
> other code paths (e.g. memory reclaim) which could recurse into another
> filesystem confusing it with non-NULL current->journal_info in the same
> way.

But ...

some filesystem set journal_info in its write_begin(), then clear it
in write_end(). If buffer for write is mapped to another filesystem,
current->journal can leak to the later filesystem's page_readpage().
The later filesystem may read current->journal and treat it as its own
journal handle.  Besides, most filesystem's vm fault handle is
filemap_fault(), filemap also may tigger memory reclaim.

>
> In this particular case I'm not sure why does ceph pass 'filp' into
> readpage() / readpages() handler when it already gets that pointer as part
> of arguments...

It actually a flag which tells ceph_readpages() if its caller is
ceph_read_iter or readahead/fadvise/madvise. because when there are
multiple clients read/write a file a the same time, page cache should
be disabled.

Regards
Yan, Zheng

>
>                                                                 Honza
>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index a728bed16c20..db2a50233c49 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4044,6 +4044,7 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>               unsigned int flags)
>>  {
>>       int ret;
>> +     void *old_journal_info;
>>
>>       __set_current_state(TASK_RUNNING);
>>
>> @@ -4065,11 +4066,24 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>>       if (flags & FAULT_FLAG_USER)
>>               mem_cgroup_oom_enable();
>>
>> +     /*
>> +      * Fault can happen when filesystem A's read_iter()/write_iter()
>> +      * copies data to/from userspace. Filesystem A may have set
>> +      * current->journal_info. If the userspace memory is MAP_SHARED
>> +      * mapped to a file in filesystem B, we later may call filesystem
>> +      * B's vm operation. Filesystem B may also want to read/set
>> +      * current->journal_info.
>> +      */
>> +     old_journal_info = current->journal_info;
>> +     current->journal_info = NULL;
>> +
>>       if (unlikely(is_vm_hugetlb_page(vma)))
>>               ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
>>       else
>>               ret = __handle_mm_fault(vma, address, flags);
>>
>> +     current->journal_info = old_journal_info;
>> +
>>       if (flags & FAULT_FLAG_USER) {
>>               mem_cgroup_oom_disable();
>>               /*
>> --
>> 2.13.6
>>
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
> --
> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html