When filtering xattr list for reading, presence of trusted xattr
results in a security audit log. However, if there is other content
no errno will be set, and if there isn't, the errno will be -ENODATA
and not -EPERM as is usually associated with a lack of capability.
The check does not block the request to list the xattrs present.
Switch to has_capability_noaudit to reflect a more appropriate check.
Signed-off-by: Mark Salyzyn <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: [email protected] # v3.18
Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
---
Replaced ns_capable_noaudit with 3.18.y tree specific
has_capability_noaudit present in original submission to kernel.org
commit 5c2e9f346b815841f9bed6029ebcb06415caf640
("ovl: filter of trusted xattr results in audit")
fs/overlayfs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index a01ec1836a72..1175efa5e956 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
return true;
/* Never list trusted.overlay, list other trusted for superuser only */
- return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
+ return !ovl_is_private_xattr(s) &&
+ has_capability_noaudit(current, CAP_SYS_ADMIN);
}
ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
--
2.23.0.581.g78d2f28ef7-goog
On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
> When filtering xattr list for reading, presence of trusted xattr
> results in a security audit log. However, if there is other content
> no errno will be set, and if there isn't, the errno will be -ENODATA
> and not -EPERM as is usually associated with a lack of capability.
> The check does not block the request to list the xattrs present.
>
> Switch to has_capability_noaudit to reflect a more appropriate check.
>
> Signed-off-by: Mark Salyzyn <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: [email protected] # v3.18
> Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
> Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
> ---
> Replaced ns_capable_noaudit with 3.18.y tree specific
> has_capability_noaudit present in original submission to kernel.org
> commit 5c2e9f346b815841f9bed6029ebcb06415caf640
> ("ovl: filter of trusted xattr results in audit")
>
> fs/overlayfs/inode.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index a01ec1836a72..1175efa5e956 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
> return true;
>
> /* Never list trusted.overlay, list other trusted for superuser only */
> - return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
> + return !ovl_is_private_xattr(s) &&
> + has_capability_noaudit(current, CAP_SYS_ADMIN);
> }
>
> ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
> --
> 2.23.0.581.g78d2f28ef7-goog
>
Thanks for the backport, this one worked!
greg k-h
On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
> > When filtering xattr list for reading, presence of trusted xattr
> > results in a security audit log. However, if there is other content
> > no errno will be set, and if there isn't, the errno will be -ENODATA
> > and not -EPERM as is usually associated with a lack of capability.
> > The check does not block the request to list the xattrs present.
> >
> > Switch to has_capability_noaudit to reflect a more appropriate check.
> >
> > Signed-off-by: Mark Salyzyn <[email protected]>
> > Cc: [email protected]
> > Cc: [email protected]
> > Cc: Greg Kroah-Hartman <[email protected]>
> > Cc: [email protected] # v3.18
> > Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
> > Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
> > ---
> > Replaced ns_capable_noaudit with 3.18.y tree specific
> > has_capability_noaudit present in original submission to kernel.org
> > commit 5c2e9f346b815841f9bed6029ebcb06415caf640
> > ("ovl: filter of trusted xattr results in audit")
> >
> > fs/overlayfs/inode.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> > index a01ec1836a72..1175efa5e956 100644
> > --- a/fs/overlayfs/inode.c
> > +++ b/fs/overlayfs/inode.c
> > @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
> > return true;
> >
> > /* Never list trusted.overlay, list other trusted for superuser only */
> > - return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
> > + return !ovl_is_private_xattr(s) &&
> > + has_capability_noaudit(current, CAP_SYS_ADMIN);
> > }
> >
> > ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
> > --
> > 2.23.0.581.g78d2f28ef7-goog
> >
>
> Thanks for the backport, this one worked!
I spoke too soon:
ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
That function isn't exported for modules :(
greg k-h
On 10/7/19 9:17 AM, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
>> On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
>>> When filtering xattr list for reading, presence of trusted xattr
>>> results in a security audit log. However, if there is other content
>>> no errno will be set, and if there isn't, the errno will be -ENODATA
>>> and not -EPERM as is usually associated with a lack of capability.
>>> The check does not block the request to list the xattrs present.
>>>
>>> Switch to has_capability_noaudit to reflect a more appropriate check.
>>>
>>> Signed-off-by: Mark Salyzyn <[email protected]>
>>> Cc: [email protected]
>>> Cc: [email protected]
>>> Cc: Greg Kroah-Hartman <[email protected]>
>>> Cc: [email protected] # v3.18
>>> Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
>>> Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
>>> ---
>>> Replaced ns_capable_noaudit with 3.18.y tree specific
>>> has_capability_noaudit present in original submission to kernel.org
>>> commit 5c2e9f346b815841f9bed6029ebcb06415caf640
>>> ("ovl: filter of trusted xattr results in audit")
>>>
>>> fs/overlayfs/inode.c | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>> index a01ec1836a72..1175efa5e956 100644
>>> --- a/fs/overlayfs/inode.c
>>> +++ b/fs/overlayfs/inode.c
>>> @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
>>> return true;
>>>
>>> /* Never list trusted.overlay, list other trusted for superuser only */
>>> - return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
>>> + return !ovl_is_private_xattr(s) &&
>>> + has_capability_noaudit(current, CAP_SYS_ADMIN);
>>> }
>>>
>>> ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
>>> --
>>> 2.23.0.581.g78d2f28ef7-goog
>>>
>> Thanks for the backport, this one worked!
> I spoke too soon:
>
> ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
>
> That function isn't exported for modules :(
>
> greg k-h
<sigh>
Now what is the playbook, we have three options in order of preference:
1) #ifdef MODULE use capable() to preserve API, add a short comment
about the side effects if overlayfs is used as a module.
2) export has_capability_nodaudit (proc and oom_kill use it, and are
both built-in only), but affect the 3.18 API at near EOL. AFAIK no one
wants that?
3) Do nothing more. Make this a distro concern only. Leave this posted
as a back-port for the record, but never merged, for those that are
_interested_ and declare 3.18 stable as noisy for sepolicy and overlayfs
under some usage patterns with few user space mitigation unless they
explicitly take this back-port into their tree (eg: android common
kernel) if used built-in. This way, in 3.18.y at least the module and
built-in version behave the _same_ in stable.
Looking for feedback.
Sincerely -- Mark Salyzyn
On Mon, Oct 07, 2019 at 06:17:25PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
> > On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
> > > When filtering xattr list for reading, presence of trusted xattr
> > > results in a security audit log. However, if there is other content
> > > no errno will be set, and if there isn't, the errno will be -ENODATA
> > > and not -EPERM as is usually associated with a lack of capability.
> > > The check does not block the request to list the xattrs present.
> > >
> > > Switch to has_capability_noaudit to reflect a more appropriate check.
> > >
> > > Signed-off-by: Mark Salyzyn <[email protected]>
> > > Cc: [email protected]
> > > Cc: [email protected]
> > > Cc: Greg Kroah-Hartman <[email protected]>
> > > Cc: [email protected] # v3.18
> > > Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
> > > Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
> > > ---
> > > Replaced ns_capable_noaudit with 3.18.y tree specific
> > > has_capability_noaudit present in original submission to kernel.org
> > > commit 5c2e9f346b815841f9bed6029ebcb06415caf640
> > > ("ovl: filter of trusted xattr results in audit")
> > >
> > > fs/overlayfs/inode.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> > > index a01ec1836a72..1175efa5e956 100644
> > > --- a/fs/overlayfs/inode.c
> > > +++ b/fs/overlayfs/inode.c
> > > @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
> > > return true;
> > >
> > > /* Never list trusted.overlay, list other trusted for superuser only */
> > > - return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
> > > + return !ovl_is_private_xattr(s) &&
> > > + has_capability_noaudit(current, CAP_SYS_ADMIN);
> > > }
> > >
> > > ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
> > > --
> > > 2.23.0.581.g78d2f28ef7-goog
> > >
> >
> > Thanks for the backport, this one worked!
>
> I spoke too soon:
>
> ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
>
> That function isn't exported for modules :(
But, if this really is needed, and it fixes the issue, I'll go export
that symbol with EXPORT_SYMBOL_GPL() to fix the problem. Any
objections?
thanks,
greg k-h
On 10/7/19 9:40 AM, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 06:17:25PM +0200, Greg Kroah-Hartman wrote:
>> On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
>>> On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
>>>> When filtering xattr list for reading, presence of trusted xattr
>>>> results in a security audit log. However, if there is other content
>>>> no errno will be set, and if there isn't, the errno will be -ENODATA
>>>> and not -EPERM as is usually associated with a lack of capability.
>>>> The check does not block the request to list the xattrs present.
>>>>
>>>> Switch to has_capability_noaudit to reflect a more appropriate check.
>>>>
>>>> Signed-off-by: Mark Salyzyn <[email protected]>
>>>> Cc: [email protected]
>>>> Cc: [email protected]
>>>> Cc: Greg Kroah-Hartman <[email protected]>
>>>> Cc: [email protected] # v3.18
>>>> Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
>>>> Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
>>>> ---
>>>> Replaced ns_capable_noaudit with 3.18.y tree specific
>>>> has_capability_noaudit present in original submission to kernel.org
>>>> commit 5c2e9f346b815841f9bed6029ebcb06415caf640
>>>> ("ovl: filter of trusted xattr results in audit")
>>>>
>>>> fs/overlayfs/inode.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>>> index a01ec1836a72..1175efa5e956 100644
>>>> --- a/fs/overlayfs/inode.c
>>>> +++ b/fs/overlayfs/inode.c
>>>> @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
>>>> return true;
>>>>
>>>> /* Never list trusted.overlay, list other trusted for superuser only */
>>>> - return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
>>>> + return !ovl_is_private_xattr(s) &&
>>>> + has_capability_noaudit(current, CAP_SYS_ADMIN);
>>>> }
>>>>
>>>> ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
>>>> --
>>>> 2.23.0.581.g78d2f28ef7-goog
>>>>
>>> Thanks for the backport, this one worked!
>> I spoke too soon:
>>
>> ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
>>
>> That function isn't exported for modules :(
> But, if this really is needed, and it fixes the issue, I'll go export
> that symbol with EXPORT_SYMBOL_GPL() to fix the problem. Any
> objections?
>
> thanks,
>
> greg k-h
Ok, you just answered my question in cross-emails. Yes,
EXPORT_SYMBOL_GPL() (my option 2).
Thanks
-- Mark Salyzyn
On Mon, Oct 07, 2019 at 09:42:08AM -0700, Mark Salyzyn wrote:
>
> <sigh>
>
> Now what is the playbook, we have three options in order of preference:
>
> 1) #ifdef MODULE use capable() to preserve API, add a short comment about
> the side effects if overlayfs is used as a module.
>
> 2) export has_capability_nodaudit (proc and oom_kill use it, and are both
> built-in only), but affect the 3.18 API at near EOL. AFAIK no one wants
> that?
I'll just do this. 3.18 is EOL, this is only being done for a
distro-specific tree (i.e. AOSP).
> 3) Do nothing more. Make this a distro concern only. Leave this posted as a
> back-port for the record, but never merged, for those that are _interested_
> and declare 3.18 stable as noisy for sepolicy and overlayfs under some usage
> patterns with few user space mitigation unless they explicitly take this
> back-port into their tree (eg: android common kernel) if used built-in. This
> way, in 3.18.y at least the module and built-in version behave the _same_ in
> stable.
I'll just add the export to the patch and check this into AOSP, thanks!
greg k-h