fanotify: Make sure to check event_len when copying
diff mbox series

Message ID 20181204234446.GA4676@beast
State New
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Series
  • fanotify: Make sure to check event_len when copying
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Commit Message

Kees Cook Dec. 4, 2018, 11:44 p.m. UTC
As a precaution, make sure we check event_len when copying to userspace.
Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Comments

Amir Goldstein Dec. 5, 2018, 7:15 a.m. UTC | #1
On Wed, Dec 5, 2018 at 1:44 AM Kees Cook <keescook@chromium.org> wrote:
>
> As a precaution, make sure we check event_len when copying to userspace.
> Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de
>

This precaution serves the new fanotify_event_info_fid format well:
https://marc.info/?l=linux-fsdevel&m=154375073318106&w=2
but also conflicts with my series.

I can weave your patch into my series and add a similar sanity check in
copy_fid_to_user() or if Jan applies your patch and has more comments
on my v4 series, I'll rebase on top of that.

Thanks,
Amir.

> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index e03be5071362..d9484a0ac6b3 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,
>
>  static ssize_t copy_event_to_user(struct fsnotify_group *group,
>                                   struct fsnotify_event *event,
> -                                 char __user *buf)
> +                                 char __user *buf, size_t count)
>  {
>         struct fanotify_event_metadata fanotify_event_metadata;
>         struct file *f;
> @@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
>
>         fd = fanotify_event_metadata.fd;
>         ret = -EFAULT;
> +       /*
> +        * Sanity check copy size in case get_one_event() and
> +        * fill_event_metadata() event_len sizes ever get out of sync.
> +        */
> +       if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
> +               goto out_close_fd;
>         if (copy_to_user(buf, &fanotify_event_metadata,
>                          fanotify_event_metadata.event_len))
>                 goto out_close_fd;
> @@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
>                         continue;
>                 }
>
> -               ret = copy_event_to_user(group, kevent, buf);
> +               ret = copy_event_to_user(group, kevent, buf, count);
>                 if (unlikely(ret == -EOPENSTALE)) {
>                         /*
>                          * We cannot report events with stale fd so drop it.
> --
> 2.17.1
>
>
> --
> Kees Cook
Jan Kara Dec. 5, 2018, 12:09 p.m. UTC | #2
On Tue 04-12-18 15:44:46, Kees Cook wrote:
> As a precaution, make sure we check event_len when copying to userspace.
> Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for the patch, I've added it to my tree.

								Honza

> ---
>  fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index e03be5071362..d9484a0ac6b3 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,
>  
>  static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  				  struct fsnotify_event *event,
> -				  char __user *buf)
> +				  char __user *buf, size_t count)
>  {
>  	struct fanotify_event_metadata fanotify_event_metadata;
>  	struct file *f;
> @@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  
>  	fd = fanotify_event_metadata.fd;
>  	ret = -EFAULT;
> +	/*
> +	 * Sanity check copy size in case get_one_event() and
> +	 * fill_event_metadata() event_len sizes ever get out of sync.
> +	 */
> +	if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
> +		goto out_close_fd;
>  	if (copy_to_user(buf, &fanotify_event_metadata,
>  			 fanotify_event_metadata.event_len))
>  		goto out_close_fd;
> @@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
>  			continue;
>  		}
>  
> -		ret = copy_event_to_user(group, kevent, buf);
> +		ret = copy_event_to_user(group, kevent, buf, count);
>  		if (unlikely(ret == -EOPENSTALE)) {
>  			/*
>  			 * We cannot report events with stale fd so drop it.
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook
Jan Kara Dec. 5, 2018, 12:10 p.m. UTC | #3
On Wed 05-12-18 09:15:44, Amir Goldstein wrote:
> On Wed, Dec 5, 2018 at 1:44 AM Kees Cook <keescook@chromium.org> wrote:
> >
> > As a precaution, make sure we check event_len when copying to userspace.
> > Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de
> >
> 
> This precaution serves the new fanotify_event_info_fid format well:
> https://marc.info/?l=linux-fsdevel&m=154375073318106&w=2
> but also conflicts with my series.
> 
> I can weave your patch into my series and add a similar sanity check in
> copy_fid_to_user() or if Jan applies your patch and has more comments
> on my v4 series, I'll rebase on top of that.

Yeah, I don't think there's any need for you to rebase just now. Either
I'll fixup your patch or you'll do the rebase if there are further changes
to the series...

								Honza

> 
> Thanks,
> Amir.
> 
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> > index e03be5071362..d9484a0ac6b3 100644
> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,
> >
> >  static ssize_t copy_event_to_user(struct fsnotify_group *group,
> >                                   struct fsnotify_event *event,
> > -                                 char __user *buf)
> > +                                 char __user *buf, size_t count)
> >  {
> >         struct fanotify_event_metadata fanotify_event_metadata;
> >         struct file *f;
> > @@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
> >
> >         fd = fanotify_event_metadata.fd;
> >         ret = -EFAULT;
> > +       /*
> > +        * Sanity check copy size in case get_one_event() and
> > +        * fill_event_metadata() event_len sizes ever get out of sync.
> > +        */
> > +       if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
> > +               goto out_close_fd;
> >         if (copy_to_user(buf, &fanotify_event_metadata,
> >                          fanotify_event_metadata.event_len))
> >                 goto out_close_fd;
> > @@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
> >                         continue;
> >                 }
> >
> > -               ret = copy_event_to_user(group, kevent, buf);
> > +               ret = copy_event_to_user(group, kevent, buf, count);
> >                 if (unlikely(ret == -EOPENSTALE)) {
> >                         /*
> >                          * We cannot report events with stale fd so drop it.
> > --
> > 2.17.1
> >
> >
> > --
> > Kees Cook

Patch
diff mbox series

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index e03be5071362..d9484a0ac6b3 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -206,7 +206,7 @@  static int process_access_response(struct fsnotify_group *group,
 
 static ssize_t copy_event_to_user(struct fsnotify_group *group,
 				  struct fsnotify_event *event,
-				  char __user *buf)
+				  char __user *buf, size_t count)
 {
 	struct fanotify_event_metadata fanotify_event_metadata;
 	struct file *f;
@@ -220,6 +220,12 @@  static ssize_t copy_event_to_user(struct fsnotify_group *group,
 
 	fd = fanotify_event_metadata.fd;
 	ret = -EFAULT;
+	/*
+	 * Sanity check copy size in case get_one_event() and
+	 * fill_event_metadata() event_len sizes ever get out of sync.
+	 */
+	if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
+		goto out_close_fd;
 	if (copy_to_user(buf, &fanotify_event_metadata,
 			 fanotify_event_metadata.event_len))
 		goto out_close_fd;
@@ -295,7 +301,7 @@  static ssize_t fanotify_read(struct file *file, char __user *buf,
 			continue;
 		}
 
-		ret = copy_event_to_user(group, kevent, buf);
+		ret = copy_event_to_user(group, kevent, buf, count);
 		if (unlikely(ret == -EOPENSTALE)) {
 			/*
 			 * We cannot report events with stale fd so drop it.