diff mbox series

[15/18] vfs, fdtable: prevent bounds-check bypass via speculative execution

Message ID 151520107515.32271.4902355030043648595.stgit@dwillia2-desk3.amr.corp.intel.com
State Not Applicable, archived
Delegated to: David Miller
Headers show
Series prevent bounds-check bypass via speculative execution | expand

Commit Message

Dan Williams Jan. 6, 2018, 1:11 a.m. UTC 
Expectedly, static analysis reports that 'fd' is a user controlled value
that is used as a data dependency to read from the 'fdt->fd' array.  In
order to avoid potential leaks of kernel memory values, block
speculative execution of the instruction stream that could issue reads
based on an invalid 'file *' returned from __fcheck_files.

Based on an original patch by Elena Reshetova.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/fdtable.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Sergei Shtylyov Jan. 6, 2018, 10:05 a.m. UTC | #1 
On 1/6/2018 4:11 AM, Dan Williams wrote:

> Expectedly, static analysis reports that 'fd' is a user controlled value
> that is used as a data dependency to read from the 'fdt->fd' array.  In
> order to avoid potential leaks of kernel memory values, block
> speculative execution of the instruction stream that could issue reads
> based on an invalid 'file *' returned from __fcheck_files.
> 
> Based on an original patch by Elena Reshetova.
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>   include/linux/fdtable.h |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
> index 1c65817673db..4a147c5c2533 100644
> --- a/include/linux/fdtable.h
> +++ b/include/linux/fdtable.h
> @@ -81,9 +81,10 @@ struct dentry;
>   static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd)
>   {
>   	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
> +	struct file __rcu **fdp;
>   
> -	if (fd < fdt->max_fds)
> -		return rcu_dereference_raw(fdt->fd[fd]);
> +	if ((fdp = nospec_array_ptr(fdt->fd, fd, fdt->max_fds)))

    And here...

> +		return rcu_dereference_raw(*fdp);
>   	return NULL;
>   }
>   

MMR, Sergei
diff mbox series

Patch

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 1c65817673db..4a147c5c2533 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -81,9 +81,10 @@  struct dentry;
 static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd)
 {
 	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
+	struct file __rcu **fdp;
 
-	if (fd < fdt->max_fds)
-		return rcu_dereference_raw(fdt->fd[fd]);
+	if ((fdp = nospec_array_ptr(fdt->fd, fd, fdt->max_fds)))
+		return rcu_dereference_raw(*fdp);
 	return NULL;
 }