[PATCH v3 9/9] vfs, fdtable: prevent bounds-check bypass via speculative execution

[Dan Williams]

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.

Cc: Al Viro 
Co-developed-by: Elena Reshetova 
Signed-off-by: Dan Williams 
---
 include/linux/fdtable.h |7 +--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 1c65817673db..9731f1a255db 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -10,6 +10,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -81,9 +82,11 @@ 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]);
+   fdp = array_ptr(fdt->fd, fd, fdt->max_fds);
+   if (fdp)
+   return rcu_dereference_raw(*fdp);
return NULL;
 }
 

[PATCH v3 9/9] vfs, fdtable: prevent bounds-check bypass via speculative execution

[Dan Williams]

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.

Cc: Al Viro 
Co-developed-by: Elena Reshetova 
Signed-off-by: Dan Williams 
---
 include/linux/fdtable.h |7 +--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 1c65817673db..9731f1a255db 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -10,6 +10,7 @@
 #include 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 
@@ -81,9 +82,11 @@ 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]);
+   fdp = array_ptr(fdt->fd, fd, fdt->max_fds);
+   if (fdp)
+   return rcu_dereference_raw(*fdp);
return NULL;
 }