The 'struct fdtable' holds the file descriptor table information, including the current file descriptor array 'fd' and its size 'max_fds'. To harden the kernel against out-of-bounds accesses, we can annotate the 'fd' pointer field with the '__counted_by_ptr' attribute, referencing 'max_fds'.
The compiler uses the '__counted_by_ptr' attribute to track the size of the memory allocated for the pointer field, enabling runtime bounds checks under KASAN and fortified functions. There are three places where a 'struct fdtable' is initialized, and in all of them, 'max_fds' is set before the 'fd' pointer is accessed or assigned in all allocation and initialization places. No accesses to 'fd' occur before 'max_fds' is set, preventing any potential runtime false-positives or panics due to uninitialized count fields. This patch was generated by CodeMender and checked by submitter. Cc: [email protected] Signed-off-by: Bill Wendling <[email protected]> --- Cc: Alexander Viro <[email protected]> Cc: Christian Brauner <[email protected]> Cc: Jan Kara <[email protected]> Cc: Kees Cook <[email protected]> Cc: "Gustavo A. R. Silva" <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] --- include/linux/fdtable.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h index c45306a9f007..3a5c88291125 100644 --- a/include/linux/fdtable.h +++ b/include/linux/fdtable.h @@ -25,7 +25,7 @@ struct fdtable { unsigned int max_fds; - struct file __rcu **fd; /* current fd array */ + struct file __rcu **fd __counted_by_ptr(max_fds); /* current fd array */ unsigned long *close_on_exec; unsigned long *open_fds; unsigned long *full_fds_bits; -- 2.55.0.679.g6767b8d81c-goog
