exec: Implement kernel_execve
To allow the kernel not to play games with set_fs to call exec
implement kernel_execve. The function kernel_execve takes pointers
into kernel memory and copies the values pointed to onto the new
userspace stack.
The calls with arguments from kernel space of do_execve are replaced
with calls to kernel_execve.
The calls do_execve and do_execveat are made static as there are now
no callers outside of exec.
The comments that mention do_execve are updated to refer to
kernel_execve or execve depending on the circumstances. In addition
to correcting the comments, this makes it easy to grep for do_execve
and verify it is not used.
Inspired-by: https://lkml.kernel.org/r/20200627072704.2447163-1-hch@lst.de
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87wo365ikj.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/exec.c b/fs/exec.c
index f8135dc..3698252 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -448,6 +448,23 @@ static int count(struct user_arg_ptr argv, int max)
return i;
}
+static int count_strings_kernel(const char *const *argv)
+{
+ int i;
+
+ if (!argv)
+ return 0;
+
+ for (i = 0; argv[i]; ++i) {
+ if (i >= MAX_ARG_STRINGS)
+ return -E2BIG;
+ if (fatal_signal_pending(current))
+ return -ERESTARTNOHAND;
+ cond_resched();
+ }
+ return i;
+}
+
static int bprm_stack_limits(struct linux_binprm *bprm)
{
unsigned long limit, ptr_size;
@@ -624,6 +641,20 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
}
EXPORT_SYMBOL(copy_string_kernel);
+static int copy_strings_kernel(int argc, const char *const *argv,
+ struct linux_binprm *bprm)
+{
+ while (argc-- > 0) {
+ int ret = copy_string_kernel(argv[argc], bprm);
+ if (ret < 0)
+ return ret;
+ if (fatal_signal_pending(current))
+ return -ERESTARTNOHAND;
+ cond_resched();
+ }
+ return 0;
+}
+
#ifdef CONFIG_MMU
/*
@@ -1991,7 +2022,60 @@ static int do_execveat_common(int fd, struct filename *filename,
return retval;
}
-int do_execve(struct filename *filename,
+int kernel_execve(const char *kernel_filename,
+ const char *const *argv, const char *const *envp)
+{
+ struct filename *filename;
+ struct linux_binprm *bprm;
+ int fd = AT_FDCWD;
+ int retval;
+
+ filename = getname_kernel(kernel_filename);
+ if (IS_ERR(filename))
+ return PTR_ERR(filename);
+
+ bprm = alloc_bprm(fd, filename);
+ if (IS_ERR(bprm)) {
+ retval = PTR_ERR(bprm);
+ goto out_ret;
+ }
+
+ retval = count_strings_kernel(argv);
+ if (retval < 0)
+ goto out_free;
+ bprm->argc = retval;
+
+ retval = count_strings_kernel(envp);
+ if (retval < 0)
+ goto out_free;
+ bprm->envc = retval;
+
+ retval = bprm_stack_limits(bprm);
+ if (retval < 0)
+ goto out_free;
+
+ retval = copy_string_kernel(bprm->filename, bprm);
+ if (retval < 0)
+ goto out_free;
+ bprm->exec = bprm->p;
+
+ retval = copy_strings_kernel(bprm->envc, envp, bprm);
+ if (retval < 0)
+ goto out_free;
+
+ retval = copy_strings_kernel(bprm->argc, argv, bprm);
+ if (retval < 0)
+ goto out_free;
+
+ retval = bprm_execve(bprm, fd, filename, 0);
+out_free:
+ free_bprm(bprm);
+out_ret:
+ putname(filename);
+ return retval;
+}
+
+static int do_execve(struct filename *filename,
const char __user *const __user *__argv,
const char __user *const __user *__envp)
{
@@ -2000,7 +2084,7 @@ int do_execve(struct filename *filename,
return do_execveat_common(AT_FDCWD, filename, argv, envp, 0);
}
-int do_execveat(int fd, struct filename *filename,
+static int do_execveat(int fd, struct filename *filename,
const char __user *const __user *__argv,
const char __user *const __user *__envp,
int flags)