vfs: define a generic function to read a file from the kernel
For a while it was looked down upon to directly read files from Linux.
These days there exists a few mechanisms in the kernel that do just
this though to load a file into a local buffer. There are minor but
important checks differences on each. This patch set is the first
attempt at resolving some of these differences.
This patch introduces a common function for reading files from the kernel
with the corresponding security post-read hook and function.
Changelog v4+:
- export security_kernel_post_read_file() - Fengguang Wu
v3:
- additional bounds checking - Luis
v2:
- To simplify patch review, re-ordered patches
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: Luis R. Rodriguez <mcgrof@suse.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/exec.c b/fs/exec.c
index dcd4ac7..6b6668b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -56,6 +56,7 @@
#include <linux/pipe_fs_i.h>
#include <linux/oom.h>
#include <linux/compat.h>
+#include <linux/vmalloc.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
@@ -831,6 +832,58 @@
EXPORT_SYMBOL(kernel_read);
+int kernel_read_file(struct file *file, void **buf, loff_t *size,
+ loff_t max_size)
+{
+ loff_t i_size, pos;
+ ssize_t bytes = 0;
+ int ret;
+
+ if (!S_ISREG(file_inode(file)->i_mode) || max_size < 0)
+ return -EINVAL;
+
+ i_size = i_size_read(file_inode(file));
+ if (max_size > 0 && i_size > max_size)
+ return -EFBIG;
+ if (i_size <= 0)
+ return -EINVAL;
+
+ *buf = vmalloc(i_size);
+ if (!*buf)
+ return -ENOMEM;
+
+ pos = 0;
+ while (pos < i_size) {
+ bytes = kernel_read(file, pos, (char *)(*buf) + pos,
+ i_size - pos);
+ if (bytes < 0) {
+ ret = bytes;
+ goto out;
+ }
+
+ if (bytes == 0)
+ break;
+ pos += bytes;
+ }
+
+ if (pos != i_size) {
+ ret = -EIO;
+ goto out;
+ }
+
+ ret = security_kernel_post_read_file(file, *buf, i_size);
+ if (!ret)
+ *size = pos;
+
+out:
+ if (ret < 0) {
+ vfree(*buf);
+ *buf = NULL;
+ }
+ return ret;
+}
+EXPORT_SYMBOL_GPL(kernel_read_file);
+
ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
{
ssize_t res = vfs_read(file, (void __user *)addr, len, &pos);