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Commit b44a7dfc authored by Mimi Zohar's avatar Mimi Zohar
Browse files

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: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: default avatarLuis R. Rodriguez <mcgrof@suse.com>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
parent 4b2530d8

fs/exec.c

+53 −0
Original line number Diff line number Diff line
@@ -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 @@ int kernel_read(struct file *file, loff_t offset, 


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);

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -2577,6 +2577,7 @@ static inline void i_readcount_inc(struct inode *inode) 
extern int do_pipe_flags(int *, int);



extern int kernel_read(struct file *, loff_t, char *, unsigned long);

extern int kernel_read_file(struct file *, void **, loff_t *, loff_t);

extern ssize_t kernel_write(struct file *, const char *, size_t, loff_t);

extern ssize_t __kernel_write(struct file *, const char *, size_t, loff_t *);

extern struct file * open_exec(const char *);

include/linux/lsm_hooks.h

+9 −0
Original line number Diff line number Diff line
@@ -561,6 +561,13 @@ 
 *	the kernel module to load. If the module is being loaded from a blob,

 *	this argument will be NULL.

 *	Return 0 if permission is granted.

 * @kernel_post_read_file:

 *	Read a file specified by userspace.

 *	@file contains the file structure pointing to the file being read

 *	by the kernel.

 *	@buf pointer to buffer containing the file contents.

 *	@size length of the file contents.

 *	Return 0 if permission is granted.

 * @task_fix_setuid:

 *	Update the module's state after setting one or more of the user

 *	identity attributes of the current process.  The @flags parameter
@@ -1457,6 +1464,7 @@ union security_list_options { 
	int (*kernel_fw_from_file)(struct file *file, char *buf, size_t size);

	int (*kernel_module_request)(char *kmod_name);

	int (*kernel_module_from_file)(struct file *file);

	int (*kernel_post_read_file)(struct file *file, char *buf, loff_t size);

	int (*task_fix_setuid)(struct cred *new, const struct cred *old,

				int flags);

	int (*task_setpgid)(struct task_struct *p, pid_t pgid);
@@ -1716,6 +1724,7 @@ struct security_hook_heads { 
	struct list_head kernel_act_as;

	struct list_head kernel_create_files_as;

	struct list_head kernel_fw_from_file;

	struct list_head kernel_post_read_file;

	struct list_head kernel_module_request;

	struct list_head kernel_module_from_file;

	struct list_head task_fix_setuid;

include/linux/security.h

+7 −0
Original line number Diff line number Diff line
@@ -301,6 +301,7 @@ int security_kernel_create_files_as(struct cred *new, struct inode *inode); 
int security_kernel_fw_from_file(struct file *file, char *buf, size_t size);

int security_kernel_module_request(char *kmod_name);

int security_kernel_module_from_file(struct file *file);

int security_kernel_post_read_file(struct file *file, char *buf, loff_t size);

int security_task_fix_setuid(struct cred *new, const struct cred *old,

			     int flags);

int security_task_setpgid(struct task_struct *p, pid_t pgid);
@@ -866,6 +867,12 @@ static inline int security_kernel_module_from_file(struct file *file) 
	return 0;

}



static inline int security_kernel_post_read_file(struct file *file,

						 char *buf, loff_t size)

{

	return 0;

}



static inline int security_task_fix_setuid(struct cred *new,

					   const struct cred *old,

					   int flags)

security/security.c

+8 −0
Original line number Diff line number Diff line
@@ -910,6 +910,12 @@ int security_kernel_module_from_file(struct file *file) 
	return ima_module_check(file);

}



int security_kernel_post_read_file(struct file *file, char *buf, loff_t size)

{

	return call_int_hook(kernel_post_read_file, 0, file, buf, size);

}

EXPORT_SYMBOL_GPL(security_kernel_post_read_file);



int security_task_fix_setuid(struct cred *new, const struct cred *old,

			     int flags)

{
@@ -1697,6 +1703,8 @@ struct security_hook_heads security_hook_heads = { 
		LIST_HEAD_INIT(security_hook_heads.kernel_module_request),

	.kernel_module_from_file =

		LIST_HEAD_INIT(security_hook_heads.kernel_module_from_file),

	.kernel_post_read_file =

		LIST_HEAD_INIT(security_hook_heads.kernel_post_read_file),

	.task_fix_setuid =

		LIST_HEAD_INIT(security_hook_heads.task_fix_setuid),

	.task_setpgid =	LIST_HEAD_INIT(security_hook_heads.task_setpgid),