Re: [RFC PATCH v2 06/11] kexec: replace call to copy_file_from_fd() with kernel version

[Dave Young <dyoung@redhat.com>]

Hi, Mimi

Besides of code issues, I have several thing to be understand:

What is the effect to kexec behavior with this patchset?
  - without IMA enabled (kconfig or kernel cmdline) it will be same as before?
  - with IMA enabled for kernel bzImage, kexec_file_load will check both ima
    signature and original pe file signature, those two mechanisms are
    somehow duplicated. I'm not sure if we need both for bzImage.

Do you have a simple usage documentation about how to test it?

On 01/18/16 at 10:11am, Mimi Zohar wrote:
> This patch defines kernel_read_file_from_fd(), a wrapper for the VFS
> common kernel_read_file(), and replaces the kexec copy_file_from_fd()
> calls with the kernel_read_file_from_fd() wrapper.
> 
> Two new IMA policy identifiers named KEXEC_CHECK and INITRAMFS_CHECK
> are defined for measuring, appraising or auditing the kexec image
> and initramfs.
> 
> Changelog v1:
> - re-order and squash the kexec patches
> 
> v3: ima: measure and appraise kexec image and initramfs (squashed)
> - rename ima_read_hooks enumeration to ima_policy_id
> - use kstat file size type loff_t, not size_t
> - add union name "hooks" to fix sparse warning
> 
> v2:
> - Calculate the file hash from the in memory buffer
> (suggested by Dave Young)
> - Rename ima_read_and_process_file() to ima_hash_and_process_file()
> - replace individual case statements with range:
>         KEXEC_CHECK ... IMA_MAX_READ_CHECK - 1
> v1:
> - Instead of ima_read_and_process_file() allocating memory, the caller
> allocates and frees the memory.
> - Moved the kexec measurement/appraisal call to copy_file_from_fd(). The
> same call now measures and appraises both the kexec image and initramfs.
> 
> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> ---
>  Documentation/ABI/testing/ima_policy  |  2 +-
>  fs/exec.c                             | 15 ++++++++
>  include/linux/fs.h                    |  1 +
>  include/linux/ima.h                   |  2 +
>  kernel/kexec_file.c                   | 72 ++++-------------------------------
>  security/integrity/ima/ima.h          |  9 ++++-
>  security/integrity/ima/ima_appraise.c |  7 ++++
>  security/integrity/ima/ima_policy.c   | 27 ++++++++++---
>  8 files changed, 64 insertions(+), 71 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index 0a378a8..e80f767 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -26,7 +26,7 @@ Description:
>  			option:	[[appraise_type=]] [permit_directio]
>  
>  		base: 	func:= [BPRM_CHECK][MMAP_CHECK][FILE_CHECK][MODULE_CHECK]
> -				[FIRMWARE_CHECK]
> +				[FIRMWARE_CHECK] [KEXEC_CHECK] [INITRAMFS_CHECK]
>  			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
>  			       [[^]MAY_EXEC]
>  			fsmagic:= hex value
> diff --git a/fs/exec.c b/fs/exec.c
> index 211b81c..a5ae51e 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -884,6 +884,21 @@ out:
>  }
>  EXPORT_SYMBOL_GPL(kernel_read_file);
>  
> +int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
> +			     int policy_id)

Though this is only used in kexec now, it looks more a general function, move it
to general code should be fine along with kernel_read_file 

> +{
> +	struct fd f = fdget(fd);
> +	int ret = -ENOEXEC;

-EBADF looks better?

> +
> +	if (!f.file)
> +		goto out;
> +
> +	ret = kernel_read_file(f.file, buf, size, max_size, policy_id);
> +out:
> +	fdput(f);
> +	return ret;
> +}
> +
>  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);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 9b1468c..9642623 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2528,6 +2528,7 @@ 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, int);
> +extern int kernel_read_file_from_fd(int, void **, loff_t *, loff_t, int);
>  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 *);
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index ca76f60..ae91938 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -14,6 +14,8 @@
>  struct linux_binprm;
>  
>  enum ima_policy_id {
> +	KEXEC_CHECK = 1,
> +	INITRAMFS_CHECK,

Change to below should be better:
KEXEC_KERNEL_CHECK
KEXEC_INITRAMFS_CHECK

>  	IMA_MAX_READ_CHECK
>  };
>  
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index b70ada0..f7c3ce4 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -18,6 +18,7 @@
>  #include <linux/kexec.h>
>  #include <linux/mutex.h>
>  #include <linux/list.h>
> +#include <linux/ima.h>
>  #include <crypto/hash.h>
>  #include <crypto/sha.h>
>  #include <linux/syscalls.h>
> @@ -33,65 +34,6 @@ size_t __weak kexec_purgatory_size = 0;
>  
>  static int kexec_calculate_store_digests(struct kimage *image);
>  
> -static int copy_file_from_fd(int fd, void **buf, unsigned long *buf_len)
> -{
> -	struct fd f = fdget(fd);
> -	int ret;
> -	struct kstat stat;
> -	loff_t pos;
> -	ssize_t bytes = 0;
> -
> -	if (!f.file)
> -		return -EBADF;
> -
> -	ret = vfs_getattr(&f.file->f_path, &stat);
> -	if (ret)
> -		goto out;
> -
> -	if (stat.size > INT_MAX) {
> -		ret = -EFBIG;
> -		goto out;
> -	}
> -
> -	/* Don't hand 0 to vmalloc, it whines. */
> -	if (stat.size == 0) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> -
> -	*buf = vmalloc(stat.size);
> -	if (!*buf) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> -
> -	pos = 0;
> -	while (pos < stat.size) {
> -		bytes = kernel_read(f.file, pos, (char *)(*buf) + pos,
> -				    stat.size - pos);
> -		if (bytes < 0) {
> -			vfree(*buf);
> -			ret = bytes;
> -			goto out;
> -		}
> -
> -		if (bytes == 0)
> -			break;
> -		pos += bytes;
> -	}
> -
> -	if (pos != stat.size) {
> -		ret = -EBADF;
> -		vfree(*buf);
> -		goto out;
> -	}
> -
> -	*buf_len = pos;
> -out:
> -	fdput(f);
> -	return ret;
> -}
> -
>  /* Architectures can provide this probe function */
>  int __weak arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
>  					 unsigned long buf_len)
> @@ -180,16 +122,17 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  {
>  	int ret = 0;
>  	void *ldata;
> +	loff_t size;
>  
> -	ret = copy_file_from_fd(kernel_fd, &image->kernel_buf,
> -				&image->kernel_buf_len);
> +	ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
> +				       &size, INT_MAX, KEXEC_CHECK);
>  	if (ret)
>  		return ret;
> +	image->kernel_buf_len = size;
>  
>  	/* Call arch image probe handlers */
>  	ret = arch_kexec_kernel_image_probe(image, image->kernel_buf,
>  					    image->kernel_buf_len);
> -
>  	if (ret)
>  		goto out;
>  
> @@ -204,10 +147,11 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  #endif
>  	/* It is possible that there no initramfs is being loaded */
>  	if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
> -		ret = copy_file_from_fd(initrd_fd, &image->initrd_buf,
> -					&image->initrd_buf_len);
> +		ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,
> +					       &size, INT_MAX, INITRAMFS_CHECK);
>  		if (ret)
>  			goto out;
> +		image->initrd_buf_len = size;
>  	}
>  
>  	if (cmdline_len) {
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 06bcc24..b98dbd5 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -160,7 +160,14 @@ void ima_free_template_entry(struct ima_template_entry *entry);
>  const char *ima_d_path(struct path *path, char **pathbuf);
>  
>  /* IMA policy related functions */
> -enum ima_hooks { FILE_CHECK = 1, MMAP_CHECK, BPRM_CHECK, MODULE_CHECK, FIRMWARE_CHECK, POST_SETATTR };
> +enum ima_hooks {
> +	FILE_CHECK = IMA_MAX_READ_CHECK,
> +	MMAP_CHECK,
> +	BPRM_CHECK,
> +	MODULE_CHECK,
> +	FIRMWARE_CHECK,
> +	POST_SETATTR
> +};
>  
>  int ima_match_policy(struct inode *inode, int func, int mask, int flags);
>  void ima_init_policy(void);
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 4edf47f..3adf937 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -78,6 +78,8 @@ enum integrity_status ima_get_cache_status(struct integrity_iint_cache *iint,
>  		return iint->ima_module_status;
>  	case FIRMWARE_CHECK:
>  		return iint->ima_firmware_status;
> +	case KEXEC_CHECK ... IMA_MAX_READ_CHECK - 1:
> +		return iint->ima_read_status;
>  	case FILE_CHECK:
>  	default:
>  		return iint->ima_file_status;
> @@ -100,6 +102,9 @@ static void ima_set_cache_status(struct integrity_iint_cache *iint,
>  	case FIRMWARE_CHECK:
>  		iint->ima_firmware_status = status;
>  		break;
> +	case KEXEC_CHECK ... IMA_MAX_READ_CHECK - 1:
> +		iint->ima_read_status = status;
> +		break;
>  	case FILE_CHECK:
>  	default:
>  		iint->ima_file_status = status;
> @@ -122,6 +127,8 @@ static void ima_cache_flags(struct integrity_iint_cache *iint, int func)
>  	case FIRMWARE_CHECK:
>  		iint->flags |= (IMA_FIRMWARE_APPRAISED | IMA_APPRAISED);
>  		break;
> +	case KEXEC_CHECK ... IMA_MAX_READ_CHECK - 1:
> +		break;
>  	case FILE_CHECK:
>  	default:
>  		iint->flags |= (IMA_FILE_APPRAISED | IMA_APPRAISED);
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 595e038..4711083 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -306,6 +306,8 @@ static int get_subaction(struct ima_rule_entry *rule, int func)
>  		return IMA_MODULE_APPRAISE;
>  	case FIRMWARE_CHECK:
>  		return IMA_FIRMWARE_APPRAISE;
> +	case KEXEC_CHECK ... IMA_MAX_READ_CHECK - 1:
> +		return IMA_READ_APPRAISE;
>  	case FILE_CHECK:
>  	default:
>  		return IMA_FILE_APPRAISE;
> @@ -614,6 +616,10 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
>  				entry->hooks.func = MMAP_CHECK;
>  			else if (strcmp(args[0].from, "BPRM_CHECK") == 0)
>  				entry->hooks.func = BPRM_CHECK;
> +			else if (strcmp(args[0].from, "KEXEC_CHECK") == 0)
> +				entry->hooks.policy_id = KEXEC_CHECK;
> +			else if (strcmp(args[0].from, "INITRAMFS_CHECK") == 0)
> +				entry->hooks.policy_id = INITRAMFS_CHECK;
>  			else
>  				result = -EINVAL;
>  			if (!result)
> @@ -867,7 +873,9 @@ static char *func_tokens[] = {
>  	"BPRM_CHECK",
>  	"MODULE_CHECK",
>  	"FIRMWARE_CHECK",
> -	"POST_SETATTR"
> +	"POST_SETATTR",
> +	"KEXEC_CHECK",
> +	"INITRAMFS_CHECK",
>  };
>  
>  void *ima_policy_start(struct seq_file *m, loff_t *pos)
> @@ -948,10 +956,19 @@ int ima_policy_show(struct seq_file *m, void *v)
>  			seq_printf(m, pt(Opt_func), ft(func_post));
>  			break;
>  		default:
> -			snprintf(tbuf, sizeof(tbuf), "%d",
> -				 entry->hooks.func);
> -			seq_printf(m, pt(Opt_func), tbuf);
> -			break;
> +			switch (entry->hooks.policy_id) {
> +			case KEXEC_CHECK:
> +				seq_printf(m, pt(Opt_func), ft(func_kexec));
> +				break;
> +			case INITRAMFS_CHECK:
> +				seq_printf(m, pt(Opt_func), ft(func_initramfs));
> +				break;
> +			default:
> +				snprintf(tbuf, sizeof(tbuf), "%d",
> +					 entry->hooks.func);
> +				seq_printf(m, pt(Opt_func), tbuf);
> +				break;
> +			}
>  		}
>  		seq_puts(m, " ");
>  	}
> -- 
> 2.1.0
> 
> 
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