Re: [PATCH 1/2] ima: hooks for directory integrity protection

[Dmitry Kasatkin]

Hi,

On 12/12/13 15:39, Mimi Zohar wrote:
> On Mon, 2013-11-18 at 22:24 +0200, Dmitry Kasatkin wrote: 
>> Both IMA-appraisal and EVM protect the integrity of regular files.
>> IMA protects file data integrity, while EVM protects the file meta-data
>> integrity, such as file attributes and extended attributes. This patch
>> set adds hooks for offline directory integrity protection.
>>
>> An inode itself does not have any file name associated with it.  The
>> association of the file name to inode is done via directory entries.
>> On a running system, mandatory and/or discretionary access control prevent
>> unprivileged file deletion, file name change, or hardlink creation.
>> In an offline attack, without these protections, the association between
>> a file name and an inode is unprotected. Files can be deleted, renamed
>> or moved from one directory to another one. In all of these cases,
>> the integrity of the file data and metadata is good.
>>
>> To prevent such attacks, it is necessary to protect integrity of directory
>> content.
> Thanks Dmitry for re-posting these 'directory integrity protection'
> patches.
> The patches have evolved nicely.  Perhaps not a formal changelog, but a
> short
> summary of the major changes, would have been nice.

Will do in re-post...

>> This patch adds 2 new hooks for directory integrity protection:
>>   ima_dir_check() and ima_dir_update().
> Although these patches are probably bisect safe, as they rely on
> Kconfig, the normal ordering of patches is to define a function and use
> it in the same patch.  In the case, like here, where a new function/hook
> is defined in one subsystem, but called from another, we can split them,
> but the normal convention is to add the new function/hook first in one
> patch, and then use it in a subsequent patch.

Sorry, I did not get...

>> "normal convention is to add the new function/hook first in one
patch, and then use it in a subsequent patch. "

This is what patches do. Add hook in one patch and use in an other..

Do you mean to swap the order of these 2 patches??


>
>> ima_dir_check() is called to verify integrity of the the directory during
>> the initial path lookup.
>>
>> ima_dir_update() is called from several places in namei.c, when the directory
>> content is changing, for updating the directory hash.
>>
>> Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
>> ---
>>  fs/namei.c                        | 42 ++++++++++++++++++++++++++++++++++++---
>>  fs/open.c                         |  6 ++++++
>>  include/linux/ima.h               | 23 +++++++++++++++++++++
>>  net/unix/af_unix.c                |  2 ++
>>  security/integrity/ima/ima_main.c |  3 +++
>>  5 files changed, 73 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/namei.c b/fs/namei.c
>> index 645268f..d0e1821 100644
>> --- a/fs/namei.c
>> +++ b/fs/namei.c
>> @@ -1469,16 +1469,33 @@ static int lookup_slow(struct nameidata *nd, struct path *path)
>>  	return 0;
>>  }
>>
>> +static inline int may_lookup_ima(struct nameidata *nd, int err)
>> +{
>> +	if (err)
>> +		return err;
>> +	err = ima_dir_check(&nd->path, MAY_EXEC|MAY_NOT_BLOCK);
>> +	if (err != -ECHILD)
>> +		return err;
> A short comment here, why -ECHILD is special, would be good.

This is the same as for inode_permission().
If calling code requires locking, we have to interrupt RCU path walk and
re-start with ref path walk...

>> +	if (unlazy_walk(nd, NULL))
>> +		return -ECHILD;
>> +	return ima_dir_check(&nd->path, MAY_EXEC);
>> +}
>> +
>>  static inline int may_lookup(struct nameidata *nd)
>>  {
>> +	int err = 0;
>> +
>>  	if (nd->flags & LOOKUP_RCU) {
>> -		int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
>> +		err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
>>  		if (err != -ECHILD)
>> -			return err;
>> +			return may_lookup_ima(nd, err);
>>  		if (unlazy_walk(nd, NULL))
>>  			return -ECHILD;
>>  	}
>> -	return inode_permission(nd->inode, MAY_EXEC);
>> +	err = inode_permission(nd->inode, MAY_EXEC);
>> +	if (err)
>> +		return err;
>> +	return ima_dir_check(&nd->path, MAY_EXEC);
>>  }
>>
>>  static inline int handle_dots(struct nameidata *nd, int type)
>> @@ -2956,6 +2973,8 @@ retry_lookup:
>>  	}
>>  	mutex_lock(&dir->d_inode->i_mutex);
>>  	error = lookup_open(nd, path, file, op, got_write, opened);
>> +	if (error >= 0 && (*opened & FILE_CREATED))
>> +		ima_dir_update(&nd->path, NULL);
>>  	mutex_unlock(&dir->d_inode->i_mutex);
>>
>>  	if (error <= 0) {
>> @@ -3454,6 +3473,8 @@ retry:
>>  			error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
>>  			break;
>>  	}
>> +	if (!error)
>> +		ima_dir_update(&path, dentry);
>>  out:
>>  	done_path_create(&path, dentry);
>>  	if (retry_estale(error, lookup_flags)) {
>> @@ -3510,6 +3531,8 @@ retry:
>>  	error = security_path_mkdir(&path, dentry, mode);
>>  	if (!error)
>>  		error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
>> +	if (!error)
>> +		ima_dir_update(&path, dentry);
>>  	done_path_create(&path, dentry);
>>  	if (retry_estale(error, lookup_flags)) {
>>  		lookup_flags |= LOOKUP_REVAL;
>> @@ -3626,6 +3649,8 @@ retry:
>>  	if (error)
>>  		goto exit3;
>>  	error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
>> +	if (!error)
>> +		ima_dir_update(&nd.path, NULL);
>>  exit3:
>>  	dput(dentry);
>>  exit2:
>> @@ -3721,6 +3746,8 @@ retry:
>>  		if (error)
>>  			goto exit2;
>>  		error = vfs_unlink(nd.path.dentry->d_inode, dentry);
>> +		if (!error)
>> +			ima_dir_update(&nd.path, NULL);
>>  exit2:
>>  		dput(dentry);
>>  	}
>> @@ -3801,6 +3828,8 @@ retry:
>>  	error = security_path_symlink(&path, dentry, from->name);
>>  	if (!error)
>>  		error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
>> +	if (!error)
>> +		ima_dir_update(&path, dentry);
>>  	done_path_create(&path, dentry);
>>  	if (retry_estale(error, lookup_flags)) {
>>  		lookup_flags |= LOOKUP_REVAL;
>> @@ -3919,6 +3948,8 @@ retry:
>>  	if (error)
>>  		goto out_dput;
>>  	error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
>> +	if (!error)
>> +		ima_dir_update(&new_path, NULL);
>>  out_dput:
>>  	done_path_create(&new_path, new_dentry);
>>  	if (retry_estale(error, how)) {
>> @@ -4171,6 +4202,11 @@ retry:
>>  		goto exit5;
>>  	error = vfs_rename(old_dir->d_inode, old_dentry,
>>  				   new_dir->d_inode, new_dentry);
>> +	if (!error) {
>> +		ima_dir_update(&oldnd.path, NULL);
>> +		if (!path_equal(&oldnd.path, &newnd.path))
>> +			ima_dir_update(&newnd.path, NULL);
>> +	}
>>  exit5:
>>  	dput(new_dentry);
>>  exit4:
>> diff --git a/fs/open.c b/fs/open.c
>> index d420331..021e2c5 100644
>> --- a/fs/open.c
>> +++ b/fs/open.c
>> @@ -390,6 +390,9 @@ retry:
>>  	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
>>  	if (error)
>>  		goto dput_and_out;
>> +	error = ima_dir_check(&path, MAY_EXEC);
>> +	if (error)
>> +		goto dput_and_out;
>>
>>  	set_fs_pwd(current->fs, &path);
>>
>> @@ -420,6 +423,9 @@ SYSCALL_DEFINE1(fchdir, unsigned int, fd)
>>  		goto out_putf;
>>
>>  	error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
>> +	if (error)
>> +		goto out_putf;
>> +	error = ima_dir_check(&f.file->f_path, MAY_EXEC);
>>  	if (!error)
>>  		set_fs_pwd(current->fs, &f.file->f_path);
>>  out_putf:
>> diff --git a/include/linux/ima.h b/include/linux/ima.h
>> index 1b7f268..e33035e 100644
>> --- a/include/linux/ima.h
>> +++ b/include/linux/ima.h
>> @@ -73,4 +73,27 @@ static inline int ima_inode_removexattr(struct dentry *dentry,
>>  	return 0;
>>  }
>>  #endif /* CONFIG_IMA_APPRAISE */
>> +
>> +#ifdef CONFIG_IMA_APPRAISE_DIRECTORIES
>> +extern int ima_dir_check(struct path *dir, int mask);
>> +extern int ima_special_check(struct file *file, int mask);
> No mention was made of this new hook.  This should be a separate patch,
> with its own patch description.

Yes. This is a patch split mistake.. Thanks.

>
> thanks,
>
> Mimi
>
>> +extern void ima_dir_update(struct path *dir, struct dentry *dentry);
>> +#else
>> +static inline int ima_dir_check(struct path *dir, int mask)
>> +{
>> +	return 0;
>> +}
>> +
>> +static inline int ima_special_check(struct file *file, int mask)
>> +{
>> +	return 0;
>> +}
>> +
>> +static inline void ima_dir_update(struct path *dir, struct dentry *dentry)
>> +{
>> +	return;
>> +}
>> +
>> +#endif /* CONFIG_IMA_APPRAISE_DIRECTORIES */
>> +
>>  #endif /* _LINUX_IMA_H */
>> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
>> index 86de99a..6230a50 100644
>> --- a/net/unix/af_unix.c
>> +++ b/net/unix/af_unix.c
>> @@ -115,6 +115,7 @@
>>  #include <net/checksum.h>
>>  #include <linux/security.h>
>>  #include <linux/freezer.h>
>> +#include <linux/ima.h>
>>
>>  struct hlist_head unix_socket_table[2 * UNIX_HASH_SIZE];
>>  EXPORT_SYMBOL_GPL(unix_socket_table);
>> @@ -841,6 +842,7 @@ static int unix_mknod(const char *sun_path, umode_t mode, struct path *res)
>>  		if (!err) {
>>  			res->mnt = mntget(path.mnt);
>>  			res->dentry = dget(dentry);
>> +			ima_dir_update(&path, dentry);
>>  		}
>>  	}
>>  	done_path_create(&path, dentry);
>> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
>> index 6c12811..18d76d8 100644
>> --- a/security/integrity/ima/ima_main.c
>> +++ b/security/integrity/ima/ima_main.c
>> @@ -300,6 +300,9 @@ int ima_bprm_check(struct linux_binprm *bprm)
>>   */
>>  int ima_file_check(struct file *file, int mask)
>>  {
>> +	if (!S_ISREG(file->f_dentry->d_inode->i_mode))
>> +		return ima_special_check(file, mask);
>> +
>>  	ima_rdwr_violation_check(file);
>>  	return process_measurement(file, NULL,
>>  				   mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
>
>

Thanks

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