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Date: Thu, 12 Dec 2013 08:39:37 -0500
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Dmitry Kasatkin <d.kasatkin@...sung.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
viro@...iv.linux.org.uk, linux-security-module@...r.kernel.org,
jmorris@...ei.org, dmitry.kasatkin@...il.com
Subject: Re: [PATCH 1/2] ima: hooks for directory integrity protection
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.
>
> 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.
>
> 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@...sung.com>
> ---
> 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.
> + 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.
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),
--
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