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Message-ID: <26a1232e-09b2-e89b-22c3-7414dd11e79c@tycho.nsa.gov>
Date: Mon, 11 Jul 2016 11:24:26 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Vivek Goyal <vgoyal@...hat.com>, miklos@...redi.hu,
pmoore@...hat.com, casey@...aufler-ca.com,
linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org,
linux-security-module@...r.kernel.org
Cc: dwalsh@...hat.com, dhowells@...hat.com, viro@...IV.linux.org.uk,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/7] security, overlayfs: provide copy up security hook
for unioned files
On 07/08/2016 12:19 PM, Vivek Goyal wrote:
> Provide a security hook to label new file correctly when a file is copied
> up from lower layer to upper layer of a overlay/union mount.
>
> This hook can prepare a new set of creds which are suitable for new file
> creation during copy up. Caller will use new creds to create file and then
> revert back to old creds and release new creds.
>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
> fs/overlayfs/copy_up.c | 18 ++++++++++++++++++
> include/linux/lsm_hooks.h | 11 +++++++++++
> include/linux/security.h | 6 ++++++
> security/security.c | 8 ++++++++
> 4 files changed, 43 insertions(+)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 80aa6f1..8ebea18 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -246,6 +246,8 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
> struct dentry *upper = NULL;
> umode_t mode = stat->mode;
> int err;
> + const struct cred *old_creds = NULL;
> + struct cred *new_creds = NULL;
>
> newdentry = ovl_lookup_temp(workdir, dentry);
> err = PTR_ERR(newdentry);
> @@ -258,10 +260,26 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
> if (IS_ERR(upper))
> goto out1;
>
> + err = security_inode_copy_up(dentry, &new_creds);
> + if (err < 0) {
> + if (new_creds)
> + put_cred(new_creds);
Why do we need a put_cred() here?
> + goto out2;
> + }
> +
> + if (new_creds)
> + old_creds = override_creds(new_creds);
> +
> /* Can't properly set mode on creation because of the umask */
> stat->mode &= S_IFMT;
> err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
> stat->mode = mode;
> +
> + if (new_creds) {
> + revert_creds(old_creds);
> + put_cred(new_creds);
> + }
> +
> if (err)
> goto out2;
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 7ae3976..c1f95be 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -401,6 +401,15 @@
> * @inode contains a pointer to the inode.
> * @secid contains a pointer to the location where result will be saved.
> * In case of failure, @secid will be set to zero.
> + * @inode_copy_up:
> + * A file is about to be copied up from lower layer to upper layer of
> + * overlay filesystem. Security module can prepare a set of new creds
> + * and modify as need be and return new creds. Caller will switch to
> + * new creds temporarily to create new file and release newly allocated
> + * creds.
> + * @src indicates the union dentry of file that is being copied up.
> + * @new pointer to pointer to return newly allocated creds.
> + * Returns 0 on success or a negative error code on error.
> *
> * Security hooks for file operations
> *
> @@ -1425,6 +1434,7 @@ union security_list_options {
> int (*inode_listsecurity)(struct inode *inode, char *buffer,
> size_t buffer_size);
> void (*inode_getsecid)(struct inode *inode, u32 *secid);
> + int (*inode_copy_up) (struct dentry *src, struct cred **new);
>
> int (*file_permission)(struct file *file, int mask);
> int (*file_alloc_security)(struct file *file);
> @@ -1696,6 +1706,7 @@ struct security_hook_heads {
> struct list_head inode_setsecurity;
> struct list_head inode_listsecurity;
> struct list_head inode_getsecid;
> + struct list_head inode_copy_up;
> struct list_head file_permission;
> struct list_head file_alloc_security;
> struct list_head file_free_security;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 14df373..c976d79 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -282,6 +282,7 @@ int security_inode_getsecurity(struct inode *inode, const char *name, void **buf
> int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags);
> int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size);
> void security_inode_getsecid(struct inode *inode, u32 *secid);
> +int security_inode_copy_up(struct dentry *src, struct cred **new);
> int security_file_permission(struct file *file, int mask);
> int security_file_alloc(struct file *file);
> void security_file_free(struct file *file);
> @@ -758,6 +759,11 @@ static inline void security_inode_getsecid(struct inode *inode, u32 *secid)
> *secid = 0;
> }
>
> +static inline int security_inode_copy_up(struct dentry *src, struct cred **new)
> +{
> + return 0;
> +}
> +
> static inline int security_file_permission(struct file *file, int mask)
> {
> return 0;
> diff --git a/security/security.c b/security/security.c
> index 7095693..3d142aa 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -727,6 +727,12 @@ void security_inode_getsecid(struct inode *inode, u32 *secid)
> call_void_hook(inode_getsecid, inode, secid);
> }
>
> +int security_inode_copy_up(struct dentry *src, struct cred **new)
> +{
> + return call_int_hook(inode_copy_up, 0, src, new);
> +}
> +EXPORT_SYMBOL(security_inode_copy_up);
> +
> int security_file_permission(struct file *file, int mask)
> {
> int ret;
> @@ -1663,6 +1669,8 @@ struct security_hook_heads security_hook_heads = {
> LIST_HEAD_INIT(security_hook_heads.inode_listsecurity),
> .inode_getsecid =
> LIST_HEAD_INIT(security_hook_heads.inode_getsecid),
> + .inode_copy_up =
> + LIST_HEAD_INIT(security_hook_heads.inode_copy_up),
> .file_permission =
> LIST_HEAD_INIT(security_hook_heads.file_permission),
> .file_alloc_security =
>
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