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Date: Wed, 13 Jul 2016 10:59:35 -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 6/9] security, overlayfs: Provide hook to correctly label
newly created files
On 07/13/2016 10:57 AM, Stephen Smalley wrote:
> On 07/13/2016 10:44 AM, Vivek Goyal wrote:
>> During a new file creation we need to make sure new file is created with the
>> right label. New file is created in upper/ so effectively file should get
>> label as if task had created file in upper/.
>>
>> We switched to mounter's creds for actual file creation. Also if there is a
>> whiteout present, then file will be created in work/ dir first and then
>> renamed in upper. In none of the cases file will be labeled as we want it to
>> be.
>>
>> This patch introduces a new hook dentry_create_files_as(), which determines
>> the label/context dentry will get if it had been created by task in upper
>> and modify passed set of creds appropriately. Caller makes use of these new
>> creds for file creation.
>>
>> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
>> ---
>> fs/overlayfs/dir.c | 10 ++++++++++
>> include/linux/lsm_hooks.h | 15 +++++++++++++++
>> include/linux/security.h | 12 ++++++++++++
>> security/security.c | 11 +++++++++++
>> 4 files changed, 48 insertions(+)
>>
>> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
>> index 4cdeb74..f94872f 100644
>> --- a/fs/overlayfs/dir.c
>> +++ b/fs/overlayfs/dir.c
>> @@ -433,6 +433,15 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
>> if (override_cred) {
>> override_cred->fsuid = inode->i_uid;
>> override_cred->fsgid = inode->i_gid;
>> + if (!hardlink) {
>> + err = security_dentry_create_files_as(dentry,
>> + mode, &dentry->d_name, old_cred,
>> + override_cred);
>> + if (err) {
>> + put_cred(override_cred);
>
> Same principle here; on error the caller should do nothing with
> override_cred.
Sorry, never mind - not allocated by the hook so properly handled by the
caller.
>
>> + goto out_revert_creds;
>> + }
>> + }
>> put_cred(override_creds(override_cred));
>> put_cred(override_cred);
>>
>> @@ -443,6 +452,7 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
>> err = ovl_create_over_whiteout(dentry, inode, &stat,
>> link, hardlink);
>> }
>> +out_revert_creds:
>> revert_creds(old_cred);
>> if (!err) {
>> struct inode *realinode = d_inode(ovl_dentry_upper(dentry));
>> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
>> index 84caead..95745fe 100644
>> --- a/include/linux/lsm_hooks.h
>> +++ b/include/linux/lsm_hooks.h
>> @@ -151,6 +151,16 @@
>> * @name name of the last path component used to create file
>> * @ctx pointer to place the pointer to the resulting context in.
>> * @ctxlen point to place the length of the resulting context.
>> + * @dentry_create_files_as:
>> + * Compute a context for a dentry as the inode is not yet available
>> + * and set that context in passed in creds so that new files are
>> + * created using that context. Context is calculated using the
>> + * passed in creds and not the creds of the caller.
>> + * @dentry dentry to use in calculating the context.
>> + * @mode mode used to determine resource type.
>> + * @name name of the last path component used to create file
>> + * @old creds which should be used for context calculation
>> + * @new creds to modify
>> *
>> *
>> * Security hooks for inode operations.
>> @@ -1375,6 +1385,10 @@ union security_list_options {
>> int (*dentry_init_security)(struct dentry *dentry, int mode,
>> struct qstr *name, void **ctx,
>> u32 *ctxlen);
>> + int (*dentry_create_files_as)(struct dentry *dentry, int mode,
>> + struct qstr *name,
>> + const struct cred *old,
>> + struct cred *new);
>>
>>
>> #ifdef CONFIG_SECURITY_PATH
>> @@ -1675,6 +1689,7 @@ struct security_hook_heads {
>> struct list_head sb_clone_mnt_opts;
>> struct list_head sb_parse_opts_str;
>> struct list_head dentry_init_security;
>> + struct list_head dentry_create_files_as;
>> #ifdef CONFIG_SECURITY_PATH
>> struct list_head path_unlink;
>> struct list_head path_mkdir;
>> diff --git a/include/linux/security.h b/include/linux/security.h
>> index 4a3b8bc..1eb03dc 100644
>> --- a/include/linux/security.h
>> +++ b/include/linux/security.h
>> @@ -242,6 +242,10 @@ int security_sb_parse_opts_str(char *options, struct security_mnt_opts *opts);
>> int security_dentry_init_security(struct dentry *dentry, int mode,
>> struct qstr *name, void **ctx,
>> u32 *ctxlen);
>> +int security_dentry_create_files_as(struct dentry *dentry, int mode,
>> + struct qstr *name,
>> + const struct cred *old,
>> + struct cred *new);
>>
>> int security_inode_alloc(struct inode *inode);
>> void security_inode_free(struct inode *inode);
>> @@ -600,6 +604,14 @@ static inline int security_dentry_init_security(struct dentry *dentry,
>> return -EOPNOTSUPP;
>> }
>>
>> +static inline int security_dentry_create_files_as(struct dentry *dentry,
>> + int mode, struct qstr *name,
>> + const struct cred *old,
>> + struct cred *new)
>> +{
>> + return 0;
>> +}
>> +
>>
>> static inline int security_inode_init_security(struct inode *inode,
>> struct inode *dir,
>> diff --git a/security/security.c b/security/security.c
>> index 3321e31..38747d1 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -364,6 +364,15 @@ int security_dentry_init_security(struct dentry *dentry, int mode,
>> }
>> EXPORT_SYMBOL(security_dentry_init_security);
>>
>> +int security_dentry_create_files_as(struct dentry *dentry, int mode,
>> + struct qstr *name,
>> + const struct cred *old, struct cred *new)
>> +{
>> + return call_int_hook(dentry_create_files_as, 0, dentry, mode,
>> + name, old, new);
>> +}
>> +EXPORT_SYMBOL(security_dentry_create_files_as);
>> +
>> int security_inode_init_security(struct inode *inode, struct inode *dir,
>> const struct qstr *qstr,
>> const initxattrs initxattrs, void *fs_data)
>> @@ -1614,6 +1623,8 @@ struct security_hook_heads security_hook_heads = {
>> LIST_HEAD_INIT(security_hook_heads.sb_parse_opts_str),
>> .dentry_init_security =
>> LIST_HEAD_INIT(security_hook_heads.dentry_init_security),
>> + .dentry_create_files_as =
>> + LIST_HEAD_INIT(security_hook_heads.dentry_create_files_as),
>> #ifdef CONFIG_SECURITY_PATH
>> .path_unlink = LIST_HEAD_INIT(security_hook_heads.path_unlink),
>> .path_mkdir = LIST_HEAD_INIT(security_hook_heads.path_mkdir),
>>
>
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