On Fri, Jul 24, 2015 at 12:04:38PM +0200, Lukasz Pawelczyk wrote:
> Add a new LSM hook called before inode's setxattr. It is required for
> LSM to be able to reliably replace the xattr's value to be set to
> filesystem in __vfs_setxattr_noperm(). Useful for mapped values, like in
> the upcoming Smack namespace patches.
>
> Signed-off-by: Lukasz Pawelczyk <l.pawelczyk@xxxxxxxxxxx>
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Could get confusing if userspace passes in 1 char and gets ENOSPC because
the unmapped label is too long :)
> ---
> fs/xattr.c | 10 ++++++++++
> include/linux/lsm_hooks.h | 9 +++++++++
> include/linux/security.h | 10 ++++++++++
> security/security.c | 12 ++++++++++++
> 4 files changed, 41 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 072fee1..cbc8d19 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -100,12 +100,22 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> if (issec)
> inode->i_flags &= ~S_NOSEC;
> if (inode->i_op->setxattr) {
> + bool alloc = false;
> +
> + error = security_inode_pre_setxattr(dentry, name, &value,
> + &size, flags, &alloc);
> + if (error)
> + return error;
> +
> error = inode->i_op->setxattr(dentry, name, value, size, flags);
> if (!error) {
> fsnotify_xattr(dentry);
> security_inode_post_setxattr(dentry, name, value,
> size, flags);
> }
> +
> + if (alloc)
> + kfree(value);
> } else if (issec) {
> const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
> error = security_inode_setsecurity(inode, suffix, value,
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 1751864..0aeed91 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -349,6 +349,11 @@
> * Check permission before setting the extended attributes
> * @value identified by @name for @dentry.
> * Return 0 if permission is granted.
> + * @inode_pre_setxattr:
> + * Be able to do some operation before setting the @value identified
> + * by @name on the filesystem. Replacing the @value and its @size is
> + * possible. Useful for mapped values. Set @alloc to true if @value
> + * needs to be kfreed afterwards.
> * @inode_post_setxattr:
> * Update inode security field after successful setxattr operation.
> * @value identified by @name for @dentry.
> @@ -1448,6 +1453,9 @@ union security_list_options {
> int (*inode_getattr)(const struct path *path);
> int (*inode_setxattr)(struct dentry *dentry, const char *name,
> const void *value, size_t size, int flags);
> + int (*inode_pre_setxattr)(struct dentry *dentry, const char *name,
> + const void **value, size_t *size,
> + int flags, bool *alloc);
> void (*inode_post_setxattr)(struct dentry *dentry, const char *name,
> const void *value, size_t size,
> int flags);
> @@ -1730,6 +1738,7 @@ struct security_hook_heads {
> struct list_head inode_setattr;
> struct list_head inode_getattr;
> struct list_head inode_setxattr;
> + struct list_head inode_pre_setxattr;
> struct list_head inode_post_setxattr;
> struct list_head inode_getxattr;
> struct list_head inode_listxattr;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index f0d2914..24f91e0 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -263,6 +263,9 @@ int security_inode_setattr(struct dentry *dentry, struct iattr *attr);
> int security_inode_getattr(const struct path *path);
> int security_inode_setxattr(struct dentry *dentry, const char *name,
> const void *value, size_t size, int flags);
> +int security_inode_pre_setxattr(struct dentry *dentry, const char *name,
> + const void **value, size_t *size, int flags,
> + bool *alloc);
> void security_inode_post_setxattr(struct dentry *dentry, const char *name,
> const void *value, size_t size, int flags);
> int security_inode_getxattr(struct dentry *dentry, const char *name);
> @@ -691,6 +694,13 @@ static inline int security_inode_setxattr(struct dentry *dentry,
> return cap_inode_setxattr(dentry, name, value, size, flags);
> }
>
> +static inline int security_inode_pre_setxattr(struct dentry *dentry,
> + const char *name, const void **value,
> + size_t *size, int flags, bool *alloc)
> +{
> + return 0;
> +}
> +
> static inline void security_inode_post_setxattr(struct dentry *dentry,
> const char *name, const void *value, size_t size, int flags)
> { }
> diff --git a/security/security.c b/security/security.c
> index 88a3b78..e1d2c6f 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -649,6 +649,16 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
> return evm_inode_setxattr(dentry, name, value, size);
> }
>
> +int security_inode_pre_setxattr(struct dentry *dentry, const char *name,
> + const void **value, size_t *size, int flags,
> + bool *alloc)
> +{
> + if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
> + return 0;
> + return call_int_hook(inode_pre_setxattr, 0, dentry, name, value, size,
> + flags, alloc);
> +}
> +
> void security_inode_post_setxattr(struct dentry *dentry, const char *name,
> const void *value, size_t size, int flags)
> {
> @@ -1666,6 +1676,8 @@ struct security_hook_heads security_hook_heads = {
> LIST_HEAD_INIT(security_hook_heads.inode_getattr),
> .inode_setxattr =
> LIST_HEAD_INIT(security_hook_heads.inode_setxattr),
> + .inode_pre_setxattr =
> + LIST_HEAD_INIT(security_hook_heads.inode_pre_setxattr),
> .inode_post_setxattr =
> LIST_HEAD_INIT(security_hook_heads.inode_post_setxattr),
> .inode_getxattr =
> --
> 2.4.3
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