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Date: Wed, 7 Sep 2011 17:50:22 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: agruen@...nel.org, akpm@...ux-foundation.org, dhowells@...hat.com,
linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V6 17/26] richacl: Permission check algorithm
On Mon, Sep 05, 2011 at 10:55:39PM +0530, Aneesh Kumar K.V wrote:
> From: Andreas Gruenbacher <agruen@...nel.org>
>
> As in the standard POSIX file permission model, each process is the
> owner, group, or other file class. A process is
>
> - in the owner file class if it owns the file,
> - in the group file class if it is in the file's owning group or it
> matches any of the user or group entries, and
> - in the other file class otherwise.
>
> Each file class is associated with a file mask.
>
> A richacl grants a requested access if the NFSv4 acl in the richacl
> grants the requested permissions (according to the NFSv4 permission
> check algorithm) and the file mask that applies to the process includes
> the requested permissions.
I assume that by default any ui normally recalculates an upper-bound
mask automatically when you add an ace, as the posix setfacl does, so
the user doesn't have to think about masks too much?
Patch looks right.
--b.
>
> Signed-off-by: Andreas Gruenbacher <agruen@...nel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
> fs/richacl_base.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/richacl.h | 2 +
> 2 files changed, 101 insertions(+), 0 deletions(-)
>
> diff --git a/fs/richacl_base.c b/fs/richacl_base.c
> index 60a65d7..1f885ad 100644
> --- a/fs/richacl_base.c
> +++ b/fs/richacl_base.c
> @@ -393,3 +393,102 @@ richacl_chmod(struct richacl *acl, mode_t mode)
> return clone;
> }
> EXPORT_SYMBOL_GPL(richacl_chmod);
> +
> +/**
> + * richacl_permission - richacl permission check algorithm
> + * @inode: inode to check
> + * @acl: rich acl of the inode
> + * @mask: requested access (ACE4_* bitmask)
> + *
> + * Checks if the current process is granted @mask flags in @acl.
> + */
> +int
> +richacl_permission(struct inode *inode, const struct richacl *acl,
> + unsigned int mask)
> +{
> + const struct richace *ace;
> + unsigned int requested = mask, denied = 0;
> + int in_owning_group = in_group_p(inode->i_gid);
> + int in_owner_or_group_class = in_owning_group;
> +
> + /*
> + * We don't need to know which class the process is in when the acl is
> + * not masked.
> + */
> + if (!(acl->a_flags & ACL4_MASKED))
> + in_owner_or_group_class = 1;
> +
> + /*
> + * A process is
> + * - in the owner file class if it owns the file,
> + * - in the group file class if it is in the file's owning group or
> + * it matches any of the user or group entries, and
> + * - in the other file class otherwise.
> + */
> +
> + /*
> + * Check if the acl grants the requested access and determine which
> + * file class the process is in.
> + */
> + richacl_for_each_entry(ace, acl) {
> + unsigned int ace_mask = ace->e_mask;
> +
> + if (richace_is_inherit_only(ace))
> + continue;
> + if (richace_is_owner(ace)) {
> + if (current_fsuid() != inode->i_uid)
> + continue;
> + goto is_owner;
> + } else if (richace_is_group(ace)) {
> + if (!in_owning_group)
> + continue;
> + } else if (richace_is_unix_id(ace)) {
> + if (ace->e_flags & ACE4_IDENTIFIER_GROUP) {
> + if (!in_group_p(ace->u.e_id))
> + continue;
> + } else {
> + if (current_fsuid() != ace->u.e_id)
> + continue;
> + }
> + } else
> + goto is_everyone;
> +
> +is_owner:
> + /* The process is in the owner or group file class. */
> + in_owner_or_group_class = 1;
> +
> +is_everyone:
> + /* Check which mask flags the ACE allows or denies. */
> + if (richace_is_deny(ace))
> + denied |= ace_mask & mask;
> + mask &= ~ace_mask;
> +
> + /*
> + * Keep going until we know which file class
> + * the process is in.
> + */
> + if (!mask && in_owner_or_group_class)
> + break;
> + }
> + denied |= mask;
> +
> + if (acl->a_flags & ACL4_MASKED) {
> + unsigned int file_mask;
> +
> + /*
> + * The file class a process is in determines which file mask
> + * applies. Check if that file mask also grants the requested
> + * access.
> + */
> + if (current_fsuid() == inode->i_uid)
> + file_mask = acl->a_owner_mask;
> + else if (in_owner_or_group_class)
> + file_mask = acl->a_group_mask;
> + else
> + file_mask = acl->a_other_mask;
> + denied |= requested & ~file_mask;
> + }
> +
> + return denied ? -EACCES : 0;
> +}
> +EXPORT_SYMBOL_GPL(richacl_permission);
> diff --git a/include/linux/richacl.h b/include/linux/richacl.h
> index 6dd8eb2..f46e797 100644
> --- a/include/linux/richacl.h
> +++ b/include/linux/richacl.h
> @@ -289,5 +289,7 @@ extern unsigned int richacl_mode_to_mask(mode_t);
> extern unsigned int richacl_want_to_mask(int);
> extern void richacl_compute_max_masks(struct richacl *);
> extern struct richacl *richacl_chmod(struct richacl *, mode_t);
> +extern int richacl_permission(struct inode *, const struct richacl *,
> + unsigned int);
>
> #endif /* __RICHACL_H */
> --
> 1.7.4.1
>
--
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