linux-kernel - [PATCH v5 13/39] richacl: Check if an acl is equivalent to a file mode

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Message-Id: <1437570209-29832-14-git-send-email-andreas.gruenbacher@gmail.com>
Date:	Wed, 22 Jul 2015 15:03:03 +0200
From:	Andreas Gruenbacher <andreas.gruenbacher@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-api@...r.kernel.org, samba-technical@...ts.samba.org,
	linux-security-module@...r.kernel.org,
	Andreas Gruenbacher <agruenba@...hat.com>
Subject: [PATCH v5 13/39] richacl: Check if an acl is equivalent to a file mode

From: Andreas Gruenbacher <agruenba@...hat.com>

ACLs are considered equivalent to file modes if they only consist of owner@,
group@, and everyone@ entries, the owner@ permissions do not depend on whether
the owner is a member in the owning group, and no inheritance flags are set.
This test is used to avoid storing richacls if the acl can be computed from the
file permission bits.

Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
---
 fs/richacl_base.c       | 95 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/richacl.h |  1 +
 2 files changed, 96 insertions(+)

diff --git a/fs/richacl_base.c b/fs/richacl_base.c
index 3c13535..333faa9 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -374,3 +374,98 @@ richacl_chmod(struct richacl *acl, mode_t mode)
 	return clone;
 }
 EXPORT_SYMBOL_GPL(richacl_chmod);
+
+/**
+ * richacl_equiv_mode  -  compute the mode equivalent of @acl
+ *
+ * An acl is considered equivalent to a file mode if it only consists of
+ * owner@, group@, and everyone@ entries and the owner@ permissions do not
+ * depend on whether the owner is a member in the owning group.
+ */
+int
+richacl_equiv_mode(const struct richacl *acl, mode_t *mode_p)
+{
+	mode_t mode = *mode_p;
+
+	/*
+	 * The RICHACE_DELETE_CHILD flag is meaningless for non-directories, so
+	 * we ignore it.
+	 */
+	unsigned int x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD;
+	struct {
+		unsigned int allowed;
+		unsigned int defined;  /* allowed or denied */
+	} owner = {
+		.defined = RICHACE_POSIX_ALWAYS_ALLOWED | RICHACE_POSIX_OWNER_ALLOWED | x,
+	}, group = {
+		.defined = RICHACE_POSIX_ALWAYS_ALLOWED | x,
+	}, everyone = {
+		.defined = RICHACE_POSIX_ALWAYS_ALLOWED | x,
+	};
+	const struct richace *ace;
+
+	if (acl->a_flags & ~RICHACL_MASKED)
+		return -1;
+
+	richacl_for_each_entry(ace, acl) {
+		if (ace->e_flags & ~RICHACE_SPECIAL_WHO)
+			return -1;
+
+		if (richace_is_owner(ace) || richace_is_everyone(ace)) {
+			x = ace->e_mask & ~owner.defined;
+			if (richace_is_allow(ace)) {
+				unsigned int group_denied = group.defined & ~group.allowed;
+
+				if (x & group_denied)
+					return -1;
+				owner.allowed |= x;
+			} else /* if (richace_is_deny(ace)) */ {
+				if (x & group.allowed)
+					return -1;
+			}
+			owner.defined |= x;
+
+			if (richace_is_everyone(ace)) {
+				x = ace->e_mask;
+				if (richace_is_allow(ace)) {
+					group.allowed |= x & ~group.defined;
+					everyone.allowed |= x & ~everyone.defined;
+				}
+				group.defined |= x;
+				everyone.defined |= x;
+			}
+		} else if (richace_is_group(ace)) {
+			x = ace->e_mask & ~group.defined;
+			if (richace_is_allow(ace))
+				group.allowed |= x;
+			group.defined |= x;
+		} else
+			return -1;
+	}
+
+	if (group.allowed & ~owner.defined)
+		return -1;
+
+	if (acl->a_flags & RICHACL_MASKED) {
+		owner.allowed = acl->a_owner_mask;
+		group.allowed &= acl->a_group_mask;
+		everyone.allowed = acl->a_other_mask;
+	}
+
+	mode = (mode & ~S_IRWXUGO) |
+	       (richacl_mask_to_mode(owner.allowed) << 6) |
+	       (richacl_mask_to_mode(group.allowed) << 3) |
+		richacl_mask_to_mode(everyone.allowed);
+
+	/* Mask flags we can ignore */
+	x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD;
+
+	if (((richacl_mode_to_mask(mode >> 6) ^ owner.allowed)    & ~x) ||
+	    ((richacl_mode_to_mask(mode >> 3) ^ group.allowed)    & ~x) ||
+	    ((richacl_mode_to_mask(mode)      ^ everyone.allowed) & ~x))
+		return -1;
+
+	*mode_p = mode;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(richacl_equiv_mode);
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index f59ffa73..03876cd 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -308,6 +308,7 @@ extern unsigned int richacl_mode_to_mask(mode_t);
 extern unsigned int richacl_want_to_mask(unsigned int);
 extern void richacl_compute_max_masks(struct richacl *, kuid_t);
 extern struct richacl *richacl_chmod(struct richacl *, mode_t);
+extern int richacl_equiv_mode(const struct richacl *, mode_t *);
 
 /* richacl_inode.c */
 extern int richacl_permission(struct inode *, const struct richacl *, int);
-- 
2.4.3

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