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Subject[PATCH -V3 11/17] richacl: Check if an acl is equivalent to a file mode
Date
From: Andreas Gruenbacher <agruen@suse.de>

This function is used to avoid storing richacls on disk if the acl can
be computed from the file permission bits.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/richacl_base.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++
include/linux/richacl.h | 1 +
2 files changed, 55 insertions(+), 0 deletions(-)
diff --git a/fs/richacl_base.c b/fs/richacl_base.c
index 6074116..5afdc5a 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -541,3 +541,57 @@ richacl_inherit(const struct richacl *dir_acl, int isdir)

return acl;
}
+
+/**
+ * richacl_equiv_mode - check if @acl is equivalent to file permission bits
+ * @mode_p: the file mode (including the file type)
+ *
+ * If @acl can be fully represented by file permission bits, this function
+ * returns 0, and the file permission bits in @mode_p are set to the equivalent
+ * of @acl.
+ *
+ * This function is used to avoid storing richacls on disk if the acl can be
+ * computed from the file permission bits. It allows user-space to make sure
+ * that a file has no explicit richacl set.
+ */
+int
+richacl_equiv_mode(const struct richacl *acl, mode_t *mode_p)
+{
+ const struct richace *ace = acl->a_entries;
+ unsigned int x;
+ mode_t mode;
+
+ if (acl->a_count != 1 ||
+ acl->a_flags != ACL4_MASKED ||
+ !richace_is_everyone(ace) ||
+ !richace_is_allow(ace) ||
+ ace->e_flags & ~ACE4_SPECIAL_WHO)
+ return -1;
+
+ /*
+ * Figure out the permissions we care about: ACE4_DELETE_CHILD is
+ * meaningless for non-directories, so we ignore it.
+ */
+ x = ~ACE4_POSIX_ALWAYS_ALLOWED;
+ if (!S_ISDIR(*mode_p))
+ x &= ~ACE4_DELETE_CHILD;
+
+ mode = richacl_masks_to_mode(acl);
+ if ((acl->a_group_mask & x) != (richacl_mode_to_mask(mode >> 3) & x) ||
+ (acl->a_other_mask & x) != (richacl_mode_to_mask(mode) & x))
+ return -1;
+
+ /*
+ * Ignore permissions which the owner is always allowed.
+ */
+ x &= ~ACE4_POSIX_OWNER_ALLOWED;
+ if ((acl->a_owner_mask & x) != (richacl_mode_to_mask(mode >> 6) & x))
+ return -1;
+
+ if ((ace->e_mask & x) != (ACE4_POSIX_MODE_ALL & x))
+ return -1;
+
+ *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(richacl_equiv_mode);
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index 05d2319..6151770 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -292,6 +292,7 @@ extern struct richacl *richacl_chmod(struct richacl *, mode_t);
extern int richacl_permission(struct inode *, const struct richacl *,
unsigned int);
extern struct richacl *richacl_inherit(const struct richacl *, int);
+extern int richacl_equiv_mode(const struct richacl *, mode_t *);

/* richacl_inode.c */

--
1.7.0.4


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