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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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