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    Subject[PATCH -V7 16/26] richacl: Update the file masks in chmod()
    Date
    From: Andreas Gruenbacher <agruen@kernel.org>

    Doing a chmod() sets the file mode, which includes the file permission
    bits. When a file has a richacl, the permissions that the richacl
    grants need to be limited to what the new file permission bits allow.

    This is done by setting the file masks in the richacl to what the file
    permission bits map to. The richacl access check algorithm takes the
    file masks into account, which ensures that the richacl cannot grant too
    many permissions.

    It is possible to explicitly add permissions to the file masks which go
    beyond what the file permission bits can grant (like the ACE4_WRITE_ACL
    permission). The POSIX.1 standard calls this an alternate file access
    control mechanism. A subsequent chmod() would ensure that those
    permissions are disabled again.

    Acked-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    fs/richacl_base.c | 40 ++++++++++++++++++++++++++++++++++++++++
    include/linux/richacl.h | 1 +
    2 files changed, 41 insertions(+), 0 deletions(-)

    diff --git a/fs/richacl_base.c b/fs/richacl_base.c
    index a0197ed..a5f215e 100644
    --- a/fs/richacl_base.c
    +++ b/fs/richacl_base.c
    @@ -352,3 +352,43 @@ restart:
    acl->a_flags &= ~ACL4_MASKED;
    }
    EXPORT_SYMBOL_GPL(richacl_compute_max_masks);
    +
    +/**
    + * richacl_chmod - update the file masks to reflect the new mode
    + * @mode: new file permission bits
    + *
    + * Return a copy of @acl where the file masks have been replaced by the file
    + * masks corresponding to the file permission bits in @mode, or returns @acl
    + * itself if the file masks are already up to date. Takes over a reference
    + * to @acl.
    + */
    +struct richacl *
    +richacl_chmod(struct richacl *acl, mode_t mode)
    +{
    + unsigned int owner_mask, group_mask, other_mask;
    + struct richacl *clone;
    +
    + owner_mask = richacl_mode_to_mask(mode >> 6) |
    + ACE4_POSIX_OWNER_ALLOWED;
    + group_mask = richacl_mode_to_mask(mode >> 3);
    + other_mask = richacl_mode_to_mask(mode);
    +
    + if (acl->a_owner_mask == owner_mask &&
    + acl->a_group_mask == group_mask &&
    + acl->a_other_mask == other_mask &&
    + (acl->a_flags & ACL4_MASKED))
    + return acl;
    +
    + clone = richacl_clone(acl);
    + richacl_put(acl);
    + if (!clone)
    + return ERR_PTR(-ENOMEM);
    +
    + clone->a_flags |= ACL4_MASKED;
    + clone->a_owner_mask = owner_mask;
    + clone->a_group_mask = group_mask;
    + clone->a_other_mask = other_mask;
    +
    + return clone;
    +}
    +EXPORT_SYMBOL_GPL(richacl_chmod);
    diff --git a/include/linux/richacl.h b/include/linux/richacl.h
    index ded57e9..be7db1f 100644
    --- a/include/linux/richacl.h
    +++ b/include/linux/richacl.h
    @@ -288,5 +288,6 @@ extern int richacl_masks_to_mode(const struct richacl *);
    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 *);
    +extern struct richacl *richacl_chmod(struct richacl *, mode_t);

    #endif /* __RICHACL_H */
    --
    1.7.5.4


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