nfsacl.c

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/*
 * fs/nfs_common/nfsacl.c
 *
 *  Copyright (C) 2002-2003 Andreas Gruenbacher <[email protected]>
 */

/*
 * The Solaris nfsacl protocol represents some ACLs slightly differently
 * than POSIX 1003.1e draft 17 does (and we do):
 *
 *  - Minimal ACLs always have an ACL_MASK entry, so they have
 *    four instead of three entries.
 *  - The ACL_MASK entry in such minimal ACLs always has the same
 *    permissions as the ACL_GROUP_OBJ entry. (In extended ACLs
 *    the ACL_MASK and ACL_GROUP_OBJ entries may differ.)
 *  - The identifier fields of the ACL_USER_OBJ and ACL_GROUP_OBJ
 *    entries contain the identifiers of the owner and owning group.
 *    (In POSIX ACLs we always set them to ACL_UNDEFINED_ID).
 *  - ACL entries in the kernel are kept sorted in ascending order
 *    of (e_tag, e_id). Solaris ACLs are unsorted.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/sunrpc/xdr.h>
#include <linux/nfsacl.h>
#include <linux/nfs3.h>
#include <linux/sort.h>

MODULE_LICENSE("GPL");

EXPORT_SYMBOL_GPL(nfsacl_encode);
EXPORT_SYMBOL_GPL(nfsacl_decode);

struct nfsacl_encode_desc {
    struct xdr_array2_desc desc;
    unsigned int count;
    struct posix_acl *acl;
    int typeflag;
    uid_t uid;
    gid_t gid;
};

struct nfsacl_simple_acl {
    struct posix_acl acl;
    struct posix_acl_entry ace[4];
};

static int
xdr_nfsace_encode(struct xdr_array2_desc *desc, void *elem)
{
    struct nfsacl_encode_desc *nfsacl_desc =
        (struct nfsacl_encode_desc *) desc;
    __be32 *p = elem;

    struct posix_acl_entry *entry =
        &nfsacl_desc->acl->a_entries[nfsacl_desc->count++];

    *p++ = htonl(entry->e_tag | nfsacl_desc->typeflag);
    switch(entry->e_tag) {
        case ACL_USER_OBJ:
            *p++ = htonl(nfsacl_desc->uid);
            break;
        case ACL_GROUP_OBJ:
            *p++ = htonl(nfsacl_desc->gid);
            break;
        case ACL_USER:
        case ACL_GROUP:
            *p++ = htonl(entry->e_id);
            break;
        default:  /* Solaris depends on that! */
            *p++ = 0;
            break;
    }
    *p++ = htonl(entry->e_perm & S_IRWXO);
    return 0;
}

int nfsacl_encode(struct xdr_buf *buf, unsigned int base, struct inode *inode,
          struct posix_acl *acl, int encode_entries, int typeflag)
{
    int entries = (acl && acl->a_count) ? max_t(int, acl->a_count, 4) : 0;
    struct nfsacl_encode_desc nfsacl_desc = {
        .desc = {
            .elem_size = 12,
            .array_len = encode_entries ? entries : 0,
            .xcode = xdr_nfsace_encode,
        },
        .acl = acl,
        .typeflag = typeflag,
        .uid = inode->i_uid,
        .gid = inode->i_gid,
    };
    struct nfsacl_simple_acl aclbuf;
    int err;

    if (entries > NFS_ACL_MAX_ENTRIES ||
        xdr_encode_word(buf, base, entries))
        return -EINVAL;
    if (encode_entries && acl && acl->a_count == 3) {
        struct posix_acl *acl2 = &aclbuf.acl;

        /* Avoid the use of posix_acl_alloc().  nfsacl_encode() is
         * invoked in contexts where a memory allocation failure is
         * fatal.  Fortunately this fake ACL is small enough to
         * construct on the stack. */
        posix_acl_init(acl2, 4);

        /* Insert entries in canonical order: other orders seem
         to confuse Solaris VxFS. */
        acl2->a_entries[0] = acl->a_entries[0];  /* ACL_USER_OBJ */
        acl2->a_entries[1] = acl->a_entries[1];  /* ACL_GROUP_OBJ */
        acl2->a_entries[2] = acl->a_entries[1];  /* ACL_MASK */
        acl2->a_entries[2].e_tag = ACL_MASK;
        acl2->a_entries[3] = acl->a_entries[2];  /* ACL_OTHER */
        nfsacl_desc.acl = acl2;
    }
    err = xdr_encode_array2(buf, base + 4, &nfsacl_desc.desc);
    if (!err)
        err = 8 + nfsacl_desc.desc.elem_size *
              nfsacl_desc.desc.array_len;
    return err;
}

struct nfsacl_decode_desc {
    struct xdr_array2_desc desc;
    unsigned int count;
    struct posix_acl *acl;
};

static int
xdr_nfsace_decode(struct xdr_array2_desc *desc, void *elem)
{
    struct nfsacl_decode_desc *nfsacl_desc =
        (struct nfsacl_decode_desc *) desc;
    __be32 *p = elem;
    struct posix_acl_entry *entry;

    if (!nfsacl_desc->acl) {
        if (desc->array_len > NFS_ACL_MAX_ENTRIES)
            return -EINVAL;
        nfsacl_desc->acl = posix_acl_alloc(desc->array_len, GFP_KERNEL);
        if (!nfsacl_desc->acl)
            return -ENOMEM;
        nfsacl_desc->count = 0;
    }

    entry = &nfsacl_desc->acl->a_entries[nfsacl_desc->count++];
    entry->e_tag = ntohl(*p++) & ~NFS_ACL_DEFAULT;
    entry->e_id = ntohl(*p++);
    entry->e_perm = ntohl(*p++);

    switch(entry->e_tag) {
        case ACL_USER_OBJ:
        case ACL_USER:
        case ACL_GROUP_OBJ:
        case ACL_GROUP:
        case ACL_OTHER:
            if (entry->e_perm & ~S_IRWXO)
                return -EINVAL;
            break;
        case ACL_MASK:
            /* Solaris sometimes sets additional bits in the mask */
            entry->e_perm &= S_IRWXO;
            break;
        default:
            return -EINVAL;
    }

    return 0;
}

static int
cmp_acl_entry(const void *x, const void *y)
{
    const struct posix_acl_entry *a = x, *b = y;

    if (a->e_tag != b->e_tag)
        return a->e_tag - b->e_tag;
    else if (a->e_id > b->e_id)
        return 1;
    else if (a->e_id < b->e_id)
        return -1;
    else
        return 0;
}

/*
 * Convert from a Solaris ACL to a POSIX 1003.1e draft 17 ACL.
 */
static int
posix_acl_from_nfsacl(struct posix_acl *acl)
{
    struct posix_acl_entry *pa, *pe,
           *group_obj = NULL, *mask = NULL;

    if (!acl)
        return 0;

    sort(acl->a_entries, acl->a_count, sizeof(struct posix_acl_entry),
         cmp_acl_entry, NULL);

    /* Clear undefined identifier fields and find the ACL_GROUP_OBJ
       and ACL_MASK entries. */
    FOREACH_ACL_ENTRY(pa, acl, pe) {
        switch(pa->e_tag) {
            case ACL_USER_OBJ:
                pa->e_id = ACL_UNDEFINED_ID;
                break;
            case ACL_GROUP_OBJ:
                pa->e_id = ACL_UNDEFINED_ID;
                group_obj = pa;
                break;
            case ACL_MASK:
                mask = pa;
                /* fall through */
            case ACL_OTHER:
                pa->e_id = ACL_UNDEFINED_ID;
                break;
        }
    }
    if (acl->a_count == 4 && group_obj && mask &&
        mask->e_perm == group_obj->e_perm) {
        /* remove bogus ACL_MASK entry */
        memmove(mask, mask+1, (3 - (mask - acl->a_entries)) *
                      sizeof(struct posix_acl_entry));
        acl->a_count = 3;
    }
    return 0;
}

int nfsacl_decode(struct xdr_buf *buf, unsigned int base, unsigned int *aclcnt,
          struct posix_acl **pacl)
{
    struct nfsacl_decode_desc nfsacl_desc = {
        .desc = {
            .elem_size = 12,
            .xcode = pacl ? xdr_nfsace_decode : NULL,
        },
    };
    u32 entries;
    int err;

    if (xdr_decode_word(buf, base, &entries) ||
        entries > NFS_ACL_MAX_ENTRIES)
        return -EINVAL;
    nfsacl_desc.desc.array_maxlen = entries;
    err = xdr_decode_array2(buf, base + 4, &nfsacl_desc.desc);
    if (err)
        return err;
    if (pacl) {
        if (entries != nfsacl_desc.desc.array_len ||
            posix_acl_from_nfsacl(nfsacl_desc.acl) != 0) {
            posix_acl_release(nfsacl_desc.acl);
            return -EINVAL;
        }
        *pacl = nfsacl_desc.acl;
    }
    if (aclcnt)
        *aclcnt = entries;
    return 8 + nfsacl_desc.desc.elem_size *
           nfsacl_desc.desc.array_len;
}