fs/9p/fid.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * V9FS FID Management
   4  *
   5  *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
   6  *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/errno.h>
  11 #include <linux/fs.h>
  12 #include <linux/slab.h>
  13 #include <linux/sched.h>
  14 #include <linux/idr.h>
  15 #include <net/9p/9p.h>
  16 #include <net/9p/client.h>
  17
  18 #include "v9fs.h"
  19 #include "v9fs_vfs.h"
  20 #include "fid.h"
  21
  22 /**
  23  * v9fs_fid_add - add a fid to a dentry
  24  * @dentry: dentry that the fid is being added to
  25  * @fid: fid to add
  26  *
  27  */
  28
  29 static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
  30 {
  31         hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
  32 }
  33
  34 void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
  35 {
  36         spin_lock(&dentry->d_lock);
  37         __add_fid(dentry, fid);
  38         spin_unlock(&dentry->d_lock);
  39 }
  40
  41 /**
  42  * v9fs_fid_find - retrieve a fid that belongs to the specified uid
  43  * @dentry: dentry to look for fid in
  44  * @uid: return fid that belongs to the specified user
  45  * @any: if non-zero, return any fid associated with the dentry
  46  *
  47  */
  48
  49 static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
  50 {
  51         struct p9_fid *fid, *ret;
  52
  53         p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p) uid %d any %d\n",
  54                  dentry, dentry, from_kuid(&init_user_ns, uid),
  55                  any);
  56         ret = NULL;
  57         /* we'll recheck under lock if there's anything to look in */
  58         if (dentry->d_fsdata) {
  59                 struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
  60                 spin_lock(&dentry->d_lock);
  61                 hlist_for_each_entry(fid, h, dlist) {
  62                         if (any || uid_eq(fid->uid, uid)) {
  63                                 ret = fid;
  64                                 break;
  65                         }
  66                 }
  67                 spin_unlock(&dentry->d_lock);
  68         }
  69
  70         return ret;
  71 }
  72
  73 /*
  74  * We need to hold v9ses->rename_sem as long as we hold references
  75  * to returned path array. Array element contain pointers to
  76  * dentry names.
  77  */
  78 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
  79                                   struct dentry *dentry, const unsigned char ***names)
  80 {
  81         int n = 0, i;
  82         const unsigned char **wnames;
  83         struct dentry *ds;
  84
  85         for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
  86                 n++;
  87
  88         wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
  89         if (!wnames)
  90                 goto err_out;
  91
  92         for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
  93                 wnames[i] = ds->d_name.name;
  94
  95         *names = wnames;
  96         return n;
  97 err_out:
  98         return -ENOMEM;
  99 }
 100
 101 static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 102                                                kuid_t uid, int any)
 103 {
 104         struct dentry *ds;
 105         const unsigned char **wnames, *uname;
 106         int i, n, l, clone, access;
 107         struct v9fs_session_info *v9ses;
 108         struct p9_fid *fid, *old_fid = NULL;
 109
 110         v9ses = v9fs_dentry2v9ses(dentry);
 111         access = v9ses->flags & V9FS_ACCESS_MASK;
 112         fid = v9fs_fid_find(dentry, uid, any);
 113         if (fid)
 114                 return fid;
 115         /*
 116          * we don't have a matching fid. To do a TWALK we need
 117          * parent fid. We need to prevent rename when we want to
 118          * look at the parent.
 119          */
 120         down_read(&v9ses->rename_sem);
 121         ds = dentry->d_parent;
 122         fid = v9fs_fid_find(ds, uid, any);
 123         if (fid) {
 124                 /* Found the parent fid do a lookup with that */
 125                 fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
 126                 goto fid_out;
 127         }
 128         up_read(&v9ses->rename_sem);
 129
 130         /* start from the root and try to do a lookup */
 131         fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
 132         if (!fid) {
 133                 /* the user is not attached to the fs yet */
 134                 if (access == V9FS_ACCESS_SINGLE)
 135                         return ERR_PTR(-EPERM);
 136
 137                 if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
 138                                 uname = NULL;
 139                 else
 140                         uname = v9ses->uname;
 141
 142                 fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
 143                                        v9ses->aname);
 144                 if (IS_ERR(fid))
 145                         return fid;
 146
 147                 v9fs_fid_add(dentry->d_sb->s_root, fid);
 148         }
 149         /* If we are root ourself just return that */
 150         if (dentry->d_sb->s_root == dentry)
 151                 return fid;
 152         /*
 153          * Do a multipath walk with attached root.
 154          * When walking parent we need to make sure we
 155          * don't have a parallel rename happening
 156          */
 157         down_read(&v9ses->rename_sem);
 158         n  = build_path_from_dentry(v9ses, dentry, &wnames);
 159         if (n < 0) {
 160                 fid = ERR_PTR(n);
 161                 goto err_out;
 162         }
 163         clone = 1;
 164         i = 0;
 165         while (i < n) {
 166                 l = min(n - i, P9_MAXWELEM);
 167                 /*
 168                  * We need to hold rename lock when doing a multipath
 169                  * walk to ensure none of the patch component change
 170                  */
 171                 fid = p9_client_walk(fid, l, &wnames[i], clone);
 172                 if (IS_ERR(fid)) {
 173                         if (old_fid) {
 174                                 /*
 175                                  * If we fail, clunk fid which are mapping
 176                                  * to path component and not the last component
 177                                  * of the path.
 178                                  */
 179                                 p9_client_clunk(old_fid);
 180                         }
 181                         kfree(wnames);
 182                         goto err_out;
 183                 }
 184                 old_fid = fid;
 185                 i += l;
 186                 clone = 0;
 187         }
 188         kfree(wnames);
 189 fid_out:
 190         if (!IS_ERR(fid)) {
 191                 spin_lock(&dentry->d_lock);
 192                 if (d_unhashed(dentry)) {
 193                         spin_unlock(&dentry->d_lock);
 194                         p9_client_clunk(fid);
 195                         fid = ERR_PTR(-ENOENT);
 196                 } else {
 197                         __add_fid(dentry, fid);
 198                         spin_unlock(&dentry->d_lock);
 199                 }
 200         }
 201 err_out:
 202         up_read(&v9ses->rename_sem);
 203         return fid;
 204 }
 205
 206 /**
 207  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 208  * @dentry: dentry to look for fid in
 209  *
 210  * Look for a fid in the specified dentry for the current user.
 211  * If no fid is found, try to create one walking from a fid from the parent
 212  * dentry (if it has one), or the root dentry. If the user haven't accessed
 213  * the fs yet, attach now and walk from the root.
 214  */
 215
 216 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 217 {
 218         kuid_t uid;
 219         int  any, access;
 220         struct v9fs_session_info *v9ses;
 221
 222         v9ses = v9fs_dentry2v9ses(dentry);
 223         access = v9ses->flags & V9FS_ACCESS_MASK;
 224         switch (access) {
 225         case V9FS_ACCESS_SINGLE:
 226         case V9FS_ACCESS_USER:
 227         case V9FS_ACCESS_CLIENT:
 228                 uid = current_fsuid();
 229                 any = 0;
 230                 break;
 231
 232         case V9FS_ACCESS_ANY:
 233                 uid = v9ses->uid;
 234                 any = 1;
 235                 break;
 236
 237         default:
 238                 uid = INVALID_UID;
 239                 any = 0;
 240                 break;
 241         }
 242         return v9fs_fid_lookup_with_uid(dentry, uid, any);
 243 }
 244
 245 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
 246 {
 247         int err;
 248         struct p9_fid *fid;
 249
 250         fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
 251         if (IS_ERR(fid))
 252                 goto error_out;
 253         /*
 254          * writeback fid will only be used to write back the
 255          * dirty pages. We always request for the open fid in read-write
 256          * mode so that a partial page write which result in page
 257          * read can work.
 258          */
 259         err = p9_client_open(fid, O_RDWR);
 260         if (err < 0) {
 261                 p9_client_clunk(fid);
 262                 fid = ERR_PTR(err);
 263                 goto error_out;
 264         }
 265 error_out:
 266         return fid;
 267 }