fs/quota/quota.c

   1 /*
   2  * Quota code necessary even when VFS quota support is not compiled
   3  * into the kernel.  The interesting stuff is over in dquot.c, here
   4  * we have symbols for initial quotactl(2) handling, the sysctl(2)
   5  * variables, etc - things needed even when quota support disabled.
   6  */
   7
   8 #include <linux/fs.h>
   9 #include <linux/namei.h>
  10 #include <linux/slab.h>
  11 #include <asm/current.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/kernel.h>
  14 #include <linux/security.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/capability.h>
  17 #include <linux/quotaops.h>
  18 #include <linux/types.h>
  19 #include <linux/writeback.h>
  20
  21 static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
  22                                      qid_t id)
  23 {
  24         switch (cmd) {
  25         /* these commands do not require any special privilegues */
  26         case Q_GETFMT:
  27         case Q_SYNC:
  28         case Q_GETINFO:
  29         case Q_XGETQSTAT:
  30         case Q_XGETQSTATV:
  31         case Q_XQUOTASYNC:
  32                 break;
  33         /* allow to query information for dquots we "own" */
  34         case Q_GETQUOTA:
  35         case Q_XGETQUOTA:
  36                 if ((type == USRQUOTA && uid_eq(current_euid(), make_kuid(current_user_ns(), id))) ||
  37                     (type == GRPQUOTA && in_egroup_p(make_kgid(current_user_ns(), id))))
  38                         break;
  39                 /*FALLTHROUGH*/
  40         default:
  41                 if (!capable(CAP_SYS_ADMIN))
  42                         return -EPERM;
  43         }
  44
  45         return security_quotactl(cmd, type, id, sb);
  46 }
  47
  48 static void quota_sync_one(struct super_block *sb, void *arg)
  49 {
  50         int type = *(int *)arg;
  51
  52         if (sb->s_qcop && sb->s_qcop->quota_sync &&
  53             (sb->s_quota_types & (1 << type)))
  54                 sb->s_qcop->quota_sync(sb, type);
  55 }
  56
  57 static int quota_sync_all(int type)
  58 {
  59         int ret;
  60
  61         if (type >= MAXQUOTAS)
  62                 return -EINVAL;
  63         ret = security_quotactl(Q_SYNC, type, 0, NULL);
  64         if (!ret)
  65                 iterate_supers(quota_sync_one, &type);
  66         return ret;
  67 }
  68
  69 unsigned int qtype_enforce_flag(int type)
  70 {
  71         switch (type) {
  72         case USRQUOTA:
  73                 return FS_QUOTA_UDQ_ENFD;
  74         case GRPQUOTA:
  75                 return FS_QUOTA_GDQ_ENFD;
  76         case PRJQUOTA:
  77                 return FS_QUOTA_PDQ_ENFD;
  78         }
  79         return 0;
  80 }
  81
  82 static int quota_quotaon(struct super_block *sb, int type, int cmd, qid_t id,
  83                          struct path *path)
  84 {
  85         if (!sb->s_qcop->quota_on && !sb->s_qcop->quota_enable)
  86                 return -ENOSYS;
  87         if (sb->s_qcop->quota_enable)
  88                 return sb->s_qcop->quota_enable(sb, qtype_enforce_flag(type));
  89         if (IS_ERR(path))
  90                 return PTR_ERR(path);
  91         return sb->s_qcop->quota_on(sb, type, id, path);
  92 }
  93
  94 static int quota_quotaoff(struct super_block *sb, int type)
  95 {
  96         if (!sb->s_qcop->quota_off && !sb->s_qcop->quota_disable)
  97                 return -ENOSYS;
  98         if (sb->s_qcop->quota_disable)
  99                 return sb->s_qcop->quota_disable(sb, qtype_enforce_flag(type));
 100         return sb->s_qcop->quota_off(sb, type);
 101 }
 102
 103 static int quota_getfmt(struct super_block *sb, int type, void __user *addr)
 104 {
 105         __u32 fmt;
 106
 107         mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
 108         if (!sb_has_quota_active(sb, type)) {
 109                 mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
 110                 return -ESRCH;
 111         }
 112         fmt = sb_dqopt(sb)->info[type].dqi_format->qf_fmt_id;
 113         mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
 114         if (copy_to_user(addr, &fmt, sizeof(fmt)))
 115                 return -EFAULT;
 116         return 0;
 117 }
 118
 119 static int quota_getinfo(struct super_block *sb, int type, void __user *addr)
 120 {
 121         struct if_dqinfo info;
 122         int ret;
 123
 124         if (!sb->s_qcop->get_info)
 125                 return -ENOSYS;
 126         ret = sb->s_qcop->get_info(sb, type, &info);
 127         if (!ret && copy_to_user(addr, &info, sizeof(info)))
 128                 return -EFAULT;
 129         return ret;
 130 }
 131
 132 static int quota_setinfo(struct super_block *sb, int type, void __user *addr)
 133 {
 134         struct if_dqinfo info;
 135
 136         if (copy_from_user(&info, addr, sizeof(info)))
 137                 return -EFAULT;
 138         if (!sb->s_qcop->set_info)
 139                 return -ENOSYS;
 140         return sb->s_qcop->set_info(sb, type, &info);
 141 }
 142
 143 static inline qsize_t qbtos(qsize_t blocks)
 144 {
 145         return blocks << QIF_DQBLKSIZE_BITS;
 146 }
 147
 148 static inline qsize_t stoqb(qsize_t space)
 149 {
 150         return (space + QIF_DQBLKSIZE - 1) >> QIF_DQBLKSIZE_BITS;
 151 }
 152
 153 static void copy_to_if_dqblk(struct if_dqblk *dst, struct qc_dqblk *src)
 154 {
 155         memset(dst, 0, sizeof(*dst));
 156         dst->dqb_bhardlimit = stoqb(src->d_spc_hardlimit);
 157         dst->dqb_bsoftlimit = stoqb(src->d_spc_softlimit);
 158         dst->dqb_curspace = src->d_space;
 159         dst->dqb_ihardlimit = src->d_ino_hardlimit;
 160         dst->dqb_isoftlimit = src->d_ino_softlimit;
 161         dst->dqb_curinodes = src->d_ino_count;
 162         dst->dqb_btime = src->d_spc_timer;
 163         dst->dqb_itime = src->d_ino_timer;
 164         dst->dqb_valid = QIF_ALL;
 165 }
 166
 167 static int quota_getquota(struct super_block *sb, int type, qid_t id,
 168                           void __user *addr)
 169 {
 170         struct kqid qid;
 171         struct qc_dqblk fdq;
 172         struct if_dqblk idq;
 173         int ret;
 174
 175         if (!sb->s_qcop->get_dqblk)
 176                 return -ENOSYS;
 177         qid = make_kqid(current_user_ns(), type, id);
 178         if (!qid_valid(qid))
 179                 return -EINVAL;
 180         ret = sb->s_qcop->get_dqblk(sb, qid, &fdq);
 181         if (ret)
 182                 return ret;
 183         copy_to_if_dqblk(&idq, &fdq);
 184         if (copy_to_user(addr, &idq, sizeof(idq)))
 185                 return -EFAULT;
 186         return 0;
 187 }
 188
 189 static void copy_from_if_dqblk(struct qc_dqblk *dst, struct if_dqblk *src)
 190 {
 191         dst->d_spc_hardlimit = qbtos(src->dqb_bhardlimit);
 192         dst->d_spc_softlimit = qbtos(src->dqb_bsoftlimit);
 193         dst->d_space = src->dqb_curspace;
 194         dst->d_ino_hardlimit = src->dqb_ihardlimit;
 195         dst->d_ino_softlimit = src->dqb_isoftlimit;
 196         dst->d_ino_count = src->dqb_curinodes;
 197         dst->d_spc_timer = src->dqb_btime;
 198         dst->d_ino_timer = src->dqb_itime;
 199
 200         dst->d_fieldmask = 0;
 201         if (src->dqb_valid & QIF_BLIMITS)
 202                 dst->d_fieldmask |= QC_SPC_SOFT | QC_SPC_HARD;
 203         if (src->dqb_valid & QIF_SPACE)
 204                 dst->d_fieldmask |= QC_SPACE;
 205         if (src->dqb_valid & QIF_ILIMITS)
 206                 dst->d_fieldmask |= QC_INO_SOFT | QC_INO_HARD;
 207         if (src->dqb_valid & QIF_INODES)
 208                 dst->d_fieldmask |= QC_INO_COUNT;
 209         if (src->dqb_valid & QIF_BTIME)
 210                 dst->d_fieldmask |= QC_SPC_TIMER;
 211         if (src->dqb_valid & QIF_ITIME)
 212                 dst->d_fieldmask |= QC_INO_TIMER;
 213 }
 214
 215 static int quota_setquota(struct super_block *sb, int type, qid_t id,
 216                           void __user *addr)
 217 {
 218         struct qc_dqblk fdq;
 219         struct if_dqblk idq;
 220         struct kqid qid;
 221
 222         if (copy_from_user(&idq, addr, sizeof(idq)))
 223                 return -EFAULT;
 224         if (!sb->s_qcop->set_dqblk)
 225                 return -ENOSYS;
 226         qid = make_kqid(current_user_ns(), type, id);
 227         if (!qid_valid(qid))
 228                 return -EINVAL;
 229         copy_from_if_dqblk(&fdq, &idq);
 230         return sb->s_qcop->set_dqblk(sb, qid, &fdq);
 231 }
 232
 233 static int quota_enable(struct super_block *sb, void __user *addr)
 234 {
 235         __u32 flags;
 236
 237         if (copy_from_user(&flags, addr, sizeof(flags)))
 238                 return -EFAULT;
 239         if (!sb->s_qcop->quota_enable)
 240                 return -ENOSYS;
 241         return sb->s_qcop->quota_enable(sb, flags);
 242 }
 243
 244 static int quota_disable(struct super_block *sb, void __user *addr)
 245 {
 246         __u32 flags;
 247
 248         if (copy_from_user(&flags, addr, sizeof(flags)))
 249                 return -EFAULT;
 250         if (!sb->s_qcop->quota_disable)
 251                 return -ENOSYS;
 252         return sb->s_qcop->quota_disable(sb, flags);
 253 }
 254
 255 static int quota_getxstate(struct super_block *sb, void __user *addr)
 256 {
 257         struct fs_quota_stat fqs;
 258         int ret;
 259
 260         if (!sb->s_qcop->get_xstate)
 261                 return -ENOSYS;
 262         ret = sb->s_qcop->get_xstate(sb, &fqs);
 263         if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
 264                 return -EFAULT;
 265         return ret;
 266 }
 267
 268 static int quota_getxstatev(struct super_block *sb, void __user *addr)
 269 {
 270         struct fs_quota_statv fqs;
 271         int ret;
 272
 273         if (!sb->s_qcop->get_xstatev)
 274                 return -ENOSYS;
 275
 276         memset(&fqs, 0, sizeof(fqs));
 277         if (copy_from_user(&fqs, addr, 1)) /* Just read qs_version */
 278                 return -EFAULT;
 279
 280         /* If this kernel doesn't support user specified version, fail */
 281         switch (fqs.qs_version) {
 282         case FS_QSTATV_VERSION1:
 283                 break;
 284         default:
 285                 return -EINVAL;
 286         }
 287         ret = sb->s_qcop->get_xstatev(sb, &fqs);
 288         if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
 289                 return -EFAULT;
 290         return ret;
 291 }
 292
 293 /*
 294  * XFS defines BBTOB and BTOBB macros inside fs/xfs/ and we cannot move them
 295  * out of there as xfsprogs rely on definitions being in that header file. So
 296  * just define same functions here for quota purposes.
 297  */
 298 #define XFS_BB_SHIFT 9
 299
 300 static inline u64 quota_bbtob(u64 blocks)
 301 {
 302         return blocks << XFS_BB_SHIFT;
 303 }
 304
 305 static inline u64 quota_btobb(u64 bytes)
 306 {
 307         return (bytes + (1 << XFS_BB_SHIFT) - 1) >> XFS_BB_SHIFT;
 308 }
 309
 310 static void copy_from_xfs_dqblk(struct qc_dqblk *dst, struct fs_disk_quota *src)
 311 {
 312         dst->d_spc_hardlimit = quota_bbtob(src->d_blk_hardlimit);
 313         dst->d_spc_softlimit = quota_bbtob(src->d_blk_softlimit);
 314         dst->d_ino_hardlimit = src->d_ino_hardlimit;
 315         dst->d_ino_softlimit = src->d_ino_softlimit;
 316         dst->d_space = quota_bbtob(src->d_bcount);
 317         dst->d_ino_count = src->d_icount;
 318         dst->d_ino_timer = src->d_itimer;
 319         dst->d_spc_timer = src->d_btimer;
 320         dst->d_ino_warns = src->d_iwarns;
 321         dst->d_spc_warns = src->d_bwarns;
 322         dst->d_rt_spc_hardlimit = quota_bbtob(src->d_rtb_hardlimit);
 323         dst->d_rt_spc_softlimit = quota_bbtob(src->d_rtb_softlimit);
 324         dst->d_rt_space = quota_bbtob(src->d_rtbcount);
 325         dst->d_rt_spc_timer = src->d_rtbtimer;
 326         dst->d_rt_spc_warns = src->d_rtbwarns;
 327         dst->d_fieldmask = 0;
 328         if (src->d_fieldmask & FS_DQ_ISOFT)
 329                 dst->d_fieldmask |= QC_INO_SOFT;
 330         if (src->d_fieldmask & FS_DQ_IHARD)
 331                 dst->d_fieldmask |= QC_INO_HARD;
 332         if (src->d_fieldmask & FS_DQ_BSOFT)
 333                 dst->d_fieldmask |= QC_SPC_SOFT;
 334         if (src->d_fieldmask & FS_DQ_BHARD)
 335                 dst->d_fieldmask |= QC_SPC_HARD;
 336         if (src->d_fieldmask & FS_DQ_RTBSOFT)
 337                 dst->d_fieldmask |= QC_RT_SPC_SOFT;
 338         if (src->d_fieldmask & FS_DQ_RTBHARD)
 339                 dst->d_fieldmask |= QC_RT_SPC_HARD;
 340         if (src->d_fieldmask & FS_DQ_BTIMER)
 341                 dst->d_fieldmask |= QC_SPC_TIMER;
 342         if (src->d_fieldmask & FS_DQ_ITIMER)
 343                 dst->d_fieldmask |= QC_INO_TIMER;
 344         if (src->d_fieldmask & FS_DQ_RTBTIMER)
 345                 dst->d_fieldmask |= QC_RT_SPC_TIMER;
 346         if (src->d_fieldmask & FS_DQ_BWARNS)
 347                 dst->d_fieldmask |= QC_SPC_WARNS;
 348         if (src->d_fieldmask & FS_DQ_IWARNS)
 349                 dst->d_fieldmask |= QC_INO_WARNS;
 350         if (src->d_fieldmask & FS_DQ_RTBWARNS)
 351                 dst->d_fieldmask |= QC_RT_SPC_WARNS;
 352         if (src->d_fieldmask & FS_DQ_BCOUNT)
 353                 dst->d_fieldmask |= QC_SPACE;
 354         if (src->d_fieldmask & FS_DQ_ICOUNT)
 355                 dst->d_fieldmask |= QC_INO_COUNT;
 356         if (src->d_fieldmask & FS_DQ_RTBCOUNT)
 357                 dst->d_fieldmask |= QC_RT_SPACE;
 358 }
 359
 360 static int quota_setxquota(struct super_block *sb, int type, qid_t id,
 361                            void __user *addr)
 362 {
 363         struct fs_disk_quota fdq;
 364         struct qc_dqblk qdq;
 365         struct kqid qid;
 366
 367         if (copy_from_user(&fdq, addr, sizeof(fdq)))
 368                 return -EFAULT;
 369         if (!sb->s_qcop->set_dqblk)
 370                 return -ENOSYS;
 371         qid = make_kqid(current_user_ns(), type, id);
 372         if (!qid_valid(qid))
 373                 return -EINVAL;
 374         copy_from_xfs_dqblk(&qdq, &fdq);
 375         return sb->s_qcop->set_dqblk(sb, qid, &qdq);
 376 }
 377
 378 static void copy_to_xfs_dqblk(struct fs_disk_quota *dst, struct qc_dqblk *src,
 379                               int type, qid_t id)
 380 {
 381         memset(dst, 0, sizeof(*dst));
 382         dst->d_version = FS_DQUOT_VERSION;
 383         dst->d_id = id;
 384         if (type == USRQUOTA)
 385                 dst->d_flags = FS_USER_QUOTA;
 386         else if (type == PRJQUOTA)
 387                 dst->d_flags = FS_PROJ_QUOTA;
 388         else
 389                 dst->d_flags = FS_GROUP_QUOTA;
 390         dst->d_blk_hardlimit = quota_btobb(src->d_spc_hardlimit);
 391         dst->d_blk_softlimit = quota_btobb(src->d_spc_softlimit);
 392         dst->d_ino_hardlimit = src->d_ino_hardlimit;
 393         dst->d_ino_softlimit = src->d_ino_softlimit;
 394         dst->d_bcount = quota_btobb(src->d_space);
 395         dst->d_icount = src->d_ino_count;
 396         dst->d_itimer = src->d_ino_timer;
 397         dst->d_btimer = src->d_spc_timer;
 398         dst->d_iwarns = src->d_ino_warns;
 399         dst->d_bwarns = src->d_spc_warns;
 400         dst->d_rtb_hardlimit = quota_btobb(src->d_rt_spc_hardlimit);
 401         dst->d_rtb_softlimit = quota_btobb(src->d_rt_spc_softlimit);
 402         dst->d_rtbcount = quota_btobb(src->d_rt_space);
 403         dst->d_rtbtimer = src->d_rt_spc_timer;
 404         dst->d_rtbwarns = src->d_rt_spc_warns;
 405 }
 406
 407 static int quota_getxquota(struct super_block *sb, int type, qid_t id,
 408                            void __user *addr)
 409 {
 410         struct fs_disk_quota fdq;
 411         struct qc_dqblk qdq;
 412         struct kqid qid;
 413         int ret;
 414
 415         if (!sb->s_qcop->get_dqblk)
 416                 return -ENOSYS;
 417         qid = make_kqid(current_user_ns(), type, id);
 418         if (!qid_valid(qid))
 419                 return -EINVAL;
 420         ret = sb->s_qcop->get_dqblk(sb, qid, &qdq);
 421         if (ret)
 422                 return ret;
 423         copy_to_xfs_dqblk(&fdq, &qdq, type, id);
 424         if (copy_to_user(addr, &fdq, sizeof(fdq)))
 425                 return -EFAULT;
 426         return ret;
 427 }
 428
 429 static int quota_rmxquota(struct super_block *sb, void __user *addr)
 430 {
 431         __u32 flags;
 432
 433         if (copy_from_user(&flags, addr, sizeof(flags)))
 434                 return -EFAULT;
 435         if (!sb->s_qcop->rm_xquota)
 436                 return -ENOSYS;
 437         return sb->s_qcop->rm_xquota(sb, flags);
 438 }
 439
 440 /* Copy parameters and call proper function */
 441 static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
 442                        void __user *addr, struct path *path)
 443 {
 444         int ret;
 445
 446         if (type >= (XQM_COMMAND(cmd) ? XQM_MAXQUOTAS : MAXQUOTAS))
 447                 return -EINVAL;
 448         /*
 449          * Quota not supported on this fs? Check this before s_quota_types
 450          * since they needn't be set if quota is not supported at all.
 451          */
 452         if (!sb->s_qcop)
 453                 return -ENOSYS;
 454         if (!(sb->s_quota_types & (1 << type)))
 455                 return -EINVAL;
 456
 457         ret = check_quotactl_permission(sb, type, cmd, id);
 458         if (ret < 0)
 459                 return ret;
 460
 461         switch (cmd) {
 462         case Q_QUOTAON:
 463                 return quota_quotaon(sb, type, cmd, id, path);
 464         case Q_QUOTAOFF:
 465                 return quota_quotaoff(sb, type);
 466         case Q_GETFMT:
 467                 return quota_getfmt(sb, type, addr);
 468         case Q_GETINFO:
 469                 return quota_getinfo(sb, type, addr);
 470         case Q_SETINFO:
 471                 return quota_setinfo(sb, type, addr);
 472         case Q_GETQUOTA:
 473                 return quota_getquota(sb, type, id, addr);
 474         case Q_SETQUOTA:
 475                 return quota_setquota(sb, type, id, addr);
 476         case Q_SYNC:
 477                 if (!sb->s_qcop->quota_sync)
 478                         return -ENOSYS;
 479                 return sb->s_qcop->quota_sync(sb, type);
 480         case Q_XQUOTAON:
 481                 return quota_enable(sb, addr);
 482         case Q_XQUOTAOFF:
 483                 return quota_disable(sb, addr);
 484         case Q_XQUOTARM:
 485                 return quota_rmxquota(sb, addr);
 486         case Q_XGETQSTAT:
 487                 return quota_getxstate(sb, addr);
 488         case Q_XGETQSTATV:
 489                 return quota_getxstatev(sb, addr);
 490         case Q_XSETQLIM:
 491                 return quota_setxquota(sb, type, id, addr);
 492         case Q_XGETQUOTA:
 493                 return quota_getxquota(sb, type, id, addr);
 494         case Q_XQUOTASYNC:
 495                 if (sb->s_flags & MS_RDONLY)
 496                         return -EROFS;
 497                 /* XFS quotas are fully coherent now, making this call a noop */
 498                 return 0;
 499         default:
 500                 return -EINVAL;
 501         }
 502 }
 503
 504 #ifdef CONFIG_BLOCK
 505
 506 /* Return 1 if 'cmd' will block on frozen filesystem */
 507 static int quotactl_cmd_write(int cmd)
 508 {
 509         switch (cmd) {
 510         case Q_GETFMT:
 511         case Q_GETINFO:
 512         case Q_SYNC:
 513         case Q_XGETQSTAT:
 514         case Q_XGETQSTATV:
 515         case Q_XGETQUOTA:
 516         case Q_XQUOTASYNC:
 517                 return 0;
 518         }
 519         return 1;
 520 }
 521
 522 #endif /* CONFIG_BLOCK */
 523
 524 /*
 525  * look up a superblock on which quota ops will be performed
 526  * - use the name of a block device to find the superblock thereon
 527  */
 528 static struct super_block *quotactl_block(const char __user *special, int cmd)
 529 {
 530 #ifdef CONFIG_BLOCK
 531         struct block_device *bdev;
 532         struct super_block *sb;
 533         struct filename *tmp = getname(special);
 534
 535         if (IS_ERR(tmp))
 536                 return ERR_CAST(tmp);
 537         bdev = lookup_bdev(tmp->name);
 538         putname(tmp);
 539         if (IS_ERR(bdev))
 540                 return ERR_CAST(bdev);
 541         if (quotactl_cmd_write(cmd))
 542                 sb = get_super_thawed(bdev);
 543         else
 544                 sb = get_super(bdev);
 545         bdput(bdev);
 546         if (!sb)
 547                 return ERR_PTR(-ENODEV);
 548
 549         return sb;
 550 #else
 551         return ERR_PTR(-ENODEV);
 552 #endif
 553 }
 554
 555 /*
 556  * This is the system call interface. This communicates with
 557  * the user-level programs. Currently this only supports diskquota
 558  * calls. Maybe we need to add the process quotas etc. in the future,
 559  * but we probably should use rlimits for that.
 560  */
 561 SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
 562                 qid_t, id, void __user *, addr)
 563 {
 564         uint cmds, type;
 565         struct super_block *sb = NULL;
 566         struct path path, *pathp = NULL;
 567         int ret;
 568
 569         cmds = cmd >> SUBCMDSHIFT;
 570         type = cmd & SUBCMDMASK;
 571
 572         /*
 573          * As a special case Q_SYNC can be called without a specific device.
 574          * It will iterate all superblocks that have quota enabled and call
 575          * the sync action on each of them.
 576          */
 577         if (!special) {
 578                 if (cmds == Q_SYNC)
 579                         return quota_sync_all(type);
 580                 return -ENODEV;
 581         }
 582
 583         /*
 584          * Path for quotaon has to be resolved before grabbing superblock
 585          * because that gets s_umount sem which is also possibly needed by path
 586          * resolution (think about autofs) and thus deadlocks could arise.
 587          */
 588         if (cmds == Q_QUOTAON) {
 589                 ret = user_path_at(AT_FDCWD, addr, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
 590                 if (ret)
 591                         pathp = ERR_PTR(ret);
 592                 else
 593                         pathp = &path;
 594         }
 595
 596         sb = quotactl_block(special, cmds);
 597         if (IS_ERR(sb)) {
 598                 ret = PTR_ERR(sb);
 599                 goto out;
 600         }
 601
 602         ret = do_quotactl(sb, type, cmds, id, addr, pathp);
 603
 604         drop_super(sb);
 605 out:
 606         if (pathp && !IS_ERR(pathp))
 607                 path_put(pathp);
 608         return ret;
 609 }