lib/renameatu.c

   1 /* Rename a file relative to open directories.
   2    Copyright (C) 2009-2024 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* written by Eric Blake and Paul Eggert */
  18
  19 #include <config.h>
  20
  21 #include "renameatu.h"
  22
  23 #include <errno.h>
  24 #include <stdio.h>
  25 #include <sys/stat.h>
  26 #include <unistd.h>
  27
  28 #ifdef __linux__
  29 # include <sys/syscall.h>
  30 #endif
  31
  32 static int
  33 errno_fail (int e)
  34 {
  35   errno = e;
  36   return -1;
  37 }
  38
  39 #if HAVE_RENAMEAT
  40
  41 # include <stdlib.h>
  42 # include <string.h>
  43
  44 # include "dirname.h"
  45 # include "openat.h"
  46
  47 #else
  48 # include "openat-priv.h"
  49
  50 static int
  51 rename_noreplace (char const *src, char const *dst)
  52 {
  53   /* This has a race between the call to lstat and the call to rename.  */
  54   struct stat st;
  55   return (lstat (dst, &st) == 0 || errno == EOVERFLOW ? errno_fail (EEXIST)
  56           : errno == ENOENT ? rename (src, dst)
  57           : -1);
  58 }
  59 #endif
  60
  61 #undef renameat
  62
  63 #if HAVE_RENAMEAT
  64
  65 /* Act like renameat (FD1, SRC, FD2, DST), except fail with EEXIST if
  66    FLAGS is nonzero and it is easy to fail atomically if DST already exists.
  67    This lets renameatu be atomic when it can be implemented in terms
  68    of renameatx_np.  */
  69 static int
  70 renameat2ish (int fd1, char const *src, int fd2, char const *dst,
  71               unsigned int flags)
  72 {
  73 # ifdef RENAME_SWAP
  74   if (flags & RENAME_EXCHANGE)
  75     return renameatx_np (fd1, src, fd2, dst, RENAME_SWAP);
  76 # endif
  77 # ifdef RENAME_EXCL
  78   if (flags)
  79     {
  80       int r = renameatx_np (fd1, src, fd2, dst, RENAME_EXCL);
  81       if (r == 0 || (errno != ENOTSUP && errno != ENOSYS))
  82         return r;
  83     }
  84 # endif
  85
  86   return renameat (fd1, src, fd2, dst);
  87 }
  88 #endif
  89
  90 /* Rename FILE1, in the directory open on descriptor FD1, to FILE2, in
  91    the directory open on descriptor FD2.  If possible, do it without
  92    changing the working directory.  Otherwise, resort to using
  93    save_cwd/fchdir, then rename/restore_cwd.  If either the save_cwd or
  94    the restore_cwd fails, then give a diagnostic and exit nonzero.
  95
  96    Obey FLAGS when doing the renaming.  If FLAGS is zero, this
  97    function is equivalent to renameat (FD1, SRC, FD2, DST).
  98    Otherwise, attempt to implement FLAGS even if the implementation is
  99    not atomic; this differs from the GNU/Linux native renameat2,
 100    which fails if it cannot guarantee atomicity.  */
 101
 102 int
 103 renameatu (int fd1, char const *src, int fd2, char const *dst,
 104            unsigned int flags)
 105 {
 106   int ret_val = -1;
 107   int err = EINVAL;
 108
 109 #if HAVE_WORKING_RENAMEAT2
 110   ret_val = renameat2 (fd1, src, fd2, dst, flags);
 111   err = errno;
 112 #elif defined SYS_renameat2
 113   ret_val = syscall (SYS_renameat2, fd1, src, fd2, dst, flags);
 114   err = errno;
 115 #endif
 116
 117   if (! (ret_val < 0 && (err == EINVAL || err == ENOSYS || err == ENOTSUP)))
 118     return ret_val;
 119
 120 #if HAVE_RENAMEAT
 121   {
 122   size_t src_len;
 123   size_t dst_len;
 124   char *src_temp = (char *) src;
 125   char *dst_temp = (char *) dst;
 126   bool src_slash;
 127   bool dst_slash;
 128   int rename_errno = ENOTDIR;
 129   struct stat src_st;
 130   struct stat dst_st;
 131   bool dst_found_nonexistent = false;
 132
 133   switch (flags)
 134     {
 135     case 0:
 136       break;
 137
 138     case RENAME_NOREPLACE:
 139       /* This has a race between the call to fstatat and the calls to
 140          renameat below.  This fstatat is needed even if RENAME_EXCL
 141          is defined, because RENAME_EXCL is buggy on macOS 11.2:
 142          renameatx_np (fd, "X", fd, "X", RENAME_EXCL) incorrectly
 143          succeeds when X exists.  */
 144       if (fstatat (fd2, dst, &dst_st, AT_SYMLINK_NOFOLLOW) == 0
 145           || errno == EOVERFLOW)
 146         return errno_fail (EEXIST);
 147       if (errno != ENOENT)
 148         return -1;
 149       dst_found_nonexistent = true;
 150       break;
 151
 152     case RENAME_EXCHANGE:
 153 #ifdef RENAME_SWAP
 154       break;
 155 #endif
 156     default:
 157       return errno_fail (ENOTSUP);
 158     }
 159
 160   /* Let strace see any ENOENT failure.  */
 161   src_len = strlen (src);
 162   dst_len = strlen (dst);
 163   if (!src_len || !dst_len)
 164     return renameat2ish (fd1, src, fd2, dst, flags);
 165
 166   src_slash = src[src_len - 1] == '/';
 167   dst_slash = dst[dst_len - 1] == '/';
 168   if (!src_slash && !dst_slash)
 169     return renameat2ish (fd1, src, fd2, dst, flags);
 170
 171   /* Presence of a trailing slash requires directory semantics.  If
 172      the source does not exist, or if the destination cannot be turned
 173      into a directory, give up now.  Otherwise, strip trailing slashes
 174      before calling rename.  */
 175   if (fstatat (fd1, src, &src_st, AT_SYMLINK_NOFOLLOW))
 176     return -1;
 177   if (dst_found_nonexistent)
 178     {
 179       if (!S_ISDIR (src_st.st_mode))
 180         return errno_fail (ENOENT);
 181     }
 182   else if (fstatat (fd2, dst, &dst_st, AT_SYMLINK_NOFOLLOW))
 183     {
 184       if (errno != ENOENT || !S_ISDIR (src_st.st_mode))
 185         return -1;
 186     }
 187   else if (!S_ISDIR (dst_st.st_mode))
 188     return errno_fail (ENOTDIR);
 189   else if (!S_ISDIR (src_st.st_mode))
 190     return errno_fail (EISDIR);
 191
 192 # if RENAME_TRAILING_SLASH_SOURCE_BUG
 193   /* See the lengthy comment in rename.c why Solaris 9 is forced to
 194      GNU behavior, while Solaris 10 is left with POSIX behavior,
 195      regarding symlinks with trailing slash.  */
 196   ret_val = -1;
 197   if (src_slash)
 198     {
 199       src_temp = strdup (src);
 200       if (!src_temp)
 201         {
 202           /* Rather than rely on strdup-posix, we set errno ourselves.  */
 203           rename_errno = ENOMEM;
 204           goto out;
 205         }
 206       strip_trailing_slashes (src_temp);
 207       if (fstatat (fd1, src_temp, &src_st, AT_SYMLINK_NOFOLLOW))
 208         {
 209           rename_errno = errno;
 210           goto out;
 211         }
 212       if (S_ISLNK (src_st.st_mode))
 213         goto out;
 214     }
 215   if (dst_slash)
 216     {
 217       dst_temp = strdup (dst);
 218       if (!dst_temp)
 219         {
 220           rename_errno = ENOMEM;
 221           goto out;
 222         }
 223       strip_trailing_slashes (dst_temp);
 224       char readlink_buf[1];
 225       if (readlinkat (fd2, dst_temp, readlink_buf, sizeof readlink_buf) < 0)
 226         {
 227           if (errno != ENOENT && errno != EINVAL)
 228             {
 229               rename_errno = errno;
 230               goto out;
 231             }
 232         }
 233       else
 234         goto out;
 235     }
 236 # endif /* RENAME_TRAILING_SLASH_SOURCE_BUG */
 237
 238   /* renameat does not honor trailing / on Solaris 10.  Solve it in a
 239      similar manner to rename.  No need to worry about bugs not present
 240      on Solaris, since all other systems either lack renameat or honor
 241      trailing slash correctly.  */
 242
 243   ret_val = renameat2ish (fd1, src_temp, fd2, dst_temp, flags);
 244   rename_errno = errno;
 245   goto out;
 246  out:
 247   if (src_temp != src)
 248     free (src_temp);
 249   if (dst_temp != dst)
 250     free (dst_temp);
 251   errno = rename_errno;
 252   return ret_val;
 253   }
 254 #else /* !HAVE_RENAMEAT */
 255
 256   /* RENAME_NOREPLACE is the only flag currently supported.  */
 257   if (flags & ~RENAME_NOREPLACE)
 258     return errno_fail (ENOTSUP);
 259   return at_func2 (fd1, src, fd2, dst, flags ? rename_noreplace : rename);
 260
 261 #endif /* !HAVE_RENAMEAT */
 262 }