src/basic/xattr-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <stdint.h>
   6 #include <stdlib.h>
   7 #include <string.h>
   8 #include <sys/time.h>
   9 #include <sys/xattr.h>
  10
  11 #include "alloc-util.h"
  12 #include "fd-util.h"
  13 #include "macro.h"
  14 #include "missing.h"
  15 #include "sparse-endian.h"
  16 #include "stdio-util.h"
  17 #include "string-util.h"
  18 #include "time-util.h"
  19 #include "xattr-util.h"
  20
  21 int getxattr_malloc(const char *path, const char *name, char **value, bool allow_symlink) {
  22         char *v;
  23         size_t l;
  24         ssize_t n;
  25
  26         assert(path);
  27         assert(name);
  28         assert(value);
  29
  30         for (l = 100; ; l = (size_t) n + 1) {
  31                 v = new0(char, l);
  32                 if (!v)
  33                         return -ENOMEM;
  34
  35                 if (allow_symlink)
  36                         n = lgetxattr(path, name, v, l);
  37                 else
  38                         n = getxattr(path, name, v, l);
  39
  40                 if (n >= 0 && (size_t) n < l) {
  41                         *value = v;
  42                         return n;
  43                 }
  44
  45                 free(v);
  46
  47                 if (n < 0 && errno != ERANGE)
  48                         return -errno;
  49
  50                 if (allow_symlink)
  51                         n = lgetxattr(path, name, NULL, 0);
  52                 else
  53                         n = getxattr(path, name, NULL, 0);
  54                 if (n < 0)
  55                         return -errno;
  56         }
  57 }
  58
  59 int fgetxattr_malloc(int fd, const char *name, char **value) {
  60         char *v;
  61         size_t l;
  62         ssize_t n;
  63
  64         assert(fd >= 0);
  65         assert(name);
  66         assert(value);
  67
  68         for (l = 100; ; l = (size_t) n + 1) {
  69                 v = new0(char, l);
  70                 if (!v)
  71                         return -ENOMEM;
  72
  73                 n = fgetxattr(fd, name, v, l);
  74
  75                 if (n >= 0 && (size_t) n < l) {
  76                         *value = v;
  77                         return n;
  78                 }
  79
  80                 free(v);
  81
  82                 if (n < 0 && errno != ERANGE)
  83                         return -errno;
  84
  85                 n = fgetxattr(fd, name, NULL, 0);
  86                 if (n < 0)
  87                         return -errno;
  88         }
  89 }
  90
  91 int fgetxattrat_fake(
  92                 int dirfd,
  93                 const char *filename,
  94                 const char *attribute,
  95                 void *value, size_t size,
  96                 int flags,
  97                 size_t *ret_size) {
  98
  99         char fn[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
 100         _cleanup_close_ int fd = -1;
 101         ssize_t l;
 102
 103         /* The kernel doesn't have a fgetxattrat() command, hence let's emulate one */
 104
 105         if (flags & ~(AT_SYMLINK_NOFOLLOW|AT_EMPTY_PATH))
 106                 return -EINVAL;
 107
 108         if (isempty(filename)) {
 109                 if (!(flags & AT_EMPTY_PATH))
 110                         return -EINVAL;
 111
 112                 xsprintf(fn, "/proc/self/fd/%i", dirfd);
 113         } else {
 114                 fd = openat(dirfd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
 115                 if (fd < 0)
 116                         return -errno;
 117
 118                 xsprintf(fn, "/proc/self/fd/%i", fd);
 119         }
 120
 121         l = getxattr(fn, attribute, value, size);
 122         if (l < 0)
 123                 return -errno;
 124
 125         *ret_size = l;
 126         return 0;
 127 }
 128
 129 static int parse_crtime(le64_t le, usec_t *usec) {
 130         uint64_t u;
 131
 132         assert(usec);
 133
 134         u = le64toh(le);
 135         if (IN_SET(u, 0, (uint64_t) -1))
 136                 return -EIO;
 137
 138         *usec = (usec_t) u;
 139         return 0;
 140 }
 141
 142 int fd_getcrtime_at(int dirfd, const char *name, usec_t *ret, int flags) {
 143         struct_statx sx
 144 #if HAS_FEATURE_MEMORY_SANITIZER
 145                 = {}
 146 #  warning "Explicitly initializing struct statx, to work around msan limitation. Please remove as soon as msan has been updated to not require this."
 147 #endif
 148                 ;
 149         usec_t a, b;
 150         le64_t le;
 151         size_t n;
 152         int r;
 153
 154         assert(ret);
 155
 156         if (flags & ~(AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW))
 157                 return -EINVAL;
 158
 159         /* So here's the deal: the creation/birth time (crtime/btime) of a file is a relatively newly supported concept
 160          * on Linux (or more strictly speaking: a concept that only recently got supported in the API, it was
 161          * implemented on various file systems on the lower level since a while, but never was accessible). However, we
 162          * needed a concept like that for vaccuuming algorithms and such, hence we emulated it via a user xattr for a
 163          * long time. Starting with Linux 4.11 there's statx() which exposes the timestamp to userspace for the first
 164          * time, where it is available. Thius function will read it, but it tries to keep some compatibility with older
 165          * systems: we try to read both the crtime/btime and the xattr, and then use whatever is older. After all the
 166          * concept is useful for determining how "old" a file really is, and hence using the older of the two makes
 167          * most sense. */
 168
 169         if (statx(dirfd, strempty(name), flags|AT_STATX_DONT_SYNC, STATX_BTIME, &sx) >= 0 &&
 170             (sx.stx_mask & STATX_BTIME) &&
 171             sx.stx_btime.tv_sec != 0)
 172                 a = (usec_t) sx.stx_btime.tv_sec * USEC_PER_SEC +
 173                         (usec_t) sx.stx_btime.tv_nsec / NSEC_PER_USEC;
 174         else
 175                 a = USEC_INFINITY;
 176
 177         r = fgetxattrat_fake(dirfd, name, "user.crtime_usec", &le, sizeof(le), flags, &n);
 178         if (r >= 0) {
 179                 if (n != sizeof(le))
 180                         r = -EIO;
 181                 else
 182                         r = parse_crtime(le, &b);
 183         }
 184         if (r < 0) {
 185                 if (a != USEC_INFINITY) {
 186                         *ret = a;
 187                         return 0;
 188                 }
 189
 190                 return r;
 191         }
 192
 193         if (a != USEC_INFINITY)
 194                 *ret = MIN(a, b);
 195         else
 196                 *ret = b;
 197
 198         return 0;
 199 }
 200
 201 int fd_getcrtime(int fd, usec_t *ret) {
 202         return fd_getcrtime_at(fd, NULL, ret, AT_EMPTY_PATH);
 203 }
 204
 205 int path_getcrtime(const char *p, usec_t *ret) {
 206         return fd_getcrtime_at(AT_FDCWD, p, ret, 0);
 207 }
 208
 209 int fd_setcrtime(int fd, usec_t usec) {
 210         le64_t le;
 211
 212         assert(fd >= 0);
 213
 214         if (IN_SET(usec, 0, USEC_INFINITY))
 215                 usec = now(CLOCK_REALTIME);
 216
 217         le = htole64((uint64_t) usec);
 218         if (fsetxattr(fd, "user.crtime_usec", &le, sizeof(le), 0) < 0)
 219                 return -errno;
 220
 221         return 0;
 222 }