Rewrite /proc/self/mountinfo handling to cope with bind-mounts and
move-mounts appearing out of order. Fixes Ubuntu bug #738345. * grub-core/kern/emu/getroot.c (find_root_device_from_mountinfo): Build a list of relevant visible mounts using the mnt_id and parent_mnt_id fields, and then scan that list at the end.
This commit is contained in:
Colin Watson
parent
9d5f81622c
commit
78fa584f67
2 changed files with 90 additions and 19 deletions
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@ -1,3 +1,12 @@
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2011-04-13 Colin Watson <cjwatson@ubuntu.com>
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Rewrite /proc/self/mountinfo handling to cope with bind-mounts and
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move-mounts appearing out of order. Fixes Ubuntu bug #738345.
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* grub-core/kern/emu/getroot.c (find_root_device_from_mountinfo):
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Build a list of relevant visible mounts using the mnt_id and
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parent_mnt_id fields, and then scan that list at the end.
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2011-04-12 Colin Watson <cjwatson@ubuntu.com>
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* docs/grub.texi (normal): New section.
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@ -98,6 +98,14 @@ xgetcwd (void)
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#ifdef __linux__
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struct mountinfo_entry
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{
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int id;
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int major, minor;
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char enc_root[PATH_MAX], enc_path[PATH_MAX];
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char fstype[PATH_MAX], device[PATH_MAX];
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};
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/* Statting something on a btrfs filesystem always returns a virtual device
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major/minor pair rather than the real underlying device, because btrfs
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can span multiple underlying devices (and even if it's currently only
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@ -112,6 +120,10 @@ grub_find_root_device_from_mountinfo (const char *dir, char **relroot)
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char *buf = NULL;
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size_t len = 0;
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char *ret = NULL;
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int entry_len = 0, entry_max = 4;
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struct mountinfo_entry *entries;
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struct mountinfo_entry parent_entry = { 0, 0, 0, "", "", "", "" };
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int i;
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if (! *dir)
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dir = "/";
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@ -122,52 +134,102 @@ grub_find_root_device_from_mountinfo (const char *dir, char **relroot)
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if (! fp)
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return NULL; /* fall through to other methods */
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entries = xmalloc (entry_max * sizeof (*entries));
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/* First, build a list of relevant visible mounts. */
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while (getline (&buf, &len, fp) > 0)
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{
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int mnt_id, parent_mnt_id;
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unsigned int major, minor;
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char enc_root[PATH_MAX], enc_path[PATH_MAX];
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struct mountinfo_entry entry;
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int count;
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size_t enc_path_len;
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const char *sep;
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char fstype[PATH_MAX], device[PATH_MAX];
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if (sscanf (buf, "%d %d %u:%u %s %s%n",
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&mnt_id, &parent_mnt_id, &major, &minor, enc_root, enc_path,
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&count) < 6)
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&entry.id, &parent_entry.id, &entry.major, &entry.minor,
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entry.enc_root, entry.enc_path, &count) < 6)
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continue;
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enc_path_len = strlen (enc_path);
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enc_path_len = strlen (entry.enc_path);
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/* Check that enc_path is a prefix of dir. The prefix must either be
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the entire string, or end with a slash, or be immediately followed
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by a slash. */
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if (strncmp (dir, enc_path, enc_path_len) != 0 ||
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if (strncmp (dir, entry.enc_path, enc_path_len) != 0 ||
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(enc_path_len && dir[enc_path_len - 1] != '/' &&
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dir[enc_path_len] && dir[enc_path_len] != '/'))
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continue;
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/* This is a parent of the requested directory. /proc/self/mountinfo
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is in mount order, so it must be the closest parent we've
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encountered so far. If it's virtual, return its device node;
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otherwise, carry on to try to find something closer. */
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free (ret);
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ret = NULL;
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sep = strstr (buf + count, " - ");
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if (!sep)
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continue;
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sep += sizeof (" - ") - 1;
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if (sscanf (sep, "%s %s", fstype, device) != 2)
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if (sscanf (sep, "%s %s", entry.fstype, entry.device) != 2)
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continue;
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ret = strdup (device);
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/* Using the mount IDs, find out where this fits in the list of
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visible mount entries we've seen so far. There are three
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interesting cases. Firstly, it may be inserted at the end: this is
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the usual case of /foo/bar being mounted after /foo. Secondly, it
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may be inserted at the start: for example, this can happen for
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filesystems that are mounted before / and later moved under it.
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Thirdly, it may occlude part or all of the existing filesystem
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tree, in which case the end of the list needs to be pruned and this
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new entry will be inserted at the end. */
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if (entry_len >= entry_max)
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{
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entry_max <<= 1;
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entries = xrealloc (entries, entry_max * sizeof (*entries));
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}
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if (!entry_len)
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{
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/* Initialise list. */
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entry_len = 2;
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entries[0] = parent_entry;
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entries[1] = entry;
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}
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else
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{
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for (i = entry_len - 1; i >= 0; i--)
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{
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if (entries[i].id == parent_entry.id)
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{
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/* Insert at end, pruning anything previously above this. */
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entry_len = i + 2;
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entries[i + 1] = entry;
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break;
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}
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else if (i == 0 && entries[i].id == entry.id)
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{
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/* Insert at start. */
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entry_len++;
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memmove (entries + 1, entries,
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(entry_len - 1) * sizeof (*entries));
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entries[0] = parent_entry;
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entries[1] = entry;
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break;
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}
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}
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}
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}
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/* Now scan visible mounts for the ones we're interested in. */
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for (i = entry_len - 1; i >= 0; i--)
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{
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if (entries[i].major != 0)
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continue; /* not a virtual device */
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if (!*entries[i].device)
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continue;
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ret = strdup (entries[i].device);
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if (relroot)
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*relroot = strdup (enc_root);
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*relroot = strdup (entries[i].enc_root);
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break;
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}
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free (buf);
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free (entries);
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fclose (fp);
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return ret;
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}
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