[Libguestfs] [libguestfs-common PATCH 2/2] options/keys: introduce unescape_device_mapper_lvm()

[Laszlo Ersek]

Introduce unescape_device_mapper_lvm() for turning

  /dev/mapper/VG-LV

key IDs into

  /dev/VG/LV

ones, unescaping doubled hyphens to single hyphens in both VG and LV in
the process. Libguestfs uses the /dev/VG/LV format internally, for
identifying devices, but the user might want to specify the
/dev/mapper/VG-LV ID format with the "--key ID:..." options.

Call unescape_device_mapper_lvm() from key_store_import_key(). That is,
translate the ID as soon as the "--key" option is processed -- let the
keystore only know about the usual /dev/VG/LV format, for later matching.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2168506
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    regcomp() must definitely allocate memory dynamically, and we
    (intentionally) never free that -- we never call regfree(). I assume
    valgrind will catch this as a leak, so we might have to extend
    "valgrind-suppressions" in each dependent superproject. However, I'm
    unable to run "make check-valgrind" successfully in e.g. virt-v2v even
    before these patches; see also
    <https://listman.redhat.com/archives/libguestfs/2023-May/031496.html>.

 options/keys.c | 86 ++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/options/keys.c b/options/keys.c
index bc7459749276..f0164a6ed987 100644
--- a/options/keys.c
+++ b/options/keys.c
@@ -27,6 +27,7 @@
 #include <errno.h>
 #include <error.h>
 #include <assert.h>
+#include <regex.h>
 
 #include "guestfs.h"
 
@@ -260,6 +261,90 @@ key_store_add_from_selector (struct key_store *ks, const char *selector)
   return key_store_import_key (ks, &key);
 }
 
+/* A /dev/mapper/ escaped character is:
+ * - either any character except a slash or a hyphen,
+ * - or a double hyphen.
+ *
+ * Note that parens are deliberately not included here -- they will be included
+ * in the full pattern, for making them more easily countable.
+ *
+ * Also note that the bracket expression below does not contain a range
+ * expression, therefore it should not be locale-sensitive.
+ */
+#define ESC_CH "[^-/]|--"
+
+/* Turn /dev/mapper/VG-LV into /dev/VG/LV. */
+static void
+unescape_device_mapper_lvm (char *id)
+{
+  static bool compiled;
+  int rc;
+  static regex_t regex;
+  regmatch_t match[5];
+  char *output;
+  const char *vg_start, *vg_end, *lv_start, *lv_end;
+  const char *input;
+
+  if (!compiled) {
+    /* Recognize /dev/mapper/VG-LV pathnames, where VG and LV don't contain
+     * slashes, plus any original hyphens in them are doubled for escaping.
+     */
+    static const char pattern[] = "^/dev/("
+                                    "mapper/"
+                                    "((" ESC_CH ")+)"
+                                    "-"
+                                    "((" ESC_CH ")+)"
+                                  ")$";
+
+    rc = regcomp (&regex, pattern, REG_EXTENDED);
+    if (rc != 0) {
+      char errbuf[256];
+
+      /* When regcomp() fails, the contents of "regex" are undefined, so we
+       * cannot pass "regex" to regerror().
+       */
+      (void)regerror (rc, NULL, errbuf, sizeof errbuf);
+      error (EXIT_FAILURE, 0,
+             _("%s: Failed to compile pattern (%s).  Please report a bug for "
+               "libguestfs -- refer to guestfs(3) section BUGS."),
+             __func__, errbuf);
+    }
+    compiled = true;
+  }
+
+  rc = regexec (&regex, id, 5, match, 0);
+
+  /* If there's no match, just leave "id" alone. */
+  if (rc != 0)
+    return;
+
+  /* Start outputting after "/dev/". */
+  output   = id + match[1].rm_so;
+  vg_start = id + match[2].rm_so;
+  vg_end   = id + match[2].rm_eo;
+  lv_start = id + match[4].rm_so;
+  lv_end   = id + match[4].rm_eo;
+
+  /* Each of the following two loops produces at most as many bytes as it
+   * consumes, so we unescape "id" in-place.
+   */
+  input = vg_start;
+  while (input < vg_end)
+    if ((*output++ = *input++) == '-')
+      input++;
+
+  *output++ = '/';
+
+  input = lv_start;
+  while (input < lv_end)
+    if ((*output++ = *input++) == '-')
+      input++;
+
+  *output++ = '\0';
+}
+
+#undef ESC_CH
+
 struct key_store *
 key_store_import_key (struct key_store *ks, struct key_store_key *key)
 {
@@ -278,6 +363,7 @@ key_store_import_key (struct key_store *ks, struct key_store_key *key)
     error (EXIT_FAILURE, errno, "realloc");
 
   ks->keys = new_keys;
+  unescape_device_mapper_lvm (key->id);
   ks->keys[ks->nr_keys] = *key;
   ++ks->nr_keys;