ash: improve handling of UNC paths

Be more strict about identifying UNC paths in unc_root_len().

In updatepwd() in ash:

- Skip duplicate leading slashes unless the directory is a UNC path.
- Rewrite detection and handling of the five possible types of path.

This improves cases like 'cd ///' and 'cd /xyz' when the current
directory is a UNC path.

See GitHub issue #192.

2 files changed, 56 insertions, 38 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 3c53b25ff..397995d9a 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -2998,7 +2998,8 @@ updatepwd(const char *dir)
         char *p;
         char *cdcomppath;
         const char *lim;
-        int len = 0;
+        int len;
+        char buffer[PATH_MAX];
         /*
          * There are five cases that make some kind of sense
          *
@@ -3006,65 +3007,81 @@ updatepwd(const char *dir)
          *    c:/path
          *    //host/share
          *
-         * Relative to current drive:
+         * Relative to current working directory of other drive:
+         *    c:path
+         *
+         * Relative to current root (drive/share):
          *    /path
          *
-         * Relative to current working directory of current drive
+         * Relative to current working directory of current root (drive/share):
          *    path
-         *
-         * Relative to current working directory of other drive
-         *    c:path
          */
-        int absdrive = has_dos_drive_prefix(dir);
-        int curr_relpath = !absdrive && !is_path_sep(*dir);
-        int other_relpath = absdrive && !is_path_sep(dir[2]);
-        int relpath = curr_relpath || other_relpath;
+        enum {ABS_DRIVE, ABS_SHARE, REL_OTHER, REL_ROOT, REL_CWD} target;
+
+        /* skip multiple leading separators unless dir is a UNC path */
+        if (is_path_sep(*dir) && unc_root_len(dir) == 0) {
+                while (is_path_sep(dir[1]))
+                        ++dir;
+        }
+
+        len = strlen(dir);
+        if (len >= 2 && has_dos_drive_prefix(dir))
+                target = len >= 3 && is_path_sep(dir[2]) ? ABS_DRIVE : REL_OTHER;
+        else if (unc_root_len(dir) != 0)
+                target = ABS_SHARE;
+        else if (is_path_sep(*dir))
+                target = REL_ROOT;
+        else
+                target = REL_CWD;
 
         cdcomppath = sstrdup(dir);
         STARTSTACKSTR(new);
 
-        /* prefix new path with current directory, if required */
-        if (other_relpath) {
+        switch (target) {
+        case REL_OTHER:
                 /* c:path */
-                char buffer[PATH_MAX];
-
                 if (get_drive_cwd(dir, buffer, PATH_MAX) == NULL)
                         return 0;
                 new = stack_putstr(buffer, new);
-        }
-        else if (curr_relpath || (is_root(dir) && unc_root_len(curdir))) {
-                /* relative path on current drive or explicit root of UNC curdir */
-                if (curdir == nullstr)
+                len = 2;
+                cdcomppath += len;
+                dir += len;
+                break;
+        case REL_CWD:
+        case REL_ROOT:
+                /* path or /path */
+                len = root_len(curdir);
+                if (len == 0)
                         return 0;
-                new = stack_putstr(curdir, new);
+                new = target == REL_CWD ? stack_putstr(curdir, new) :
+                                                                        stnputs(curdir, len, new);
+                break;
+        default:
+                /* //host/share or c:/path */
+                len = root_len(dir);
+                if (len == 0)
+                        return 0;
+                new = stnputs(dir, len, new);
+                cdcomppath += len;
+                dir += len;
+                break;
         }
 
         new = makestrspace(strlen(dir) + 2, new);
+        lim = (char *)stackblock() + len + 1;
 
-        if ( (len=unc_root_len(dir)) || ((len=unc_root_len(curdir)) &&
-                                (is_root(dir) || curr_relpath)) ) {
-                /* //host/share or path relative to //host/share */
-                lim = (char *)stackblock() + len;
-        }
-        else {
-                if (absdrive) {
-                        if (!relpath)
-                                new = stnputs(dir, 2, new);
-                        cdcomppath += 2;
-                        dir += 2;
-                }
-                lim = (char *)stackblock() + 3;
-        }
-
-        if (relpath) {
+        if (!is_path_sep(*dir)) {
                 if (!is_path_sep(new[-1]))
                         USTPUTC('/', new);
+                if (new > lim && is_path_sep(*lim))
+                        lim++;
         } else {
                 USTPUTC('/', new);
-                cdcomppath ++;
+                cdcomppath++;
                 if (is_path_sep(dir[1]) && !is_path_sep(dir[2])) {
                         USTPUTC('/', new);
                         cdcomppath++;
+                        lim++;
                 }
         }
         p = strtok(cdcomppath, "/\\");
@@ -3086,7 +3103,7 @@ updatepwd(const char *dir)
                         new = stack_putstr(p, new);
                         USTPUTC('/', new);
                 }
-                p = strtok(0, "/\\");
+                p = strtok(NULL, "/\\");
         }
         if (new > lim)
                 STUNPUTC(new);
diff --git a/win32/mingw.c b/win32/mingw.c
index 06b22a2ed..78d662e50 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1643,7 +1643,8 @@ void hide_console(void)
 #endif
 
 #define is_path_sep(x) ((x) == '/' || (x) == '\\')
-#define is_unc_path(x) (is_path_sep(x[0]) && is_path_sep(x[1]))
+#define is_unc_path(x) (strlen(x) > 4 && is_path_sep(x[0]) && \
+                                                        is_path_sep(x[1]) && !is_path_sep(x[2]))
 
 /* Return the length of the root of a UNC path, i.e. the '//host/share'
  * component, or 0 if the path doesn't look like that. */