ash: improve handling of UNC paths

Rework the code in updatepwd() which processes UNC paths so that
the root of a share is properly identified.  This fixes problems
when:

- the current directory is a share and the user changes to '/';

- the current directory is the root of a share and the user tries
  to change to '..'.

1 files changed, 35 insertions, 8 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 10da3ebed..8ed0f19f3 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -2852,6 +2852,34 @@ cdopt(void)
         return flags;
 }
 
+#if ENABLE_PLATFORM_MINGW32
+#define is_path_sep(x) ((x) == '/' || (x) == '\\')
+#define is_unc_path(x) (is_path_sep(x[0]) && is_path_sep(x[1]))
+#define is_root(x) (is_path_sep(x[0]) && x[1] == '\0')
+
+/* 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. */
+static int
+unc_root_len(const char *dir)
+{
+        const char *s = dir + 2;
+        int len;
+
+        if (!is_unc_path(dir))
+                return 0;
+        len = strcspn(s, "/\\");
+        if (len == 0)
+                return 0;
+        s += len + 1;
+        len = strcspn(s, "/\\");
+        if (len == 0)
+                return 0;
+        s += len;
+
+        return s - dir;
+}
+#endif
+
 /*
  * Update curdir (the name of the current directory) in response to a
  * cd command.
@@ -2860,8 +2888,6 @@ static const char *
 updatepwd(const char *dir)
 {
 #if ENABLE_PLATFORM_MINGW32
-#define is_path_sep(x) ((x) == '/' || (x) == '\\')
-#define is_unc_path(x) (is_path_sep(x[0]) && is_path_sep(x[1]))
         /*
          * Due to Windows drive notion, getting pwd is a completely
          * different thing. Handle it in a separate routine
@@ -2871,6 +2897,7 @@ updatepwd(const char *dir)
         char *p;
         char *cdcomppath;
         const char *lim;
+        int len = 0;
         /*
          * There are five cases that make some kind of sense
          *  absdrive +  abspath: c:/path
@@ -2893,15 +2920,18 @@ updatepwd(const char *dir)
         STARTSTACKSTR(new);
         if (!absdrive && curdir == nullstr)
                 return 0;
-        if (!abspath) {
+        if (!abspath || (is_root(dir) && unc_root_len(curdir))) {
                 if (curdir == nullstr)
                         return 0;
                 new = stack_putstr(curdir, new);
         }
         new = makestrspace(strlen(dir) + 2, new);
 
-        if ( is_unc_path(dir) || (!absdrive && !abspath && is_unc_path(curdir)) ) {
-                lim = (char *)stackblock() + 1;
+        if ( (len=unc_root_len(dir)) || ((len=unc_root_len(curdir)) &&
+                                (is_root(dir) || (!absdrive && !abspath))) ) {
+                if (is_root(dir))
+                        new = (char *)stackblock() + len;
+                lim = (char *)stackblock() + len;
         }
         else {
                 char *drive = stackblock();
@@ -2922,15 +2952,12 @@ updatepwd(const char *dir)
         if (!abspath) {
                 if (!is_path_sep(new[-1]))
                         USTPUTC('/', new);
-                if (new > lim && is_path_sep(*lim))
-                        lim++;
         } else {
                 USTPUTC('/', new);
                 cdcomppath ++;
                 if (is_path_sep(dir[1]) && !is_path_sep(dir[2])) {
                         USTPUTC('/', new);
                         cdcomppath++;
-                        lim++;
                 }
         }
         p = strtok(cdcomppath, "/\\");