libcli: New routine symlink_target_path for [MS-SMB2] 2.2.2.2.1.1

Right now the only user is the user-space symlink following in
smbd. We will use it in libsmb as well to correctly handle
STOPPED_ON_SYMLINK. When trying to upstream that code I found the
previous_slash function incredibly hard to understand.

This new routine makes copy of "const char *_name_in", so that we can
replace previous_slash with a simple strrchr_m. If that's too
slow (which I doubt, this is "only" chasing symlinks) we can always do
something smarter again.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

diff --git a/libcli/smb/reparse.c b/libcli/smb/reparse.c
index 08071ca85d76dbba3f2469dafda225064535e549..ffadf1c35af9d42a0af50929580b14f9aaf702fa 100644 (file)
--- a/libcli/smb/reparse.c
+++ b/libcli/smb/reparse.c
@@ -565,3 +565,97 @@ ssize_t reparse_data_buffer_marshall(const struct reparse_data_buffer *src,
 
        return ret;
 }
+
+/*
+ * Implement [MS-SMB2] 2.2.2.2.1.1 Handling the Symbolic Link Error Response
+ */
+
+int symlink_target_path(TALLOC_CTX *ctx,
+                       const char *_name_in,
+                       size_t num_unparsed,
+                       const char *substitute,
+                       bool relative,
+                       char separator,
+                       char **_target)
+{
+       size_t name_in_len = strlen(_name_in);
+       size_t num_parsed;
+       char name_in[name_in_len + 1];
+       char *unparsed = NULL;
+       char *syml = NULL;
+       char *target = NULL;
+
+       if (num_unparsed > name_in_len) {
+               return EINVAL;
+       }
+       num_parsed = name_in_len - num_unparsed;
+
+       /*
+        * We need to NULL out separators in name_in. Make a copy of
+        * _name_in, which is a const char *.
+        */
+       memcpy(name_in, _name_in, sizeof(name_in));
+
+       unparsed = name_in + num_parsed;
+
+       if ((num_unparsed != 0) && (unparsed[0] != separator)) {
+               /*
+                * Symlinks in the middle of name_in must end in a separator
+                */
+               return EINVAL;
+       }
+
+       if (!relative) {
+               /*
+                * From [MS-SMB2] 2.2.2.2.1.1:
+                *
+                * If the SYMLINK_FLAG_RELATIVE flag is not set in the Flags
+                * field of the symbolic link error response, the unparsed
+                * portion of the file name MUST be appended to the substitute
+                * name to create the new target path name.
+                */
+               target = talloc_asprintf(ctx, "%s%s", substitute, unparsed);
+               goto done;
+       }
+
+       /*
+        * From [MS-SMB2] 2.2.2.2.1.1:
+        *
+        * If the SYMLINK_FLAG_RELATIVE flag is set in the Flags field
+        * of the symbolic link error response, the symbolic link name
+        * MUST be identified by backing up one path name element from
+        * the unparsed portion of the path name. The symbolic link
+        * MUST be replaced with the substitute name to create the new
+        * target path name.
+        */
+
+       {
+               char symlink_end_char = unparsed[0]; /* '\0' or a separator */
+
+               unparsed[0] = '\0';
+               syml = strrchr_m(name_in, separator);
+               unparsed[0] = symlink_end_char;
+       }
+
+       if (syml == NULL) {
+               /*
+                * Nothing to back up to, the symlink was the first
+                * path component.
+                */
+               name_in[0] = '\0';
+       } else {
+               /*
+                * Make "name_in" up to the symlink usable for asprintf
+                */
+               syml[1] = '\0';
+       }
+
+       target = talloc_asprintf(ctx, "%s%s%s", name_in, substitute, unparsed);
+
+done:
+       if (target == NULL) {
+               return ENOMEM;
+       }
+       *_target = target;
+       return 0;
+}

diff --git a/libcli/smb/reparse.h b/libcli/smb/reparse.h
index e4410d974e4f148918f08e3a9e19e3611cd86b94..78c55ca324550d5f1897104fd10705a01dd88313 100644 (file)
--- a/libcli/smb/reparse.h
+++ b/libcli/smb/reparse.h
@@ -79,4 +79,12 @@ ssize_t reparse_data_buffer_marshall(const struct reparse_data_buffer *src,
                                     uint8_t *buf,
                                     size_t buflen);
 
+int symlink_target_path(TALLOC_CTX *ctx,
+                       const char *_name_in,
+                       size_t num_unparsed,
+                       const char *substitute,
+                       bool relative,
+                       char separator,
+                       char **_target);
+
 #endif