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Author: Raphael Geissert <geissert@debian.org>
Bug-Debian: https://bugs.debian.org/731860
Description: Avoid directory traversal when extracting archives
 by skipping over leading slashes and any prefix containing ".." components.
Forwarded: yes

--- a/lib/decode.c
+++ b/lib/decode.c
@@ -22,6 +22,36 @@
 #endif
 
 
+char *
+safer_name_suffix (char const *file_name)
+{
+       char const *p, *t;
+       p = t = file_name;
+       while (*p == '/') t = ++p;
+       while (*p)
+       {
+               while (p[0] == '.' && p[0] == p[1] && p[2] == '/')
+               {
+                       p += 3;
+                       t = p;
+               }
+               /* advance pointer past the next slash */
+               while (*p && (p++)[0] != '/');
+       }
+
+       if (!*t)
+       {
+               t = ".";
+       }
+
+       if (t != file_name)
+       {
+               /* TODO: warn somehow that the path was modified */
+       }
+       return (char*)t;
+}
+
+
 /* determine full path name */
 char *
 th_get_pathname(TAR *t)
@@ -29,17 +59,17 @@ th_get_pathname(TAR *t)
        static char filename[MAXPATHLEN];
 
        if (t->th_buf.gnu_longname)
-               return t->th_buf.gnu_longname;
+               return safer_name_suffix(t->th_buf.gnu_longname);
 
        if (t->th_buf.prefix[0] != '\0')
        {
                snprintf(filename, sizeof(filename), "%.155s/%.100s",
                         t->th_buf.prefix, t->th_buf.name);
-               return filename;
+               return safer_name_suffix(filename);
        }
 
        snprintf(filename, sizeof(filename), "%.100s", t->th_buf.name);
-       return filename;
+       return safer_name_suffix(filename);
 }
 
 
--- a/lib/extract.c
+++ b/lib/extract.c
@@ -298,14 +298,14 @@ tar_extract_hardlink(TAR * t, char *real
        if (mkdirhier(dirname(filename)) == -1)
                return -1;
        libtar_hashptr_reset(&hp);
-       if (libtar_hash_getkey(t->h, &hp, th_get_linkname(t),
+       if (libtar_hash_getkey(t->h, &hp, safer_name_suffix(th_get_linkname(t)),
                               (libtar_matchfunc_t)libtar_str_match) != 0)
        {
                lnp = (char *)libtar_hashptr_data(&hp);
                linktgt = &lnp[strlen(lnp) + 1];
        }
        else
-               linktgt = th_get_linkname(t);
+               linktgt = safer_name_suffix(th_get_linkname(t));
 
 #ifdef DEBUG
        printf("  ==> extracting: %s (link to %s)\n", filename, linktgt);
@@ -343,9 +343,9 @@ tar_extract_symlink(TAR *t, char *realna
 
 #ifdef DEBUG
        printf("  ==> extracting: %s (symlink to %s)\n",
-              filename, th_get_linkname(t));
+              filename, safer_name_suffix(th_get_linkname(t)));
 #endif
-       if (symlink(th_get_linkname(t), filename) == -1)
+       if (symlink(safer_name_suffix(th_get_linkname(t)), filename) == -1)
        {
 #ifdef DEBUG
                perror("symlink()");
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -15,3 +15,4 @@
 
 #include <libtar.h>
 
+char* safer_name_suffix(char const*);