dpkg: prevent important directories from being removed

busybox will remove directory symlinks, which is at
odds with common layouts that have some of
bin/lib/lib32/lib64 symlinked.

this adds a exludelist for critcal and often symlinked
directories.

Fixes: Bug 12551

function                                             old     new   delta
remove_file_array                                    139     231     +92

Signed-off-by: Norbert Lange <nolange79@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/archival/dpkg.c b/archival/dpkg.c
index da77fba05..68a40bf6e 100644
--- a/archival/dpkg.c
+++ b/archival/dpkg.c
@@ -1204,6 +1204,27 @@ static char **create_list(const char *filename)
         return file_list;
 }
 
+/** This tests if the filename is an "important" directory, which might be symlinked.
+ *  Debians dpkg test if directories are used by other packages, this
+ *  implementation doesn't and would remove for ex. an lib -> usr/lib symlink.
+ */
+static int is_builtin_exclude(const char *name)
+{
+        if (*name++ != '/')
+                return 0;
+        if (index_in_strings(".\0" "etc\0" "opt\0" "srv\0" "var\0" "var/lib\0",
+                        name) >= 0)
+                return 1;
+        if (is_prefixed_with(name, "usr/")) {
+                name += sizeof("usr/") - 1;
+                if (is_prefixed_with(name, "local/"))
+                        name += sizeof("local/") - 1;
+        }
+
+        return index_in_strings("bin\0" "lib\0" "lib32\0" "lib64\0" "sbin\0",
+                        name) >= 0;
+}
+
 /* maybe i should try and hook this into remove_file.c somehow */
 static int remove_file_array(char **remove_names, char **exclude_names)
 {
@@ -1215,6 +1236,8 @@ static int remove_file_array(char **remove_names, char **exclude_names)
                 return 0;
         }
         for (i = 0; remove_names[i] != NULL; i++) {
+                if (is_builtin_exclude(remove_names[i]))
+                        continue;
                 if (exclude_names != NULL) {
                         for (j = 0; exclude_names[j] != NULL; j++) {
                                 if (strcmp(remove_names[i], exclude_names[j]) == 0) {