privsep: Avoid the /proc/../ escape

diff --git a/src/privsep-root.c b/src/privsep-root.c
index cba469db9f86fa05545cbc933051e020bdbf330a..5884357af8e6007503ffb0839becfb04a3c35904 100644 (file)
--- a/src/privsep-root.c
+++ b/src/privsep-root.c
@@ -288,6 +288,11 @@ static bool
 ps_root_validpath(const struct dhcpcd_ctx *ctx, uint16_t cmd, const char *path)
 {
 
+       /* Avoid a previous directory attack to avoid /proc/../
+        * dhcpcd should never use a path with double dots. */
+       if (strstr(path, "..") != NULL)
+               return false;
+
        if (cmd == PS_READFILE) {
                if (strcmp(ctx->cffile, path) == 0)
                        return true;