From 4dcd1e60597c5bd79eab29f49717a13b1b144c8b Mon Sep 17 00:00:00 2001 From: Andrew Kelley Date: Thu, 17 Dec 2020 20:35:29 -0700 Subject: [PATCH] start code: overwrite AT_RANDOM after we use it --- lib/std/start.zig | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/lib/std/start.zig b/lib/std/start.zig index b6fb7e4dfd..6249a6e1ac 100644 --- a/lib/std/start.zig +++ b/lib/std/start.zig @@ -226,11 +226,17 @@ fn posixCallMainAndExit() noreturn { // "The address of sixteen bytes containing a random value." const addr = auxv[i].a_un.a_val; if (addr == 0) break; - const ptr = @intToPtr(*const [16]u8, addr); + const ptr = @intToPtr(*[16]u8, addr); var seed: [32]u8 = undefined; seed[0..16].* = ptr.*; seed[16..].* = ptr.*; tlcsprng.init(seed); + // Overwrite AT_RANDOM after we use it, otherwise our secure + // seed is sitting in memory ready for some other code in the + // program to reuse, and hence break our security. + // We play nice by refreshing it with fresh random bytes + // rather than clearing it. + std.crypto.random.bytes(ptr); break; }, else => continue,