[musl] [RESEND PATCH] ldso/dynlink: Protect LD_ env vars from getting clobbered by apps

[Elvis Pranskevichus <elvis@edgedb.com>]

(sorry, the previous patch is obviously wrong, this is a better
version)

There is no guarantee that the environment block will remain intact.
For example, PostgreSQL clobbers argv/environ area to implement its
"setproctitle" emulation on non-BSD [1], and there is a popular Python
library inspired by it [2].  As a result, setting `LD_LIBRARY_PATH`
or `LD_PRELOAD` has no effect on Postgres subprocesses when linking
against musl.

Protect against this by making a copies instead of storing the original
pointers directly.
---
 ldso/dynlink.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index cc677952..2b816ce0 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1757,7 +1757,23 @@ void __dls3(size_t *sp, size_t *auxv)
 	/* Only trust user/env if kernel says we're not suid/sgid */
 	if (!libc.secure) {
 		env_path = getenv("LD_LIBRARY_PATH");
+		if (env_path != NULL) {
+			/* Prevent value from getting clobbered by the application */
+			env_path = strdup(env_path);
+			if (!env_path) {
+				dprintf(2, "%s: out of memory\n", argv[0]);
+				_exit(127);
+			}
+		}
 		env_preload = getenv("LD_PRELOAD");
+		if (env_preload != NULL) {
+			/* Prevent value from getting clobbered by the application */
+			env_preload = strdup(env_preload);
+			if (!env_preload) {
+				dprintf(2, "%s: out of memory\n", argv[0]);
+				_exit(127);
+			}
+		}
 	}
 
 	/* Activate error handler function */
-- 
2.35.1