Avoid dangling ptrs in header and data params for PEM_read_bio_ex

In the event of a failure in PEM_read_bio_ex() we free the buffers we
allocated for the header and data buffers. However we were not clearing
the ptrs stored in *header and *data. Since, on success, the caller is
responsible for freeing these ptrs this can potentially lead to a double
free if the caller frees them even on failure.

Thanks to Dawei Wang for reporting this issue.

Based on a proposed patch by Kurt Roeckx.

CVE-2022-4450

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>

diff --git a/crypto/pem/pem_lib.c b/crypto/pem/pem_lib.c
index 4035ac64e67e0b9a1ffa3eabbf84981029365583..f7a1bd830217edd79f8559399c56a829d4347fd7 100644 (file)
--- a/crypto/pem/pem_lib.c
+++ b/crypto/pem/pem_lib.c
@@ -995,7 +995,9 @@ int PEM_read_bio_ex(BIO *bp, char **name_out, char **header,
 
 out_free:
     PEM_FREE(*header, flags, 0);
+    *header = NULL;
     PEM_FREE(*data, flags, 0);
+    *data = NULL;
 end:
     EVP_ENCODE_CTX_free(ctx);
     PEM_FREE(name, flags, 0);