linux-kernel - [PATCH V3 1/4] selftests/sgx: Fix NULL-pointer-dereference upon early test failure

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Message-Id: <90a31dfd640ea756fa324712e7cbab4a90fa7518.1644355600.git.reinette.chatre@intel.com>
Date:   Tue,  8 Feb 2022 13:48:39 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     dave.hansen@...ux.intel.com, jarkko@...nel.org, tglx@...utronix.de,
        bp@...en8.de, luto@...nel.org, mingo@...hat.com,
        linux-sgx@...r.kernel.org, x86@...nel.org, shuah@...nel.org
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH V3 1/4] selftests/sgx: Fix NULL-pointer-dereference upon early test failure

== Background ==

The SGX selftests track parts of the enclave binaries in an array:
encl->segment_tbl[]. That array is dynamically allocated early
(but not first) in the test's lifetime. The array is referenced
at the end of the test in encl_delete().

== Problem ==

encl->segment_tbl[] can be NULL if the test fails before its
allocation. That leads to a NULL-pointer-dereference in encl_delete().
This is triggered during early failures of the selftest like if the
enclave binary ("test_encl.elf") is deleted.

== Solution ==

Ensure encl->segment_tbl[] is valid before attempting to access
its members. The offset with which it is accessed, encl->nr_segments,
is initialized before encl->segment_tbl[] and thus considered valid
to use after the encl->segment_tbl[] check succeeds.

Fixes: 3200505d4de6 ("selftests/sgx: Create a heap for the test enclave")
Acked-by: Shuah Khan <skhan@...uxfoundation.org>
Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
---
Changes since V2:
- Add Acked by from Shuah.

Changes since V1:
- Rewrite commit message (Dave).

 tools/testing/selftests/sgx/load.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/sgx/load.c b/tools/testing/selftests/sgx/load.c
index 9d4322c946e2..006b464c8fc9 100644
--- a/tools/testing/selftests/sgx/load.c
+++ b/tools/testing/selftests/sgx/load.c
@@ -21,7 +21,7 @@
 
 void encl_delete(struct encl *encl)
 {
-	struct encl_segment *heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
+	struct encl_segment *heap_seg;
 
 	if (encl->encl_base)
 		munmap((void *)encl->encl_base, encl->encl_size);
@@ -32,10 +32,11 @@ void encl_delete(struct encl *encl)
 	if (encl->fd)
 		close(encl->fd);
 
-	munmap(heap_seg->src, heap_seg->size);
-
-	if (encl->segment_tbl)
+	if (encl->segment_tbl) {
+		heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
+		munmap(heap_seg->src, heap_seg->size);
 		free(encl->segment_tbl);
+	}
 
 	memset(encl, 0, sizeof(*encl));
 }
-- 
2.25.1