[tip: x86/sgx] selftests/sgx: Fix NULL-pointer-dereference upon early test failure

[tip-bot2 for Reinette Chatre]

The following commit has been merged into the x86/sgx branch of tip:

Commit-ID:     2d03861e0d1d1ee81efc59338101cdd86a7474f6
Gitweb:        https://git.kernel.org/tip/2d03861e0d1d1ee81efc59338101cdd86a7474f6
Author:        Reinette Chatre <reinette.chatre@xxxxxxxxx>
AuthorDate:    Tue, 08 Feb 2022 13:48:39 -08:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Fri, 11 Feb 2022 13:52:47 -08:00

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")
Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/90a31dfd640ea756fa324712e7cbab4a90fa7518.1644355600.git.reinette.chatre@xxxxxxxxx
---
 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 9d4322c..006b464 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));
 }