[msan] Check qsort input.

Summary:
Qsort interceptor suppresses all checks by unpoisoning the data in the
wrapper of a comparator function, and then unpoisoning the output array
as well.

This change adds an explicit run of the comparator on all elements of
the input array to catch any sanitizer bugs.

Reviewers: vitalybuka

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D71780

2 files changed, 19 insertions, 0 deletions

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc b/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
index 8f365ee3085..47e344c9e3f 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -9670,6 +9670,13 @@ INTERCEPTOR(void, qsort, void *base, SIZE_T nmemb, SIZE_T size,
             qsort_compar_f compar) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, qsort, base, nmemb, size, compar);
+  // Run the comparator over all array elements to detect any memory issues.
+  for (SIZE_T i = 0; i < nmemb - 1; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    void *q = (void *)((char *)base + (i + 1) * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(2);
+    compar(p, q);
+  }
   qsort_compar_f old_compar = qsort_compar;
   qsort_compar = compar;
   SIZE_T old_size = qsort_size;
@@ -9699,6 +9706,13 @@ INTERCEPTOR(void, qsort_r, void *base, SIZE_T nmemb, SIZE_T size,
             qsort_r_compar_f compar, void *arg) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, qsort_r, base, nmemb, size, compar, arg);
+  // Run the comparator over all array elements to detect any memory issues.
+  for (SIZE_T i = 0; i < nmemb - 1; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    void *q = (void *)((char *)base + (i + 1) * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(3);
+    compar(p, q, arg);
+  }
   qsort_r_compar_f old_compar = qsort_r_compar;
   qsort_r_compar = compar;
   SIZE_T old_size = qsort_r_size;
diff --git a/compiler-rt/test/msan/qsort.cpp b/compiler-rt/test/msan/qsort.cpp
index eb869701186..cf754012b22 100644
--- a/compiler-rt/test/msan/qsort.cpp
+++ b/compiler-rt/test/msan/qsort.cpp
@@ -1,4 +1,5 @@
 // RUN: %clangxx_msan -O0 -g %s -o %t && %run %t
+// RUN: %clangxx_msan -DPOISON -O0 -g %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 #include <assert.h>
 #include <errno.h>
@@ -65,6 +66,10 @@ int main(int argc, char *argv[]) {
   for (int i = 0; i < kSize1; ++i)
     p[i] = i * 2 + (i % 3 - 1) * 3;
   poison_stack_and_param();
+#ifdef POISON
+  __msan_poison(p + 1, sizeof(long));
+  // CHECK: Uninitialized bytes in __msan_check_mem_is_initialized at offset 0 inside [{{.*}}, 8)
+#endif
   qsort(p, kSize1, sizeof(long), compar1);
   __msan_check_mem_is_initialized(p, sizeof(long) * kSize1);
   assert(seen2);