[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

1 files changed, 18 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 2d9636a9c87..68a9db5bba7 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -9665,6 +9665,15 @@ 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; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(2);
+    // Compare each element with itself to trigger an equality check, which
+    // typically requires the comparator to look as many of the object fields as
+    // possible.
+    compar(p, p);
+  }
   qsort_compar_f old_compar = qsort_compar;
   qsort_compar = compar;
   SIZE_T old_size = qsort_size;
@@ -9694,6 +9703,15 @@ 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; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(3);
+    // Compare each element with itself to trigger an equality check, which
+    // typically requires the comparator to look as many of the object fields as
+    // possible.
+    compar(p, p, arg);
+  }
   qsort_r_compar_f old_compar = qsort_r_compar;
   qsort_r_compar = compar;
   SIZE_T old_size = qsort_r_size;