Do not initialize the allocator on free(nullptr).

[eugenis]

Bionic calls free(nullptr) before the allocator settings are finalized. Scudo should not run allocator initialization at that time. Doing so causes various bad things to happen, like mapping primary regions with the wrong PROT_MTE setting.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Evgenii Stepanov (eugenis)

Changes

Bionic calls free(nullptr) before the allocator settings are finalized. Scudo should not run allocator initialization at that time. Doing so causes various bad things to happen, like mapping primary regions with the wrong PROT_MTE setting.

---

Full diff: https://github.com/llvm/llvm-project/pull/74366.diff

1 Files Affected:

• (modified) compiler-rt/lib/scudo/standalone/combined.h (+3-3)

diff --git a/compiler-rt/lib/scudo/standalone/combined.h b/compiler-rt/lib/scudo/standalone/combined.h
index 25c597199a658..79c3a36c742b4 100644
--- a/compiler-rt/lib/scudo/standalone/combined.h
+++ b/compiler-rt/lib/scudo/standalone/combined.h
@@ -522,6 +522,9 @@ class Allocator {
 
   NOINLINE void deallocate(void *Ptr, Chunk::Origin Origin, uptr DeleteSize = 0,
                            UNUSED uptr Alignment = MinAlignment) {
+    if (UNLIKELY(!Ptr))
+      return;
+
     // For a deallocation, we only ensure minimal initialization, meaning thread
     // local data will be left uninitialized for now (when using ELF TLS). The
     // fallback cache will be used instead. This is a workaround for a situation
@@ -530,9 +533,6 @@ class Allocator {
     // being destroyed properly. Any other heap operation will do a full init.
     initThreadMaybe(/*MinimalInit=*/true);
 
-    if (UNLIKELY(!Ptr))
-      return;
-
 #ifdef GWP_ASAN_HOOKS
     if (UNLIKELY(GuardedAlloc.pointerIsMine(Ptr))) {
       GuardedAlloc.deallocate(Ptr);

[cferris1000]

LGTM.

[ChiaHungDuan]

LGTM. BTW, I think this change still makes sense even without the case mentioned in the description. I may revise the description a little bit to say some logic change and then mention the potential problem in bionic.

[eugenis]

Thanks! I tweaked the description as you suggested.