arm64: futex: Avoid copying out uninitialised stack in failed cmpxchg()

Returning an error code from futex_atomic_cmpxchg_inatomic() indicates that the caller should not make any use of *uval, and should instead act upon on the value of the error code. Although this is implemented correctly in our futex code, we needlessly copy uninitialised stack to *uval in the error case, which can easily be avoided. Signed-off-by: Will Deacon <[email protected]>
josf · Apr 26, 2019 · 8e4e0ac · 8e4e0ac
1 parent 03110a5
commit 8e4e0ac
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
@@ -134,7 +134,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *_uaddr,
 	: "memory");
 	uaccess_disable();
 
-	*uval = val;
+	if (!ret)
+		*uval = val;
+
 	return ret;
 }