slab: detect corrupted slab and invalid frees

and report about that.

Fixes #2350

repos/base/run/slab.run

@@ -1,3 +1,8 @@
+if {[get_cmd_switch --autopilot] && [have_include "power_on/qemu"]} {
+	puts "\nRunning slab benchmark in autopilot on Qemu is not recommended.\n"
+	exit
+}
+
 build "core init drivers/timer test/slab"
 
 create_boot_directory

repos/base/src/lib/base/slab.cc

@@ -23,6 +23,8 @@ using namespace Genode;
  */
 class Genode::Slab::Block
 {
+	friend struct Genode::Slab::Entry;
+
 	public:
 
 		Block *next = this;  /* next block in ring     */
@@ -71,6 +73,12 @@ class Genode::Slab::Block
 		 */
 		int _slab_entry_idx(Entry *e);
 
+		/**
+		 * These functions are called by Slab::Entry.
+		 */
+		void inc_avail(Entry &e);
+		void dec_avail() { _avail--; }
+
 	public:
 
 		/**
@@ -96,12 +104,6 @@ class Genode::Slab::Block
 		 * Return a used slab block entry
 		 */
 		Entry *any_used_entry();
-
-		/**
-		 * These functions are called by Slab::Entry.
-		 */
-		void inc_avail(Entry &e);
-		void dec_avail() { _avail--; }
 };
 
 
@@ -124,6 +126,9 @@ struct Genode::Slab::Entry
 			block.inc_avail(*this);
 		}
 
+		bool used() {
+			return block._state(block._slab_entry_idx(this)) == Block::USED; }
+
 		/**
 		 * Lookup Entry by given address
 		 *
@@ -317,7 +322,7 @@ bool Slab::alloc(size_t size, void **out_addr)
 
 	/* too large for us ? */
 	if (size > _slab_size) {
-		Genode::error("requested size ", size, " is larger then slab size ",
+		error("requested size ", size, " is larger then slab size ",
 		      _slab_size);
 		return false;
 	}
@@ -370,8 +375,20 @@ void Slab::_free(void *addr)
 	if (!e)
 		return;
 
+	if (addr < (void *)((addr_t)&e->block + sizeof(e->block)) ||
+	    addr >= (void *)((addr_t)&e->block + _block_size)) {
+		error("slab block ", Hex_range<addr_t>((addr_t)&e->block, _block_size),
+		      " is corrupt - slab address ", addr);
+		return;
+	}
+
 	Block &block = e->block;
 
+	if (!e->used()) {
+		error("slab address ", addr, " freed which is unused");
+		return;
+	}
+
 	e->~Entry();
 	_total_avail++;
 

repos/base/src/test/slab/main.cc

@@ -2,7 +2,6 @@
  * \brief  Slab allocator test
  * \author Norman Feske
  * \date   2015-03-31
- *
  */
 
 /*
@@ -65,7 +64,7 @@ struct Array_of_slab_elements
 
 void Component::construct(Genode::Env & env)
 {
-	Genode::Heap heap(env.ram(), env.rm());
+	static Genode::Heap heap(env.ram(), env.rm());
 
 	log("--- slab test ---");
 
@@ -94,7 +93,7 @@ void Component::construct(Genode::Env & env)
 		 * take the overhead of the two block allocations at the heap into
 		 * account.
 		 */
-		enum { HEAP_OVERHEAD = 36 };
+		enum { HEAP_OVERHEAD = 9*sizeof(long) };
 		if (alloc.consumed() > 2*(BLOCK_SIZE + HEAP_OVERHEAD)) {
 			error("slab failed to release empty slab blocks");
 			return;
@@ -108,5 +107,21 @@ void Component::construct(Genode::Env & env)
 		return;
 	}
 
+	{
+		log("test double-free detection - error message is expected");
+
+		Genode::Slab slab(SLAB_SIZE, BLOCK_SIZE, nullptr, &alloc);
+
+		void *p = nullptr;
+		{
+			Array_of_slab_elements array(slab, 4096, SLAB_SIZE, heap);
+			p = array.elem[1705];
+		}
+		slab.free(p, SLAB_SIZE);
+		{
+			Array_of_slab_elements array(slab, 4096, SLAB_SIZE, heap);
+		}
+	}
+
 	log("Test done");
 }

tool/autopilot.list

@@ -90,3 +90,4 @@ trace
 input_filter
 init
 nic_dump
+slab