Kernel: Don't leak kmalloc pointers through FIFO absolute paths

Instead of using the FIFO's memory address as part of its absolute path
identity, just use an incrementing FIFO index instead.

Note that this is not used for anything other than debugging (it helps
you identify which file descriptors refer to the same FIFO by looking
at /proc/PID/fds

Kernel/FileSystem/FIFO.cpp

@@ -16,14 +16,7 @@ Lockable<HashTable<FIFO*>>& all_fifos()
     return *s_table;
 }
 
-RefPtr<FIFO> FIFO::from_fifo_id(u32 id)
-{
-    auto* ptr = reinterpret_cast<FIFO*>(id);
-    LOCKER(all_fifos().lock());
-    if (auto it = all_fifos().resource().find(ptr); it == all_fifos().resource().end())
-        return nullptr;
-    return ptr;
-}
+static int s_next_fifo_id = 1;
 
 NonnullRefPtr<FIFO> FIFO::create(uid_t uid)
 {
@@ -43,6 +36,7 @@ FIFO::FIFO(uid_t uid)
 {
     LOCKER(all_fifos().lock());
     all_fifos().resource().set(this);
+    m_fifo_id = ++s_next_fifo_id;
 }
 
 FIFO::~FIFO()
@@ -121,5 +115,5 @@ ssize_t FIFO::write(FileDescription&, const u8* buffer, ssize_t size)
 
 String FIFO::absolute_path(const FileDescription&) const
 {
-    return String::format("fifo:%u", this);
+    return String::format("fifo:%u", m_fifo_id);
 }

Kernel/FileSystem/FIFO.h

@@ -14,8 +14,6 @@ public:
         Writer
     };
 
-    static RefPtr<FIFO> from_fifo_id(u32);
-
     static NonnullRefPtr<FIFO> create(uid_t);
     virtual ~FIFO() override;
 
@@ -43,4 +41,6 @@ private:
     DoubleBuffer m_buffer;
 
     uid_t m_uid { 0 };
+
+    int m_fifo_id { 0 };
 };