Handle zero-length mmaps correctly

newbiecodingman · Jun 16, 2020 · 0754471 · 0754471
1 parent 95dc3f5
commit 0754471
Show file tree

Hide file tree

Showing 3 changed files with 3 additions and 4 deletions.
diff --git a/emu/memory.h b/emu/memory.h
@@ -45,7 +45,8 @@ void mem_next_page(struct mem *mem, page_t *page);
 #define PAGE(addr) ((addr) >> PAGE_BITS)
 #define PGOFFSET(addr) ((addr) & (PAGE_SIZE - 1))
 typedef dword_t pages_t;
-#define PAGE_ROUND_UP(bytes) (((bytes - 1) / PAGE_SIZE) + 1)
+// bytes MUST be unsigned if you would like this to overflow to zero
+#define PAGE_ROUND_UP(bytes) (PAGE((bytes) + PAGE_SIZE - 1))
 
 #define BYTES_ROUND_DOWN(bytes) (PAGE(bytes) << PAGE_BITS)
 #define BYTES_ROUND_UP(bytes) (PAGE_ROUND_UP(bytes) << PAGE_BITS)

diff --git a/fs/real.c b/fs/real.c
@@ -263,9 +263,6 @@ int realfs_poll(struct fd *fd) {
 }
 
 int realfs_mmap(struct fd *fd, struct mem *mem, page_t start, pages_t pages, off_t offset, int prot, int flags) {
-    if (pages == 0)
-        return 0;
-
     int mmap_flags = 0;
     if (flags & MMAP_PRIVATE) mmap_flags |= MAP_PRIVATE;
     if (flags & MMAP_SHARED) mmap_flags |= MAP_SHARED;

diff --git a/kernel/mmap.c b/kernel/mmap.c
@@ -50,6 +50,7 @@ void mm_release(struct mm *mm) {
 static addr_t do_mmap(addr_t addr, dword_t len, dword_t prot, dword_t flags, fd_t fd_no, dword_t offset) {
     int err;
     pages_t pages = PAGE_ROUND_UP(len);
+    if (!pages) return _EINVAL;
     page_t page;
     if (addr != 0) {
         if (PGOFFSET(addr) != 0)