2 files changed, 18 insertions, 3 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 9fa212b014a5..f1867900e459 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1929,7 +1929,10 @@ static int elf_core_dump(long signr, struct pt_regs *regs, struct file *file, un
         elf = kmalloc(sizeof(*elf), GFP_KERNEL);
         if (!elf)
                 goto out;
-        
+        /*
+         * The number of segs are recored into ELF header as 16bit value.
+         * Please check DEFAULT_MAX_MAP_COUNT definition when you modify here.
+         */
         segs = current->mm->map_count;
 #ifdef ELF_CORE_EXTRA_PHDRS
         segs += ELF_CORE_EXTRA_PHDRS;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d0754269884..0085d758d645 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -349,8 +349,20 @@ extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner);
 struct nsproxy;
 struct user_namespace;
 
-/* Maximum number of active map areas.. This is a random (large) number */
-#define DEFAULT_MAX_MAP_COUNT   65536
+/*
+ * Default maximum number of active map areas, this limits the number of vmas
+ * per mm struct. Users can overwrite this number by sysctl but there is a
+ * problem.
+ *
+ * When a program's coredump is generated as ELF format, a section is created
+ * per a vma. In ELF, the number of sections is represented in unsigned short.
+ * This means the number of sections should be smaller than 65535 at coredump.
+ * Because the kernel adds some informative sections to a image of program at
+ * generating coredump, we need some margin. The number of extra sections is
+ * 1-3 now and depends on arch. We use "5" as safe margin, here.
+ */
+#define MAPCOUNT_ELF_CORE_MARGIN        (5)
+#define DEFAULT_MAX_MAP_COUNT   (USHORT_MAX - MAPCOUNT_ELF_CORE_MARGIN)
 
 extern int sysctl_max_map_count;