[merged] elf-limit-max-map-count-to-safe-value.patch removed from -mm tree

[merged] elf-limit-max-map-count-to-safe-value.patch removed from -mm tree

[akpm]

The patch titled
     elf: limit max map count to safe value
has been removed from the -mm tree.  Its filename was
     elf-limit-max-map-count-to-safe-value.patch

This patch was dropped because it was merged into mainline or a subsystem tree

The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/

------------------------------------------------------
Subject: elf: limit max map count to safe value
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

With ELF, at generating coredump, some more headers other than used
vmas are added.

When max_map_count == 65536, a core generated by following kinds of
code can be unreadable because the number of ELF's program header is
written in 16bit in Ehdr (please see elf.h) and the number overflows.

==
	... = mmap(); (munmap, mprotect, etc...)
	if (failed)
		abort();
==

This can happen in mmap/munmap/mprotect/etc...which calls split_vma().

I think 65536 is not safe as _default_ and reduce it to 65530 is good
for avoiding unexpected corrupted core.

Anyway, max_map_count can be enlarged by sysctl if a user is brave..

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Jakub Jelinek <jakub@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/binfmt_elf.c       |    5 ++++-
 include/linux/sched.h |   16 ++++++++++++++--
 2 files changed, 18 insertions(+), 3 deletions(-)

diff -puN fs/binfmt_elf.c~elf-limit-max-map-count-to-safe-value fs/binfmt_elf.c
--- a/fs/binfmt_elf.c~elf-limit-max-map-count-to-safe-value
+++ a/fs/binfmt_elf.c
@@ -1929,7 +1929,10 @@ static int elf_core_dump(long signr, str
 	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 -puN include/linux/sched.h~elf-limit-max-map-count-to-safe-value include/linux/sched.h
--- a/include/linux/sched.h~elf-limit-max-map-count-to-safe-value
+++ a/include/linux/sched.h
@@ -349,8 +349,20 @@ extern int mutex_spin_on_owner(struct mu
 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;
 
_

Patches currently in -mm which might be from kamezawa.hiroyu@jp.fujitsu.com are

origin.patch
vmscan-dont-attempt-to-reclaim-anon-page-in-lumpy-reclaim-when-no-swap-space-is-available.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup-fix.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup-fix-2.patch
memcg-add-comments-explaining-memory-barriers.patch
memcg-add-comments-explaining-memory-barriers-checkpatch-fixes.patch