The patch titled
elf: limit max map count to safe value
has been added to the -mm tree. Its filename is
elf-limit-max-map-count-to-safe-value.patch
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------------------------------------------------------
Subject: elf: limit max map count to safe value
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Cc: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Acked-by: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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
@@ -351,8 +351,20 @@ 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@xxxxxxxxxxxxxx are
origin.patch
elf-limit-max-map-count-to-safe-value.patch
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