linux-stable/fs/proc
Andrea Arcangeli 04f5866e41 coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping
The core dumping code has always run without holding the mmap_sem for
writing, despite that is the only way to ensure that the entire vma
layout will not change from under it.  Only using some signal
serialization on the processes belonging to the mm is not nearly enough.
This was pointed out earlier.  For example in Hugh's post from Jul 2017:

  https://lkml.kernel.org/r/alpine.LSU.2.11.1707191716030.2055@eggly.anvils

  "Not strictly relevant here, but a related note: I was very surprised
   to discover, only quite recently, how handle_mm_fault() may be called
   without down_read(mmap_sem) - when core dumping. That seems a
   misguided optimization to me, which would also be nice to correct"

In particular because the growsdown and growsup can move the
vm_start/vm_end the various loops the core dump does around the vma will
not be consistent if page faults can happen concurrently.

Pretty much all users calling mmget_not_zero()/get_task_mm() and then
taking the mmap_sem had the potential to introduce unexpected side
effects in the core dumping code.

Adding mmap_sem for writing around the ->core_dump invocation is a
viable long term fix, but it requires removing all copy user and page
faults and to replace them with get_dump_page() for all binary formats
which is not suitable as a short term fix.

For the time being this solution manually covers the places that can
confuse the core dump either by altering the vma layout or the vma flags
while it runs.  Once ->core_dump runs under mmap_sem for writing the
function mmget_still_valid() can be dropped.

Allowing mmap_sem protected sections to run in parallel with the
coredump provides some minor parallelism advantage to the swapoff code
(which seems to be safe enough by never mangling any vma field and can
keep doing swapins in parallel to the core dumping) and to some other
corner case.

In order to facilitate the backporting I added "Fixes: 86039bd3b4e6"
however the side effect of this same race condition in /proc/pid/mem
should be reproducible since before 2.6.12-rc2 so I couldn't add any
other "Fixes:" because there's no hash beyond the git genesis commit.

Because find_extend_vma() is the only location outside of the process
context that could modify the "mm" structures under mmap_sem for
reading, by adding the mmget_still_valid() check to it, all other cases
that take the mmap_sem for reading don't need the new check after
mmget_not_zero()/get_task_mm().  The expand_stack() in page fault
context also doesn't need the new check, because all tasks under core
dumping are frozen.

Link: http://lkml.kernel.org/r/20190325224949.11068-1-aarcange@redhat.com
Fixes: 86039bd3b4 ("userfaultfd: add new syscall to provide memory externalization")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Jann Horn <jannh@google.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jann Horn <jannh@google.com>
Acked-by: Jason Gunthorpe <jgg@mellanox.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-04-19 09:46:05 -07:00
..
array.c proc: use seq_puts() everywhere 2019-03-05 21:07:22 -08:00
base.c ptrace: Remove maxargs from task_current_syscall() 2019-04-04 09:17:15 -04:00
cmdline.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
consoles.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
cpuinfo.c x86 / CPU: Always show current CPU frequency in /proc/cpuinfo 2017-11-15 19:46:50 +01:00
devices.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
fd.c proc: use "unsigned int" in proc_fill_cache() 2018-06-07 17:34:38 -07:00
fd.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
generic.c proc: fix /proc/net/* after setns(2) 2019-02-01 15:46:22 -08:00
inode.c proc: Add fs_context support to procfs 2019-02-28 03:29:28 -05:00
internal.h Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 14:08:19 -07:00
interrupts.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
Kconfig proc/kcore: add vmcoreinfo note to /proc/kcore 2018-08-22 10:52:46 -07:00
kcore.c fs/proc/kcore.c: make kcore_modules static 2019-03-29 10:01:37 -07:00
kmsg.c vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
loadavg.c sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD 2018-10-26 16:26:32 -07:00
Makefile proc: : uninline name_to_int() 2017-11-17 16:10:00 -08:00
meminfo.c mm, proc: add KReclaimable to /proc/meminfo 2018-10-26 16:26:32 -07:00
namespaces.c procfs: switch instantiate_t to d_splice_alias() 2018-05-26 14:20:50 -04:00
nommu.c proc: introduce proc_create_seq{,_data} 2018-05-16 07:23:35 +02:00
page.c mm: convert PG_balloon to PG_offline 2019-03-05 21:07:14 -08:00
proc_net.c proc: fix /proc/net/* after setns(2) 2019-02-01 15:46:22 -08:00
proc_sysctl.c fs/proc/proc_sysctl.c: fix NULL pointer dereference in put_links 2019-03-29 10:01:38 -07:00
proc_tty.c tty: replace ->proc_fops with ->proc_show 2018-05-16 07:24:30 +02:00
root.c Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 14:08:19 -07:00
self.c fs/proc/self.c: code cleanup for proc_setup_self() 2019-03-05 21:07:21 -08:00
softirqs.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
stat.c Merge branch 'akpm' (patches from Andrew) 2019-03-06 10:31:36 -08:00
task_mmu.c coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping 2019-04-19 09:46:05 -07:00
task_nommu.c Merge branch 'akpm' (patches from Andrew) 2019-03-06 10:31:36 -08:00
thread_self.c fs/proc/thread_self.c: code cleanup for proc_setup_thread_self() 2019-03-05 21:07:21 -08:00
uptime.c fs/proc/uptime.c: use ktime_get_boottime_ts64 2018-08-22 10:52:45 -07:00
util.c fs/proc/util.c: include fs/proc/internal.h for name_to_int() 2019-01-04 13:13:45 -08:00
version.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
vmcore.c mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00