linux-stable.git/mm, branch v3.2.92

mm: fix find_vma_prev

2017-07-02T16:12:48+00:00

commit 83cd904d271ba960c53f3adbb037f3486518f1e6 upstream.

Commit 6bd4837de96e ("mm: simplify find_vma_prev()") broke memory
management on PA-RISC.

After application of the patch, programs that allocate big arrays on the
stack crash with segfault, for example, this will crash if compiled
without optimization:

  int main()
  {
	char array[200000];
	array[199999] = 0;
	return 0;
  }

The reason is that PA-RISC has up-growing stack and the stack is usually
the last memory area.  In the above example, a page fault happens above
the stack.

Previously, if we passed too high address to find_vma_prev, it returned
NULL and stored the last VMA in *pprev.  After "simplify find_vma_prev"
change, it stores NULL in *pprev.  Consequently, the stack area is not
found and it is not expanded, as it used to be before the change.

This patch restores the old behavior and makes it return the last VMA in
*pprev if the requested address is higher than address of any other VMA.

Signed-off-by: Mikulas Patocka 
Acked-by: KOSAKI Motohiro 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

mm: simplify find_vma_prev()

2017-07-02T16:12:48+00:00

commit 6bd4837de96e7d9f9bf33e59117c24fc230862ac upstream.

commit 297c5eee37 ("mm: make the vma list be doubly linked") added the
vm_prev member to vm_area_struct.  We can simplify find_vma_prev() by
using it.  Also, this change helps to improve page fault performance
because it has stronger locality of reference.

Signed-off-by: KOSAKI Motohiro 
Reviewed-by: KAMEZAWA Hiroyuki 
Cc: Hugh Dickins 
Cc: Peter Zijlstra 
Cc: Shaohua Li 
Cc: Michal Hocko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

Allow stack to grow up to address space limit

2017-07-02T16:12:47+00:00

commit bd726c90b6b8ce87602208701b208a208e6d5600 upstream.

Fix expand_upwards() on architectures with an upward-growing stack (parisc,
metag and partly IA-64) to allow the stack to reliably grow exactly up to
the address space limit given by TASK_SIZE.

Signed-off-by: Helge Deller 
Acked-by: Hugh Dickins 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

mm: larger stack guard gap, between vmas

2017-07-02T16:12:47+00:00

commit 1be7107fbe18eed3e319a6c3e83c78254b693acb upstream.

Stack guard page is a useful feature to reduce a risk of stack smashing
into a different mapping. We have been using a single page gap which
is sufficient to prevent having stack adjacent to a different mapping.
But this seems to be insufficient in the light of the stack usage in
userspace. E.g. glibc uses as large as 64kB alloca() in many commonly
used functions. Others use constructs liks gid_t buffer[NGROUPS_MAX]
which is 256kB or stack strings with MAX_ARG_STRLEN.

This will become especially dangerous for suid binaries and the default
no limit for the stack size limit because those applications can be
tricked to consume a large portion of the stack and a single glibc call
could jump over the guard page. These attacks are not theoretical,
unfortunatelly.

Make those attacks less probable by increasing the stack guard gap
to 1MB (on systems with 4k pages; but make it depend on the page size
because systems with larger base pages might cap stack allocations in
the PAGE_SIZE units) which should cover larger alloca() and VLA stack
allocations. It is obviously not a full fix because the problem is
somehow inherent, but it should reduce attack space a lot.

One could argue that the gap size should be configurable from userspace,
but that can be done later when somebody finds that the new 1MB is wrong
for some special case applications.  For now, add a kernel command line
option (stack_guard_gap) to specify the stack gap size (in page units).

Implementation wise, first delete all the old code for stack guard page:
because although we could get away with accounting one extra page in a
stack vma, accounting a larger gap can break userspace - case in point,
a program run with "ulimit -S -v 20000" failed when the 1MB gap was
counted for RLIMIT_AS; similar problems could come with RLIMIT_MLOCK
and strict non-overcommit mode.

Instead of keeping gap inside the stack vma, maintain the stack guard
gap as a gap between vmas: using vm_start_gap() in place of vm_start
(or vm_end_gap() in place of vm_end if VM_GROWSUP) in just those few
places which need to respect the gap - mainly arch_get_unmapped_area(),
and and the vma tree's subtree_gap support for that.

Original-patch-by: Oleg Nesterov 
Original-patch-by: Michal Hocko 
Signed-off-by: Hugh Dickins 
Acked-by: Michal Hocko 
Tested-by: Helge Deller  # parisc
Signed-off-by: Linus Torvalds 
[Hugh Dickins: Backported to 3.2]
[bwh: Fix more instances of vma->vm_start in sparc64 impl. of
 arch_get_unmapped_area_topdown() and generic impl. of
 hugetlb_get_unmapped_area()]
Signed-off-by: Ben Hutchings

mm: do not grow the stack vma just because of an overrun on preceding vma

2017-07-02T16:12:47+00:00

commit 09884964335e85e897876d17783c2ad33cf8a2e0 upstream.

The stack vma is designed to grow automatically (marked with VM_GROWSUP
or VM_GROWSDOWN depending on architecture) when an access is made beyond
the existing boundary.  However, particularly if you have not limited
your stack at all ("ulimit -s unlimited"), this can cause the stack to
grow even if the access was really just one past *another* segment.

And that's wrong, especially since we first grow the segment, but then
immediately later enforce the stack guard page on the last page of the
segment.  So _despite_ first growing the stack segment as a result of
the access, the kernel will then make the access cause a SIGSEGV anyway!

So do the same logic as the guard page check does, and consider an
access to within one page of the next segment to be a bad access, rather
than growing the stack to abut the next segment.

Reported-and-tested-by: Heiko Carstens 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

mm/mempolicy.c: fix error handling in set_mempolicy and mbind.

2017-06-05T20:13:54+00:00

commit cf01fb9985e8deb25ccf0ea54d916b8871ae0e62 upstream.

In the case that compat_get_bitmap fails we do not want to copy the
bitmap to the user as it will contain uninitialized stack data and leak
sensitive data.

Signed-off-by: Chris Salls 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

mm/huge_memory.c: fix up "mm/huge_memory.c: respect FOLL_FORCE/FOLL_COW for thp" backport

2017-04-04T21:18:32+00:00

This is a stable follow up fix for an incorrect backport. The issue is
not present in the upstream kernel.

Miroslav has noticed the following splat when testing my 3.2 forward
port of 8310d48b125d ("mm/huge_memory.c: respect FOLL_FORCE/FOLL_COW for
thp") to 3.12:

BUG: Bad page state in process a.out  pfn:26400
page:ffffea000085e000 count:0 mapcount:1 mapping:          (null) index:0x7f049d600
page flags: 0x1fffff80108018(uptodate|dirty|head|swapbacked)
page dumped because: nonzero mapcount
[iii]
CPU: 2 PID: 5926 Comm: a.out Tainted: G            E    3.12.61-0-default #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
 0000000000000000 ffffffff81515830 ffffea000085e000 ffffffff81800ad7
 ffffffff815118a5 ffffea000085e000 0000000000000000 000fffff80000000
 ffffffff81140f18 fff000007c000000 ffffea000085e000 0000000000000009
Call Trace:
 [] dump_trace+0x7d/0x2d0
 [] show_stack_log_lvl+0x94/0x170
 [] show_stack+0x21/0x50
 [] dump_stack+0x5d/0x78
 [] bad_page.part.67+0xe8/0x102
 [] free_pages_prepare+0x198/0x1b0
 [] __free_pages_ok+0x15/0xd0
 [] __access_remote_vm+0x7c/0x1e0
 [] mem_rw.isra.13+0x14b/0x1a0
 [] vfs_write+0xb8/0x1e0
 [] SyS_pwrite64+0x6b/0xa0
 [] system_call_fastpath+0x16/0x1b
 [<00007f049da18573>] 0x7f049da18572

The problem is that the original 3.2 backport didn't return NULL page on
the FOLL_COW page and so the page got reused.

Reported-and-tested-by: Miroslav Beneš 
Signed-off-by: Michal Hocko 
Signed-off-by: Ben Hutchings

mm, fs: check for fatal signals in do_generic_file_read()

2017-03-16T02:18:47+00:00

commit 5abf186a30a89d5b9c18a6bf93a2c192c9fd52f6 upstream.

do_generic_file_read() can be told to perform a large request from
userspace.  If the system is under OOM and the reading task is the OOM
victim then it has an access to memory reserves and finishing the full
request can lead to the full memory depletion which is dangerous.  Make
sure we rather go with a short read and allow the killed task to
terminate.

Link: http://lkml.kernel.org/r/20170201092706.9966-3-mhocko@kernel.org
Signed-off-by: Michal Hocko 
Reviewed-by: Christoph Hellwig 
Cc: Tetsuo Handa 
Cc: Al Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

mm/huge_memory.c: respect FOLL_FORCE/FOLL_COW for thp

2017-03-16T02:18:46+00:00

commit 8310d48b125d19fcd9521d83b8293e63eb1646aa upstream.

In commit 19be0eaffa3a ("mm: remove gup_flags FOLL_WRITE games from
__get_user_pages()"), the mm code was changed from unsetting FOLL_WRITE
after a COW was resolved to setting the (newly introduced) FOLL_COW
instead.  Simultaneously, the check in gup.c was updated to still allow
writes with FOLL_FORCE set if FOLL_COW had also been set.

However, a similar check in huge_memory.c was forgotten.  As a result,
remote memory writes to ro regions of memory backed by transparent huge
pages cause an infinite loop in the kernel (handle_mm_fault sets
FOLL_COW and returns 0 causing a retry, but follow_trans_huge_pmd bails
out immidiately because `(flags & FOLL_WRITE) && !pmd_write(*pmd)` is
true.

While in this state the process is stil SIGKILLable, but little else
works (e.g.  no ptrace attach, no other signals).  This is easily
reproduced with the following code (assuming thp are set to always):

    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 

    #define TEST_SIZE 5 * 1024 * 1024

    int main(void) {
      int status;
      pid_t child;
      int fd = open("/proc/self/mem", O_RDWR);
      void *addr = mmap(NULL, TEST_SIZE, PROT_READ,
                        MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
      assert(addr != MAP_FAILED);
      pid_t parent_pid = getpid();
      if ((child = fork()) == 0) {
        void *addr2 = mmap(NULL, TEST_SIZE, PROT_READ | PROT_WRITE,
                           MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
        assert(addr2 != MAP_FAILED);
        memset(addr2, 'a', TEST_SIZE);
        pwrite(fd, addr2, TEST_SIZE, (uintptr_t)addr);
        return 0;
      }
      assert(child == waitpid(child, &status, 0));
      assert(WIFEXITED(status) && WEXITSTATUS(status) == 0);
      return 0;
    }

Fix this by updating follow_trans_huge_pmd in huge_memory.c analogously
to the update in gup.c in the original commit.  The same pattern exists
in follow_devmap_pmd.  However, we should not be able to reach that
check with FOLL_COW set, so add WARN_ONCE to make sure we notice if we
ever do.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170106015025.GA38411@juliacomputing.com
Signed-off-by: Keno Fischer 
Acked-by: Kirill A. Shutemov 
Cc: Greg Thelen 
Cc: Nicholas Piggin 
Cc: Willy Tarreau 
Cc: Oleg Nesterov 
Cc: Kees Cook 
Cc: Andy Lutomirski 
Cc: Michal Hocko 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.2:
 - Drop change to follow_devmap_pmd()
 - pmd_dirty() is not available; check the page flags as in
   can_follow_write_pte()
 - Adjust context]
Signed-off-by: Ben Hutchings

swapfile: fix memory corruption via malformed swapfile

2017-02-23T03:50:59+00:00

commit dd111be69114cc867f8e826284559bfbc1c40e37 upstream.

When root activates a swap partition whose header has the wrong
endianness, nr_badpages elements of badpages are swabbed before
nr_badpages has been checked, leading to a buffer overrun of up to 8GB.

This normally is not a security issue because it can only be exploited
by root (more specifically, a process with CAP_SYS_ADMIN or the ability
to modify a swap file/partition), and such a process can already e.g.
modify swapped-out memory of any other userspace process on the system.

Link: http://lkml.kernel.org/r/1477949533-2509-1-git-send-email-jann@thejh.net
Signed-off-by: Jann Horn 
Acked-by: Kees Cook 
Acked-by: Jerome Marchand 
Acked-by: Johannes Weiner 
Cc: "Kirill A. Shutemov" 
Cc: Vlastimil Babka 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings