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authorMichal Hocko <mhocko@suse.com>2017-08-18 15:16:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-18 15:32:01 -0700
commit6b31d5955cb29a51c5baffee382f213d75e98fb8 (patch)
tree86405062da720e3cc0f60c9c0e48e21e3ab0189c /mm/huge_memory.c
parent5b53a6ea886700a128b697a6fe8375340dea2c30 (diff)
mm, oom: fix potential data corruption when oom_reaper races with writer
Wenwei Tao has noticed that our current assumption that the oom victim is dying and never doing any visible changes after it dies, and so the oom_reaper can tear it down, is not entirely true. __task_will_free_mem consider a task dying when SIGNAL_GROUP_EXIT is set but do_group_exit sends SIGKILL to all threads _after_ the flag is set. So there is a race window when some threads won't have fatal_signal_pending while the oom_reaper could start unmapping the address space. Moreover some paths might not check for fatal signals before each PF/g-u-p/copy_from_user. We already have a protection for oom_reaper vs. PF races by checking MMF_UNSTABLE. This has been, however, checked only for kernel threads (use_mm users) which can outlive the oom victim. A simple fix would be to extend the current check in handle_mm_fault for all tasks but that wouldn't be sufficient because the current check assumes that a kernel thread would bail out after EFAULT from get_user*/copy_from_user and never re-read the same address which would succeed because the PF path has established page tables already. This seems to be the case for the only existing use_mm user currently (virtio driver) but it is rather fragile in general. This is even more fragile in general for more complex paths such as generic_perform_write which can re-read the same address more times (e.g. iov_iter_copy_from_user_atomic to fail and then iov_iter_fault_in_readable on retry). Therefore we have to implement MMF_UNSTABLE protection in a robust way and never make a potentially corrupted content visible. That requires to hook deeper into the PF path and check for the flag _every time_ before a pte for anonymous memory is established (that means all !VM_SHARED mappings). The corruption can be triggered artificially (http://lkml.kernel.org/r/201708040646.v746kkhC024636@www262.sakura.ne.jp) but there doesn't seem to be any real life bug report. The race window should be quite tight to trigger most of the time. Link: http://lkml.kernel.org/r/20170807113839.16695-3-mhocko@kernel.org Fixes: aac453635549 ("mm, oom: introduce oom reaper") Signed-off-by: Michal Hocko <mhocko@suse.com> Reported-by: Wenwei Tao <wenwei.tww@alibaba-inc.com> Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Andrea Argangeli <andrea@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/huge_memory.c')
-rw-r--r--mm/huge_memory.c30
1 files changed, 22 insertions, 8 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 216114f6ef0b..90731e3b7e58 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -32,6 +32,7 @@
#include <linux/userfaultfd_k.h>
#include <linux/page_idle.h>
#include <linux/shmem_fs.h>
+#include <linux/oom.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>
@@ -550,6 +551,7 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
struct mem_cgroup *memcg;
pgtable_t pgtable;
unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+ int ret = 0;
VM_BUG_ON_PAGE(!PageCompound(page), page);
@@ -561,9 +563,8 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
pgtable = pte_alloc_one(vma->vm_mm, haddr);
if (unlikely(!pgtable)) {
- mem_cgroup_cancel_charge(page, memcg, true);
- put_page(page);
- return VM_FAULT_OOM;
+ ret = VM_FAULT_OOM;
+ goto release;
}
clear_huge_page(page, haddr, HPAGE_PMD_NR);
@@ -576,13 +577,14 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
if (unlikely(!pmd_none(*vmf->pmd))) {
- spin_unlock(vmf->ptl);
- mem_cgroup_cancel_charge(page, memcg, true);
- put_page(page);
- pte_free(vma->vm_mm, pgtable);
+ goto unlock_release;
} else {
pmd_t entry;
+ ret = check_stable_address_space(vma->vm_mm);
+ if (ret)
+ goto unlock_release;
+
/* Deliver the page fault to userland */
if (userfaultfd_missing(vma)) {
int ret;
@@ -610,6 +612,15 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
}
return 0;
+unlock_release:
+ spin_unlock(vmf->ptl);
+release:
+ if (pgtable)
+ pte_free(vma->vm_mm, pgtable);
+ mem_cgroup_cancel_charge(page, memcg, true);
+ put_page(page);
+ return ret;
+
}
/*
@@ -688,7 +699,10 @@ int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
ret = 0;
set = false;
if (pmd_none(*vmf->pmd)) {
- if (userfaultfd_missing(vma)) {
+ ret = check_stable_address_space(vma->vm_mm);
+ if (ret) {
+ spin_unlock(vmf->ptl);
+ } else if (userfaultfd_missing(vma)) {
spin_unlock(vmf->ptl);
ret = handle_userfault(vmf, VM_UFFD_MISSING);
VM_BUG_ON(ret & VM_FAULT_FALLBACK);