Messages in this thread Patch in this message |  | | Subject | [PATCH v2 2/2] kernel/fork: set VMA's mm/prev/next right after vm_area_dup in dup_mmap | From | Konstantin Khlebnikov <> | Date | Tue, 07 Jan 2020 13:19:58 +0300 |
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Function vm_area_dup() makes exact copy of structure. It's better to stop referencing parent structures because various helpers use these pointers.
For example if VM_WIPEONFORK is set then anon_vma_prepare() will try to merge anon_vma with previous and next VMA. Poking parent VMAs and sharing their anon_vma is safe for now but is not expected behavior.
Note: this will break commit 4e4a9eb92133 ("mm/rmap.c: reuse mergeable anon_vma as parent when fork") without related fix because it contains several flaws hidden by current initialization sequence in dup_mmap().
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> --- kernel/fork.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c index c33626993831..784c9ae56aa9 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -544,10 +544,12 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, tmp = vm_area_dup(mpnt); if (!tmp) goto fail_nomem; + tmp->vm_mm = mm; + tmp->vm_prev = prev; + tmp->vm_next = NULL; retval = vma_dup_policy(mpnt, tmp); if (retval) goto fail_nomem_policy; - tmp->vm_mm = mm; retval = dup_userfaultfd(tmp, &uf); if (retval) goto fail_nomem_anon_vma_fork; @@ -559,7 +561,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, } else if (anon_vma_fork(tmp, mpnt, prev)) goto fail_nomem_anon_vma_fork; tmp->vm_flags &= ~(VM_LOCKED | VM_LOCKONFAULT); - tmp->vm_next = tmp->vm_prev = NULL; file = tmp->vm_file; if (file) { struct inode *inode = file_inode(file); @@ -592,7 +593,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, */ *pprev = tmp; pprev = &tmp->vm_next; - tmp->vm_prev = prev; prev = tmp; __vma_link_rb(mm, tmp, rb_link, rb_parent);
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