From 79f3d123caedbac30a6fd75f9597b2a60a89d513 Mon Sep 17 00:00:00 2001 From: "Liam R. Howlett" Date: Tue, 15 Oct 2024 21:34:55 -0400 Subject: [PATCH] mm/mmap: fix race in mmap_region() with ftruncate() Avoiding the zeroing of the vma tree in mmap_region() introduced a race with truncate in the page table walk. To avoid any races, create a hole in the rmap during the operation by clearing the pagetable entries earlier under the mmap write lock and (critically) before the new vma is installed into the vma tree. The result is that the old vma(s) are left in the vma tree, but free_pgtables() removes them from the rmap and clears the ptes while holding the necessary locks. This change extends the fix required for hugetblfs and the call_mmap() function by moving the cleanup higher in the function and running it unconditionally. Link: https://lkml.kernel.org/r/20241016013455.2241533-1-Liam.Howlett@oracle.com Fixes: f8d112a4e657 ("mm/mmap: avoid zeroing vma tree in mmap_region()") Signed-off-by: Liam R. Howlett Reported-by: Jann Horn Closes: https://lore.kernel.org/all/CAG48ez0ZpGzxi=-5O_uGQ0xKXOmbjeQ0LjZsRJ1Qtf2X5eOr1w@mail.gmail.com/ Reviewed-by: Jann Horn Reviewed-by: Lorenzo Stoakes Acked-by: Vlastimil Babka Cc: Matthew Wilcox Cc: David Hildenbrand Signed-off-by: Andrew Morton --- mm/mmap.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 9c0fb43064b5..3f1419460be3 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1418,6 +1418,13 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vmg.flags = vm_flags; } + /* + * clear PTEs while the vma is still in the tree so that rmap + * cannot race with the freeing later in the truncate scenario. + * This is also needed for call_mmap(), which is why vm_ops + * close function is called. + */ + vms_clean_up_area(&vms, &mas_detach); vma = vma_merge_new_range(&vmg); if (vma) goto expanded; @@ -1439,11 +1446,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr, if (file) { vma->vm_file = get_file(file); - /* - * call_mmap() may map PTE, so ensure there are no existing PTEs - * and call the vm_ops close function if one exists. - */ - vms_clean_up_area(&vms, &mas_detach); error = call_mmap(file, vma); if (error) goto unmap_and_free_vma;