The MREMAP_DONTUNMAP feature is highly unusual in that it permits mremap() operations that keep the original VMA in place. Historically this has led to a lot of bugs where non-obvious interactions occur between existing mremap() operations and the original VMA. Fix another of these - self-merge. Self-merge occurs when a VMA is moved in front of or behind itself and the attributes of the VMA permit such a merge. Practically this can only happen for unfaulted anonymous VMAs due to the page offset equality requirement for merge: |------------| | | | v |...........||-----------||...........| | || unfaulted || | |...........||-----------||...........| ^ | | | |------------| This becomes problematic if the VMA is configured by the user to mlock-on-fault, i.e. the VMA_LOCKED_BIT, VMA_LOCKONFAULT_BIT VMA flags are set. MREMAP_DONTUNMAP clears mlock flags for the source VMA and maintains them for the destination VMA. Self-merge makes this impossible (there is only one VMA) and incorrectly clears the destination VMA's mlock flags. This causes a leak in mm->locked_vm as clearing this flag does not decrement the counter and the VMA no longer has VMA_LOCKED_BIT set so it is not decremented on unmap. Resolve this by simply disallowing a self-merge in this case - the source and destination VMAs are kept distinct and then are able to have distinct mlock() flags. Update dontunmap_complete() to make the now-redundant self-merge check a VM_WARN_ON_ONCE() instead to guard against future regressions. Also update the VMA userland tests to reflect the change. Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()") Cc: stable@vger.kernel.org Reviewed-by: Pedro Falcato Acked-by: Kiryl Shutsemau (Meta) Reviewed-by: Jose A. Perez de Azpillaga Signed-off-by: Lorenzo Stoakes (ARM) --- mm/mremap.c | 8 ++++++-- mm/vma.c | 17 ++++++++++++++++- mm/vma.h | 2 +- tools/testing/vma/tests/vma.c | 10 +++++----- 4 files changed, 28 insertions(+), 9 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 1122282a1d6a..73f52c45705c 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -1275,7 +1275,8 @@ static int copy_vma_and_data(struct vma_remap_struct *vrm, PAGETABLE_MOVE(pmc, NULL, NULL, vrm->addr, vrm->new_addr, vrm->old_len); new_vma = copy_vma(&vma, vrm->new_addr, vrm->new_len, new_pgoff, - new_anon_pgoff, &pmc.need_rmap_locks); + new_anon_pgoff, &pmc.need_rmap_locks, + vrm->flags & MREMAP_DONTUNMAP); if (!new_vma) { vrm_uncharge(vrm); *new_vma_ptr = NULL; @@ -1335,6 +1336,9 @@ static void dontunmap_complete(struct vma_remap_struct *vrm, unsigned long old_start = vma->vm_start; unsigned long old_end = vma->vm_end; + /* Self-merge is disallowed. */ + VM_WARN_ON_ONCE(new_vma == vma); + /* We always clear VMA_LOCKED[ONFAULT]_BIT on the old VMA. */ vma_clear_flags_mask(vma, VMA_LOCKED_MASK); @@ -1342,7 +1346,7 @@ static void dontunmap_complete(struct vma_remap_struct *vrm, * anon_vma links of the old vma is no longer needed after its page * table has been moved. */ - if (new_vma != vma && start == old_start && end == old_end) { + if (start == old_start && end == old_end) { const pgoff_t pgoff_unfaulted = vma->vm_start >> PAGE_SHIFT; unlink_anon_vmas(vma); diff --git a/mm/vma.c b/mm/vma.c index 0db3f1222cad..55d4d0939129 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -1946,7 +1946,7 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) */ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, unsigned long addr, unsigned long len, pgoff_t pgoff, - pgoff_t anon_pgoff, bool *need_rmap_locks) + pgoff_t anon_pgoff, bool *need_rmap_locks, bool keep_source) { struct vm_area_struct *vma = *vmap; unsigned long old_vma_start = vma->vm_start; @@ -1984,6 +1984,21 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, vmg.pgoff = pgoff; vmg.anon_pgoff = anon_pgoff; vmg.next = vma_iter_next_rewind(&vmi, NULL); + + /* + * If the original VMA is kept (MREMAP_DONTUNMAP), the source and + * destination VMA must be treated distinctly. + * + * A merge violates this, so in this case disallow a self-merge. + */ + if (can_self_merge && keep_source) { + if (vmg.prev == vma) + vmg.prev = NULL; + if (vmg.next == vma) + vmg.next = NULL; + can_self_merge = false; + } + new_vma = vma_merge_copied_range(&vmg); if (new_vma) { diff --git a/mm/vma.h b/mm/vma.h index b2c3bc832a48..03ed8afd0c1f 100644 --- a/mm/vma.h +++ b/mm/vma.h @@ -534,7 +534,7 @@ void unlink_file_vma_batch_add(struct unlink_vma_file_batch *vb, struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, unsigned long addr, unsigned long len, pgoff_t pgoff, - pgoff_t anon_pgoff, bool *need_rmap_locks); + pgoff_t anon_pgoff, bool *need_rmap_locks, bool keep_source); struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma); diff --git a/tools/testing/vma/tests/vma.c b/tools/testing/vma/tests/vma.c index c8ef7b8cd46b..e973e0a6d1a8 100644 --- a/tools/testing/vma/tests/vma.c +++ b/tools/testing/vma/tests/vma.c @@ -40,7 +40,7 @@ static bool test_copy_vma(void) vma = alloc_and_link_vma(&mm, 0x1000, 0x2000, 1, vma_flags); vma_set_anonymous(vma); vma_orig = vma; - vma_new = copy_vma(&vma, 0x2000, 0x1000, 1, 1, &need_locks); + vma_new = copy_vma(&vma, 0x2000, 0x1000, 1, 1, &need_locks, false); ASSERT_EQ(vma_new, vma_orig); ASSERT_EQ(vma, vma_orig); ASSERT_EQ(vma_new->vm_start, 0x1000); @@ -53,7 +53,7 @@ static bool test_copy_vma(void) vma = alloc_and_link_vma(&mm, 0x2000, 0x3000, 2, vma_flags); vma_set_anonymous(vma); vma_orig = vma; - vma_new = copy_vma(&vma, 0x1000, 0x1000, 2, 2, &need_locks); + vma_new = copy_vma(&vma, 0x1000, 0x1000, 2, 2, &need_locks, false); ASSERT_EQ(vma_new, vma_orig); ASSERT_EQ(vma, vma_orig); ASSERT_EQ(vma_new->vm_start, 0x1000); @@ -71,7 +71,7 @@ static bool test_copy_vma(void) vma = alloc_and_link_vma(&mm, 0x3000, 0x4000, 3, vma_flags); vma_set_anonymous(vma); vma_orig = vma; - vma_new = copy_vma(&vma, 0x2000, 0x1000, 3, 3, &need_locks); + vma_new = copy_vma(&vma, 0x2000, 0x1000, 3, 3, &need_locks, false); ASSERT_NE(vma_new, vma_orig); ASSERT_EQ(vma_new, vma); ASSERT_EQ(vma_new->vm_start, 0x1000); @@ -82,7 +82,7 @@ static bool test_copy_vma(void) /* Move backwards and do not merge. */ vma = alloc_and_link_vma(&mm, 0x3000, 0x5000, 3, vma_flags); - vma_new = copy_vma(&vma, 0, 0x2000, 0, 3, &need_locks); + vma_new = copy_vma(&vma, 0, 0x2000, 0, 3, &need_locks, false); ASSERT_NE(vma_new, vma); ASSERT_EQ(vma_new->vm_start, 0); ASSERT_EQ(vma_new->vm_end, 0x2000); @@ -95,7 +95,7 @@ static bool test_copy_vma(void) vma = alloc_and_link_vma(&mm, 0, 0x2000, 0, vma_flags); vma_next = alloc_and_link_vma(&mm, 0x6000, 0x8000, 6, vma_flags); - vma_new = copy_vma(&vma, 0x4000, 0x2000, 4, 4, &need_locks); + vma_new = copy_vma(&vma, 0x4000, 0x2000, 4, 4, &need_locks, false); vma_assert_attached(vma_new); ASSERT_EQ(vma_new, vma_next); -- 2.55.0