The patch titled Subject: mm: avoid unsafe VMA hook invocation when error arises on mmap hook has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> Subject: mm: avoid unsafe VMA hook invocation when error arises on mmap hook Date: Tue, 22 Oct 2024 21:40:52 +0100 Patch series "fix error handling in mmap_region() and refactor". mmap_region() is somewhat terrifying, with spaghetti-like control flow and numerous means by which issues can arise and incomplete state, memory leaks and other unpleasantness can occur. A large amount of the complexity arises from trying to handle errors late in the process of mapping a VMA, which forms the basis of recently observed issues with resource leaks and observable inconsistent state. This series goes to great lengths to simplify how mmap_region() works and to avoid unwinding errors late on in the process of setting up the VMA for the new mapping, and equally avoids such operations occurring while the VMA is in an inconsistent state. The first four patches are intended for backporting to correct the possibility of people encountering corrupted state while invoking mmap() which is otherwise at risk of happening. After this we go further, refactoring the code, placing it in mm/vma.c in order to make it eventually userland testable, and significantly simplifying the logic to avoid this issue arising in future. This patch (of 8): After an attempted mmap() fails, we are no longer in a situation where we can safely interact with VMA hooks. This is currently not enforced, meaning that we need complicated handling to ensure we do not incorrectly call these hooks. We can avoid the whole issue by treating the VMA as suspect the moment that the file->f_ops->mmap() function reports an error by replacing whatever VMA operations were installed with a dummy empty set of VMA operations. We do so through a new helper function internal to mm - mmap_file() - which is both more logically named than the existing call_mmap() function and correctly isolates handling of the vm_op reassignment to mm. All the existing invocations of call_mmap() outside of mm are ultimately nested within the call_mmap() from mm, which we now replace. It is therefore safe to leave call_mmap() in place as a convenience function (and to avoid churn). The invokers are: ovl_file_operations -> mmap -> ovl_mmap() -> backing_file_mmap() coda_file_operations -> mmap -> coda_file_mmap() shm_file_operations -> shm_mmap() shm_file_operations_huge -> shm_mmap() dma_buf_fops -> dma_buf_mmap_internal -> i915_dmabuf_ops -> i915_gem_dmabuf_mmap() None of these callers interact with vm_ops or mappings in a problematic way on error, quickly exiting out. Link: https://lkml.kernel.org/r/cover.1729628198.git.lorenzo.stoakes@xxxxxxxxxx Link: https://lkml.kernel.org/r/ddc1e43edbb1e8717c2be7fde96b682d8a898836.1729628198.git.lorenzo.stoakes@xxxxxxxxxx Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails") Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> Reported-by: Jann Horn <jannh@xxxxxxxxxx> Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: <stable@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/internal.h | 27 +++++++++++++++++++++++++++ mm/mmap.c | 6 +++--- mm/nommu.c | 4 ++-- 3 files changed, 32 insertions(+), 5 deletions(-) --- a/mm/internal.h~mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook +++ a/mm/internal.h @@ -108,6 +108,33 @@ static inline void *folio_raw_mapping(co return (void *)(mapping & ~PAGE_MAPPING_FLAGS); } +/* + * This is a file-backed mapping, and is about to be memory mapped - invoke its + * mmap hook and safely handle error conditions. On error, VMA hooks will be + * mutated. + * + * @file: File which backs the mapping. + * @vma: VMA which we are mapping. + * + * Returns: 0 if success, error otherwise. + */ +static inline int mmap_file(struct file *file, struct vm_area_struct *vma) +{ + int err = call_mmap(file, vma); + + if (likely(!err)) + return 0; + + /* + * OK, we tried to call the file hook for mmap(), but an error + * arose. The mapping is in an inconsistent state and we most not invoke + * any further hooks on it. + */ + vma->vm_ops = &vma_dummy_vm_ops; + + return err; +} + #ifdef CONFIG_MMU /* Flags for folio_pte_batch(). */ --- a/mm/mmap.c~mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook +++ a/mm/mmap.c @@ -1421,7 +1421,7 @@ unsigned long mmap_region(struct file *f /* * 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 + * This is also needed for mmap_file(), which is why vm_ops * close function is called. */ vms_clean_up_area(&vms, &mas_detach); @@ -1446,7 +1446,7 @@ unsigned long mmap_region(struct file *f if (file) { vma->vm_file = get_file(file); - error = call_mmap(file, vma); + error = mmap_file(file, vma); if (error) goto unmap_and_free_vma; @@ -1469,7 +1469,7 @@ unsigned long mmap_region(struct file *f vma_iter_config(&vmi, addr, end); /* - * If vm_flags changed after call_mmap(), we should try merge + * If vm_flags changed after mmap_file(), we should try merge * vma again as we may succeed this time. */ if (unlikely(vm_flags != vma->vm_flags && vmg.prev)) { --- a/mm/nommu.c~mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook +++ a/mm/nommu.c @@ -885,7 +885,7 @@ static int do_mmap_shared_file(struct vm { int ret; - ret = call_mmap(vma->vm_file, vma); + ret = mmap_file(vma->vm_file, vma); if (ret == 0) { vma->vm_region->vm_top = vma->vm_region->vm_end; return 0; @@ -918,7 +918,7 @@ static int do_mmap_private(struct vm_are * happy. */ if (capabilities & NOMMU_MAP_DIRECT) { - ret = call_mmap(vma->vm_file, vma); + ret = mmap_file(vma->vm_file, vma); /* shouldn't return success if we're not sharing */ if (WARN_ON_ONCE(!is_nommu_shared_mapping(vma->vm_flags))) ret = -ENOSYS; _ Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are fork-do-not-invoke-uffd-on-fork-if-error-occurs.patch fork-only-invoke-khugepaged-ksm-hooks-if-no-error.patch mm-vma-add-expand-only-vma-merge-mode-and-optimise-do_brk_flags.patch tools-testing-add-expand-only-mode-vma-test.patch mm-avoid-unsafe-vma-hook-invocation-when-error-arises-on-mmap-hook.patch mm-unconditionally-close-vmas-on-error.patch mm-refactor-map_deny_write_exec.patch mm-resolve-faulty-mmap_region-error-path-behaviour.patch tools-testing-add-additional-vma_internalh-stubs.patch mm-insolate-mmap-internal-logic-to-mm-vmac.patch mm-refactor-__mmap_region.patch mm-do-not-attempt-second-merge-for-file-backed-vmas.patch selftests-mm-add-pkey_sighandler_xx-hugetlb_dio-to-gitignore.patch mm-refactor-mm_access-to-not-return-null.patch mm-refactor-mm_access-to-not-return-null-fix.patch mm-madvise-unrestrict-process_madvise-for-current-process.patch maple_tree-do-not-hash-pointers-on-dump-in-debug-mode.patch tools-testing-fix-phys_addr_t-size-on-64-bit-systems.patch