The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x 3dd6ed34ce1f2356a77fb88edafb5ec96784e3cf # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024111146-visiting-designing-ea20@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3dd6ed34ce1f2356a77fb88edafb5ec96784e3cf Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes lorenzo.stoakes@oracle.com Date: Tue, 29 Oct 2024 18:11:44 +0000 Subject: [PATCH] mm: avoid unsafe VMA hook invocation when error arises on mmap hook

Patch series "fix error handling in mmap_region() and refactor (hotfixes)", v4.

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 patches in this series comprise the minimal changes required to resolve existing issues in mmap_region() error handling, in order that they can be hotfixed and backported. There is additionally a follow up series which goes further, separated out from the v1 series and sent and updated separately.

This patch (of 5):

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.1730224667.git.lorenzo.stoakes@oracle.com Link: https://lkml.kernel.org/r/d41fd763496fd0048a962f3fd9407dc72dd4fd86.173022466... Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails") Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Reported-by: Jann Horn jannh@google.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Jann Horn jannh@google.com Cc: Andreas Larsson andreas@gaisler.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: David S. Miller davem@davemloft.net Cc: Helge Deller deller@gmx.de Cc: James E.J. Bottomley James.Bottomley@HansenPartnership.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Mark Brown broonie@kernel.org Cc: Peter Xu peterx@redhat.com Cc: Will Deacon will@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org

diff --git a/mm/internal.h b/mm/internal.h index 16c1f3cd599e..4eab2961e69c 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -108,6 +108,33 @@ static inline void *folio_raw_mapping(const struct folio *folio) 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(). */ diff --git a/mm/mmap.c b/mm/mmap.c index 9841b41e3c76..6e3b25f7728f 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1422,7 +1422,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, /* * 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); @@ -1447,7 +1447,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,

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;

@@ -1470,7 +1470,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,

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)) { diff --git a/mm/nommu.c b/mm/nommu.c index 385b0c15add8..f9ccc02458ec 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -885,7 +885,7 @@ static int do_mmap_shared_file(struct vm_area_struct *vma) { 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_area_struct *vma, * 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;