[PATCH hotfix 6.12 v4 2/5] mm: unconditionally close VMAs on error

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Incorrect invocation of VMA callbacks when the VMA is no longer in a
consistent state is bug prone and risky to perform.

With regards to the important vm_ops->close() callback We have gone to
great lengths to try to track whether or not we ought to close VMAs.

Rather than doing so and risking making a mistake somewhere, instead
unconditionally close and reset vma->vm_ops to an empty dummy operations
set with a NULL .close operator.

We introduce a new function to do so - vma_close() - and simplify existing
vms logic which tracked whether we needed to close or not.

This simplifies the logic, avoids incorrect double-calling of the .close()
callback and allows us to update error paths to simply call vma_close()
unconditionally - making VMA closure idempotent.

Reported-by: Jann Horn <jannh@google.com>
Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
Cc: stable <stable@kernel.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 mm/internal.h | 18 ++++++++++++++++++
 mm/mmap.c     |  5 ++---
 mm/nommu.c    |  3 +--
 mm/vma.c      | 14 +++++---------
 mm/vma.h      |  4 +---
 5 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 4eab2961e69c..64c2eb0b160e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -135,6 +135,24 @@ static inline int mmap_file(struct file *file, struct vm_area_struct *vma)
 	return err;
 }

+/*
+ * If the VMA has a close hook then close it, and since closing it might leave
+ * it in an inconsistent state which makes the use of any hooks suspect, clear
+ * them down by installing dummy empty hooks.
+ */
+static inline void vma_close(struct vm_area_struct *vma)
+{
+	if (vma->vm_ops && vma->vm_ops->close) {
+		vma->vm_ops->close(vma);
+
+		/*
+		 * The mapping is in an inconsistent state, and no further hooks
+		 * may be invoked upon it.
+		 */
+		vma->vm_ops = &vma_dummy_vm_ops;
+	}
+}
+
 #ifdef CONFIG_MMU

 /* Flags for folio_pte_batch(). */
diff --git a/mm/mmap.c b/mm/mmap.c
index 6e3b25f7728f..ac0604f146f6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1573,8 +1573,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	return addr;

 close_and_free_vma:
-	if (file && !vms.closed_vm_ops && vma->vm_ops && vma->vm_ops->close)
-		vma->vm_ops->close(vma);
+	vma_close(vma);

 	if (file || vma->vm_file) {
 unmap_and_free_vma:
@@ -1934,7 +1933,7 @@ void exit_mmap(struct mm_struct *mm)
 	do {
 		if (vma->vm_flags & VM_ACCOUNT)
 			nr_accounted += vma_pages(vma);
-		remove_vma(vma, /* unreachable = */ true, /* closed = */ false);
+		remove_vma(vma, /* unreachable = */ true);
 		count++;
 		cond_resched();
 		vma = vma_next(&vmi);
diff --git a/mm/nommu.c b/mm/nommu.c
index f9ccc02458ec..635d028d647b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -589,8 +589,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma)
  */
 static void delete_vma(struct mm_struct *mm, struct vm_area_struct *vma)
 {
-	if (vma->vm_ops && vma->vm_ops->close)
-		vma->vm_ops->close(vma);
+	vma_close(vma);
 	if (vma->vm_file)
 		fput(vma->vm_file);
 	put_nommu_region(vma->vm_region);
diff --git a/mm/vma.c b/mm/vma.c
index b21ffec33f8e..7621384d64cf 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -323,11 +323,10 @@ static bool can_vma_merge_right(struct vma_merge_struct *vmg,
 /*
  * Close a vm structure and free it.
  */
-void remove_vma(struct vm_area_struct *vma, bool unreachable, bool closed)
+void remove_vma(struct vm_area_struct *vma, bool unreachable)
 {
 	might_sleep();
-	if (!closed && vma->vm_ops && vma->vm_ops->close)
-		vma->vm_ops->close(vma);
+	vma_close(vma);
 	if (vma->vm_file)
 		fput(vma->vm_file);
 	mpol_put(vma_policy(vma));
@@ -1115,9 +1114,7 @@ void vms_clean_up_area(struct vma_munmap_struct *vms,
 	vms_clear_ptes(vms, mas_detach, true);
 	mas_set(mas_detach, 0);
 	mas_for_each(mas_detach, vma, ULONG_MAX)
-		if (vma->vm_ops && vma->vm_ops->close)
-			vma->vm_ops->close(vma);
-	vms->closed_vm_ops = true;
+		vma_close(vma);
 }

 /*
@@ -1160,7 +1157,7 @@ void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
 	/* Remove and clean up vmas */
 	mas_set(mas_detach, 0);
 	mas_for_each(mas_detach, vma, ULONG_MAX)
-		remove_vma(vma, /* = */ false, vms->closed_vm_ops);
+		remove_vma(vma, /* unreachable = */ false);

 	vm_unacct_memory(vms->nr_accounted);
 	validate_mm(mm);
@@ -1684,8 +1681,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	return new_vma;

 out_vma_link:
-	if (new_vma->vm_ops && new_vma->vm_ops->close)
-		new_vma->vm_ops->close(new_vma);
+	vma_close(new_vma);

 	if (new_vma->vm_file)
 		fput(new_vma->vm_file);
diff --git a/mm/vma.h b/mm/vma.h
index 55457cb68200..75558b5e9c8c 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -42,7 +42,6 @@ struct vma_munmap_struct {
 	int vma_count;                  /* Number of vmas that will be removed */
 	bool unlock;                    /* Unlock after the munmap */
 	bool clear_ptes;                /* If there are outstanding PTE to be cleared */
-	bool closed_vm_ops;		/* call_mmap() was encountered, so vmas may be closed */
 	/* 1 byte hole */
 	unsigned long nr_pages;         /* Number of pages being removed */
 	unsigned long locked_vm;        /* Number of locked pages */
@@ -198,7 +197,6 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms,
 	vms->unmap_start = FIRST_USER_ADDRESS;
 	vms->unmap_end = USER_PGTABLES_CEILING;
 	vms->clear_ptes = false;
-	vms->closed_vm_ops = false;
 }
 #endif

@@ -269,7 +267,7 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
 		  unsigned long start, size_t len, struct list_head *uf,
 		  bool unlock);

-void remove_vma(struct vm_area_struct *vma, bool unreachable, bool closed);
+void remove_vma(struct vm_area_struct *vma, bool unreachable);

 void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct vm_area_struct *next);
--
2.47.0