[PATCH 6.6.y] mm: unconditionally close VMAs on error

[Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>]

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@xxxxxxxxxx>
Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
Cc: stable <stable@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reviewed-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
 mm/internal.h | 18 ++++++++++++++++++
 mm/mmap.c     |  9 +++------
 mm/nommu.c    |  3 +--
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index d52d6b57dafb..36c6693f4ebf 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -110,6 +110,24 @@ 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;
+	}
+}
+
 void __acct_reclaim_writeback(pg_data_t *pgdat, struct folio *folio,
 						int nr_throttled);
 static inline void acct_reclaim_writeback(struct folio *folio)
diff --git a/mm/mmap.c b/mm/mmap.c
index 8a055bae6bdb..9fefd13640d1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -137,8 +137,7 @@ void unlink_file_vma(struct vm_area_struct *vma)
 static void remove_vma(struct vm_area_struct *vma, bool unreachable)
 {
 	might_sleep();
-	if (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));
@@ -2899,8 +2898,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	return addr;
 
 close_and_free_vma:
-	if (file && vma->vm_ops && vma->vm_ops->close)
-		vma->vm_ops->close(vma);
+	vma_close(vma);
 
 	if (file || vma->vm_file) {
 unmap_and_free_vma:
@@ -3392,8 +3390,7 @@ 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/nommu.c b/mm/nommu.c
index e976c62264c9..8bc339050e6d 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -600,8 +600,7 @@ 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);
-- 
2.47.0