[PATCH 5.15.y 2/4] mm: unconditionally close VMAs on error

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

[ Upstream commit 4080ef1579b2413435413988d14ac8c68e4d42c8 ]

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.

Link: https://lkml.kernel.org/r/28e89dda96f68c505cb6f8e9fc9b57c3e9f74b42.1730224667.git.lorenzo.stoakes@oracle.com
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: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
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>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 mm/internal.h |  7 +++++++
 mm/mmap.c     |  9 +++------
 mm/nommu.c    |  3 +--
 mm/util.c     | 15 +++++++++++++++
 4 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 4670e97eb694..34b3a16aa01f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -46,6 +46,13 @@ void page_writeback_init(void);
  */
 int mmap_file(struct file *file, struct vm_area_struct *vma);
 
+/*
+ * 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.
+ */
+void vma_close(struct vm_area_struct *vma);
+
 vm_fault_t do_swap_page(struct vm_fault *vmf);
 
 void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
diff --git a/mm/mmap.c b/mm/mmap.c
index 11d023eab949..d19fdcf2aa26 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -180,8 +180,7 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
 	struct vm_area_struct *next = vma->vm_next;
 
 	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));
@@ -1877,8 +1876,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	return addr;
 
 close_and_free_vma:
-	if (vma->vm_ops && vma->vm_ops->close)
-		vma->vm_ops->close(vma);
+	vma_close(vma);
 unmap_and_free_vma:
 	fput(vma->vm_file);
 	vma->vm_file = NULL;
@@ -2762,8 +2760,7 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
 		return 0;
 
 	/* Clean everything up if vma_adjust failed. */
-	if (new->vm_ops && new->vm_ops->close)
-		new->vm_ops->close(new);
+	vma_close(new);
 	if (new->vm_file)
 		fput(new->vm_file);
 	unlink_anon_vmas(new);
diff --git a/mm/nommu.c b/mm/nommu.c
index 2515c98d4be1..084dd593913e 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -652,8 +652,7 @@ static void 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/util.c b/mm/util.c
index f55d7be982de..af6c9bce8314 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1104,6 +1104,21 @@ int mmap_file(struct file *file, struct vm_area_struct *vma)
 	return err;
 }
 
+void vma_close(struct vm_area_struct *vma)
+{
+	static const struct vm_operations_struct dummy_vm_ops = {};
+
+	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 = &dummy_vm_ops;
+	}
+}
+
 #ifdef CONFIG_PRINTK
 /**
  * mem_dump_obj - Print available provenance information
-- 
2.47.0