[PATCH] comedi: Flush partial mappings in error case

[Jann Horn]

If some remap_pfn_range() calls succeeded before one failed, we still have
buffer pages mapped into the userspace page tables when we drop the buffer
reference with comedi_buf_map_put(bm). The userspace mappings are only
cleaned up later in the mmap error path.

Fix it by explicitly flushing all mappings in our VMA on the comedi_mmap()
error path.

See commit 79a61cc3fc04 ("mm: avoid leaving partial pfn mappings around in
error case").

Cc: stable@xxxxxxxxxxxxxxx
Fixes: ed9eccbe8970 ("Staging: add comedi core")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
Note: compile-tested only; I don't actually have comedi hardware, and I
don't know anything about comedi.
---
 drivers/comedi/comedi_fops.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
index 1b481731df96..0e573df8646f 100644
--- a/drivers/comedi/comedi_fops.c
+++ b/drivers/comedi/comedi_fops.c
@@ -2414,6 +2414,15 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 		vma->vm_private_data = bm;
 
 		vma->vm_ops->open(vma);
+	} else {
+		/*
+		 * Leaving behind a partial mapping of a buffer we're about to
+		 * drop is unsafe, see remap_pfn_range_notrack().
+		 * We need to zap the range here ourselves instead of relying
+		 * on the automatic zapping in remap_pfn_range() because we call
+		 * remap_pfn_range() in a loop.
+		 */
+		zap_page_range_single(vma, vma->vm_start, size, NULL);
 	}
 
 done:

---
base-commit: 6485cf5ea253d40d507cd71253c9568c5470cd27
change-id: 20241014-comedi-tlb-400246505961
-- 
Jann Horn <jannh@xxxxxxxxxx>