On 14/10/2024 21:50, Jann Horn wrote:
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
Your patched version won't compile before 6.1 so you may want to
indicate that in the Cc line.
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
I guess this doesn't need to be done for the path that calls
dma_mmap_coherent() since that does not do any range splitting. Would it
be better to move it into the branch that calls remap_pfn_range() in a loop?
Note that I have no commit access to pulled-from repositories. Greg-KH
usually commits them on one of his repos, so could you Cc him too? Thanks.
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