comedi: Flush partial mappings in error case

stable inclusion
from stable-v6.6.64
commit 9b07fb464eb69a752406e78e62ab3a60bfa7b00d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IBL4B6

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9b07fb464eb69a752406e78e62ab3a60bfa7b00d

--------------------------------

commit ce8f9fb651fac95dd41f69afe54d935420b945bd upstream.

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 error path.

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

Cc: [email protected]
Fixes: ed9eccb ("Staging: add comedi core")
Signed-off-by: Jann Horn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Wen Zhiwei <[email protected]>

Author: thejh

drivers/comedi/comedi_fops.c

@@ -2407,6 +2407,18 @@ static int comedi_mmap(struct file *file, struct vm_area_struct *vma)
 
 			start += PAGE_SIZE;
 		}
+
+#ifdef CONFIG_MMU
+		/*
+		 * 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.
+		 */
+		if (retval)
+			zap_vma_ptes(vma, vma->vm_start, size);
+#endif
 	}
 
 	if (retval == 0) {