[PATCH v3 4/7] mm/mremap: Replace can_modify_mm with can_modify_vma

[Pedro Falcato <pedro.falcato@gmail.com>]

Delegate all can_modify checks to the proper places. Unmap checks are
done in do_unmap (et al). The source VMA check is done purposefully
before unmapping, to keep the original mseal semantics.

Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
---
 mm/mremap.c | 32 ++++++--------------------------
 1 file changed, 6 insertions(+), 26 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index e7ae140fc640..24712f8dbb6b 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -902,19 +902,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 	if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 		return -ENOMEM;
 
-	/*
-	 * In mremap_to().
-	 * Move a VMA to another location, check if src addr is sealed.
-	 *
-	 * Place can_modify_mm here because mremap_to()
-	 * does its own checking for address range, and we only
-	 * check the sealing after passing those checks.
-	 *
-	 * can_modify_mm assumes we have acquired the lock on MM.
-	 */
-	if (unlikely(!can_modify_mm(mm, addr, addr + old_len)))
-		return -EPERM;
-
 	if (flags & MREMAP_FIXED) {
 		/*
 		 * In mremap_to().
@@ -1052,6 +1039,12 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 		goto out;
 	}
 
+	/* Don't allow remapping vmas when they have already been sealed */
+	if (!can_modify_vma(vma)) {
+		ret = -EPERM;
+		goto out;
+	}
+
 	if (is_vm_hugetlb_page(vma)) {
 		struct hstate *h __maybe_unused = hstate_vma(vma);
 
@@ -1079,19 +1072,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 		goto out;
 	}
 
-	/*
-	 * Below is shrink/expand case (not mremap_to())
-	 * Check if src address is sealed, if so, reject.
-	 * In other words, prevent shrinking or expanding a sealed VMA.
-	 *
-	 * Place can_modify_mm here so we can keep the logic related to
-	 * shrink/expand together.
-	 */
-	if (unlikely(!can_modify_mm(mm, addr, addr + old_len))) {
-		ret = -EPERM;
-		goto out;
-	}
-
 	/*
 	 * Always allow a shrinking remap: that just unmaps
 	 * the unnecessary pages..

-- 
2.46.0