vma: detect infinite loop in vma tree

There have been no reported infinite loops in the tree, but checking the
detection of an infinite loop during validation is simple enough.  Add the
detection to the validate_mm() function so that error reports are clear
and don't just report stalls.

This does not protect against internal maple tree issues, but it does
detect too many vmas being returned from the tree.

The variance of +10 is to allow for the debugging output to be more useful
for nearly correct counts.  In the event of more than 10 over the
map_count, the count will be set to -1 for easier identification of a
potential infinite loop.

Note that the mmap lock is held to ensure a consistent tree state during
the validation process.

Link: https://lkml.kernel.org/r/20241031193608.1965366-1-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vma.c b/mm/vma.c
index 68138e8c153e67df2baf3ac7315354578339dece..283e6bc4884f3ef6f6e3a8de87e60082af8007b4 100644 (file)
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -615,7 +615,10 @@ void validate_mm(struct mm_struct *mm)
                        anon_vma_unlock_read(anon_vma);
                }
 #endif
-               i++;
+               if (++i > mm->map_count + 10) {
+                       i = -1;
+                       break;
+               }
        }
        if (i != mm->map_count) {
                pr_emerg("map_count %d vma iterator %d\n", mm->map_count, i);