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Diffstat (limited to 'mm')
-rw-r--r--mm/mremap.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/mm/mremap.c b/mm/mremap.c
index 3320616ed93f..e3edef6b7a12 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -516,6 +516,23 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
if (addr + old_len > new_addr && new_addr + new_len > addr)
goto out;
+ /*
+ * move_vma() need us to stay 4 maps below the threshold, otherwise
+ * it will bail out at the very beginning.
+ * That is a problem if we have already unmaped the regions here
+ * (new_addr, and old_addr), because userspace will not know the
+ * state of the vma's after it gets -ENOMEM.
+ * So, to avoid such scenario we can pre-compute if the whole
+ * operation has high chances to success map-wise.
+ * Worst-scenario case is when both vma's (new_addr and old_addr) get
+ * split in 3 before unmaping it.
+ * That means 2 more maps (1 for each) to the ones we already hold.
+ * Check whether current map count plus 2 still leads us to 4 maps below
+ * the threshold, otherwise return -ENOMEM here to be more safe.
+ */
+ if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
+ return -ENOMEM;
+
ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
if (ret)
goto out;