diff options
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/mremap.c | 17 |
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; |