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SubjectRe: [PATCH] mm: Add MREMAP_DONTUNMAP to mremap().
Hi Brian,

url: https://github.com/0day-ci/linux/commits/Brian-Geffon/mm-Add-MREMAP_DONTUNMAP-to-mremap/20200125-013342
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 4703d9119972bf586d2cca76ec6438f819ffa30e

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>

smatch warnings:
mm/mremap.c:561 mremap_to() error: potentially dereferencing uninitialized 'vma'.

# https://github.com/0day-ci/linux/commit/98663ca05501623c3da7f0f30be8ba7d632cf010
git remote add linux-review https://github.com/0day-ci/linux
git remote update linux-review
git checkout 98663ca05501623c3da7f0f30be8ba7d632cf010
vim +/vma +561 mm/mremap.c

81909b842107ef Michel Lespinasse 2013-02-22 506 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
72f87654c69690 Pavel Emelyanov 2017-02-22 507 unsigned long new_addr, unsigned long new_len, bool *locked,
98663ca0550162 Brian Geffon 2020-01-22 508 unsigned long flags, struct vm_userfaultfd_ctx *uf,
b22823719302e8 Mike Rapoport 2017-08-02 509 struct list_head *uf_unmap_early,
897ab3e0c49e24 Mike Rapoport 2017-02-24 510 struct list_head *uf_unmap)
ecc1a8993751de Al Viro 2009-11-24 511 {
ecc1a8993751de Al Viro 2009-11-24 512 struct mm_struct *mm = current->mm;
ecc1a8993751de Al Viro 2009-11-24 513 struct vm_area_struct *vma;
ecc1a8993751de Al Viro 2009-11-24 514 unsigned long ret = -EINVAL;
ecc1a8993751de Al Viro 2009-11-24 515 unsigned long charged = 0;
097eed103862f9 Al Viro 2009-11-24 516 unsigned long map_flags;
ecc1a8993751de Al Viro 2009-11-24 517
f19cb115a25f3f Alexander Kuleshov 2015-11-05 518 if (offset_in_page(new_addr))
ecc1a8993751de Al Viro 2009-11-24 519 goto out;
ecc1a8993751de Al Viro 2009-11-24 520
ecc1a8993751de Al Viro 2009-11-24 521 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
ecc1a8993751de Al Viro 2009-11-24 522 goto out;
ecc1a8993751de Al Viro 2009-11-24 523
9943242ca46814 Oleg Nesterov 2015-09-04 524 /* Ensure the old/new locations do not overlap */
9943242ca46814 Oleg Nesterov 2015-09-04 525 if (addr + old_len > new_addr && new_addr + new_len > addr)
ecc1a8993751de Al Viro 2009-11-24 526 goto out;
ecc1a8993751de Al Viro 2009-11-24 527
ea2c3f6f554561 Oscar Salvador 2019-03-05 528 /*
ea2c3f6f554561 Oscar Salvador 2019-03-05 529 * move_vma() need us to stay 4 maps below the threshold, otherwise
ea2c3f6f554561 Oscar Salvador 2019-03-05 530 * it will bail out at the very beginning.
ea2c3f6f554561 Oscar Salvador 2019-03-05 531 * That is a problem if we have already unmaped the regions here
ea2c3f6f554561 Oscar Salvador 2019-03-05 532 * (new_addr, and old_addr), because userspace will not know the
ea2c3f6f554561 Oscar Salvador 2019-03-05 533 * state of the vma's after it gets -ENOMEM.
ea2c3f6f554561 Oscar Salvador 2019-03-05 534 * So, to avoid such scenario we can pre-compute if the whole
ea2c3f6f554561 Oscar Salvador 2019-03-05 535 * operation has high chances to success map-wise.
ea2c3f6f554561 Oscar Salvador 2019-03-05 536 * Worst-scenario case is when both vma's (new_addr and old_addr) get
ea2c3f6f554561 Oscar Salvador 2019-03-05 537 * split in 3 before unmaping it.
ea2c3f6f554561 Oscar Salvador 2019-03-05 538 * That means 2 more maps (1 for each) to the ones we already hold.
ea2c3f6f554561 Oscar Salvador 2019-03-05 539 * Check whether current map count plus 2 still leads us to 4 maps below
ea2c3f6f554561 Oscar Salvador 2019-03-05 540 * the threshold, otherwise return -ENOMEM here to be more safe.
ea2c3f6f554561 Oscar Salvador 2019-03-05 541 */
ea2c3f6f554561 Oscar Salvador 2019-03-05 542 if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
ea2c3f6f554561 Oscar Salvador 2019-03-05 543 return -ENOMEM;
ea2c3f6f554561 Oscar Salvador 2019-03-05 544
b22823719302e8 Mike Rapoport 2017-08-02 545 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
ecc1a8993751de Al Viro 2009-11-24 546 if (ret)
ecc1a8993751de Al Viro 2009-11-24 547 goto out;
ecc1a8993751de Al Viro 2009-11-24 548
ecc1a8993751de Al Viro 2009-11-24 549 if (old_len >= new_len) {
897ab3e0c49e24 Mike Rapoport 2017-02-24 550 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
ecc1a8993751de Al Viro 2009-11-24 551 if (ret && old_len != new_len)
ecc1a8993751de Al Viro 2009-11-24 552 goto out;
ecc1a8993751de Al Viro 2009-11-24 553 old_len = new_len;
ecc1a8993751de Al Viro 2009-11-24 554 }
ecc1a8993751de Al Viro 2009-11-24 555
98663ca0550162 Brian Geffon 2020-01-22 556 /*
98663ca0550162 Brian Geffon 2020-01-22 557 * MREMAP_DONTUNMAP expands by old_len + (new_len - old_len), we will
98663ca0550162 Brian Geffon 2020-01-22 558 * check that we can expand by old_len and vma_to_resize will handle
98663ca0550162 Brian Geffon 2020-01-22 559 * the vma growing.
98663ca0550162 Brian Geffon 2020-01-22 560 */
98663ca0550162 Brian Geffon 2020-01-22 @561 if (unlikely(flags & MREMAP_DONTUNMAP && !may_expand_vm(mm,
98663ca0550162 Brian Geffon 2020-01-22 562 vma->vm_flags, old_len >> PAGE_SHIFT))) {
^^^^^^^^^^^^^

98663ca0550162 Brian Geffon 2020-01-22 563 ret = -ENOMEM;
98663ca0550162 Brian Geffon 2020-01-22 564 goto out;
98663ca0550162 Brian Geffon 2020-01-22 565 }
98663ca0550162 Brian Geffon 2020-01-22 566
ecc1a8993751de Al Viro 2009-11-24 567 vma = vma_to_resize(addr, old_len, new_len, &charged);
^^^^^^^^^^^^^^^^^^^^

ecc1a8993751de Al Viro 2009-11-24 568 if (IS_ERR(vma)) {
ecc1a8993751de Al Viro 2009-11-24 569 ret = PTR_ERR(vma);
ecc1a8993751de Al Viro 2009-11-24 570 goto out;
ecc1a8993751de Al Viro 2009-11-24 571 }
ecc1a8993751de Al Viro 2009-11-24 572
097eed103862f9 Al Viro 2009-11-24 573 map_flags = MAP_FIXED;

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation

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