Commit 37641efa authored Apr 15, 2024 by Vishal Moola (Oracle) Committed by Andrew Morton Apr 24, 2024

hugetlb: check for anon_vma prior to folio allocation

Commit 9acad7ba ("hugetlb: use vmf_anon_prepare() instead of
anon_vma_prepare()") may bailout after allocating a folio if we do not
hold the mmap lock.  When this occurs, vmf_anon_prepare() will release the
vma lock.  Hugetlb then attempts to call restore_reserve_on_error(), which
depends on the vma lock being held.

We can move vmf_anon_prepare() prior to the folio allocation in order to
avoid calling restore_reserve_on_error() without the vma lock.

Link: https://lkml.kernel.org/r/ZiFqSrSRLhIV91og@fedora


Fixes: 9acad7ba ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()")
Reported-by:  <syzbot+ad1b592fc4483655438b@syzkaller.appspotmail.com>
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 682886ec

mm/hugetlb.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -6261,6 +6261,12 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
		VM_UFFD_MISSING);
		}

		if (!(vma->vm_flags & VM_MAYSHARE)) {
		ret = vmf_anon_prepare(vmf);
		if (unlikely(ret))
		goto out;
		}

		folio = alloc_hugetlb_folio(vma, haddr, 0);
		if (IS_ERR(folio)) {
		/*
		@@ -6297,15 +6303,12 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
		*/
		restore_reserve_on_error(h, vma, haddr, folio);
		folio_put(folio);
		ret = VM_FAULT_SIGBUS;
		goto out;
		}
		new_pagecache_folio = true;
		} else {
		folio_lock(folio);

		ret = vmf_anon_prepare(vmf);
		if (unlikely(ret))
		goto backout_unlocked;
		anon_rmap = 1;
		}
		} else {