+ hugetlb-check-for-anon_vma-prior-to-folio-allocation.patch added to mm-hotfixes-unstable branch

+ hugetlb-check-for-anon_vma-prior-to-folio-allocation.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: hugetlb: check for anon_vma prior to folio allocation
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     hugetlb-check-for-anon_vma-prior-to-folio-allocation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlb-check-for-anon_vma-prior-to-folio-allocation.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
Subject: hugetlb: check for anon_vma prior to folio allocation
Date: Mon, 15 Apr 2024 14:17:47 -0700

Commit 9acad7ba3e25 ("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: 9acad7ba3e25 ("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>
---

 mm/hugetlb.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/mm/hugetlb.c~hugetlb-check-for-anon_vma-prior-to-folio-allocation
+++ a/mm/hugetlb.c
@@ -6261,6 +6261,12 @@ static vm_fault_t hugetlb_no_page(struct
 							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
 				 */
 				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 {
_

Patches currently in -mm which might be from vishal.moola@gmail.com are

hugetlb-check-for-anon_vma-prior-to-folio-allocation.patch
hugetlb-convert-hugetlb_fault-to-use-struct-vm_fault.patch
hugetlb-convert-hugetlb_no_page-to-use-struct-vm_fault.patch
hugetlb-convert-hugetlb_no_page-to-use-struct-vm_fault-fix.patch
hugetlb-convert-hugetlb_wp-to-use-struct-vm_fault.patch
hugetlb-convert-hugetlb_wp-to-use-struct-vm_fault-fix.patch