[PATCH] hugetlb: Check for anon_vma prior to folio allocation

From: Vishal Moola (Oracle)
Date: Mon Apr 15 2024 - 17:17:47 EST


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.

Fixes: 9acad7ba3e25 ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()")
CC: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+ad1b592fc4483655438b@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
---
mm/hugetlb.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 23ef240ba48a..948d197cd88f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6274,6 +6274,12 @@ 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)) {
/*
@@ -6310,15 +6316,12 @@ 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 {
--
2.43.0


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