The patch titled
Subject: mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway.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@xxxxxxxxx>
Subject: mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway
Date: Sat, 14 Sep 2024 12:41:19 -0700
Syzbot reports a UAF in hugetlb_fault(). This happens because
vmf_anon_prepare() could drop the per-VMA lock and allow the current VMA
to be freed before hugetlb_vma_unlock_read() is called.
We can fix this by using a modified version of vmf_anon_prepare() that
doesn't release the VMA lock on failure, and then release it ourselves
after hugetlb_vma_unlock_read().
Link: https://lkml.kernel.org/r/20240914194243.245-2-vishal.moola@xxxxxxxxx
Fixes: 9acad7ba3e25 ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()")
Reported-by: syzbot+2dab93857ee95f2eeb08@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@xxxxxxxxxx/
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway
+++ a/mm/hugetlb.c
@@ -6065,7 +6065,7 @@ retry_avoidcopy:
* When the original hugepage is shared one, it does not have
* anon_vma prepared.
*/
- ret = vmf_anon_prepare(vmf);
+ ret = __vmf_anon_prepare(vmf);
if (unlikely(ret))
goto out_release_all;
@@ -6264,7 +6264,7 @@ static vm_fault_t hugetlb_no_page(struct
}
if (!(vma->vm_flags & VM_MAYSHARE)) {
- ret = vmf_anon_prepare(vmf);
+ ret = __vmf_anon_prepare(vmf);
if (unlikely(ret))
goto out;
}
@@ -6395,6 +6395,14 @@ static vm_fault_t hugetlb_no_page(struct
folio_unlock(folio);
out:
hugetlb_vma_unlock_read(vma);
+
+ /*
+ * We must check to release the per-VMA lock. __vmf_anon_prepare() is
+ * the only way ret can be set to VM_FAULT_RETRY.
+ */
+ if (unlikely(ret & VM_FAULT_RETRY))
+ vma_end_read(vma);
+
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
return ret;
@@ -6616,6 +6624,14 @@ out_ptl:
}
out_mutex:
hugetlb_vma_unlock_read(vma);
+
+ /*
+ * We must check to release the per-VMA lock. __vmf_anon_prepare() in
+ * hugetlb_wp() is the only way ret can be set to VM_FAULT_RETRY.
+ */
+ if (unlikely(ret & VM_FAULT_RETRY))
+ vma_end_read(vma);
+
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
/*
* Generally it's safe to hold refcount during waiting page lock. But
_
Patches currently in -mm which might be from vishal.moola@xxxxxxxxx are
mm-change-vmf_anon_prepare-to-__vmf_anon_prepare.patch
mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway.patch
