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...

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: 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@gmail.com Fixes: 9acad7ba3e25 ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()") Reported-by: syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@google.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 | 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@gmail.com are

mm-change-vmf_anon_prepare-to-__vmf_anon_prepare.patch mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway.patch