From: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx> commit 98b74bb4d7e96b4da5ef3126511febe55b76b807 upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6076,7 +6076,7 @@ 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; @@ -6275,7 +6275,7 @@ 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; } @@ -6406,6 +6406,14 @@ 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; @@ -6627,6 +6635,14 @@ 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 stable-queue which might be from vishal.moola@xxxxxxxxx are queue-6.11/mm-change-vmf_anon_prepare-to-__vmf_anon_prepare.patch queue-6.11/mm-hugetlb.c-fix-uaf-of-vma-in-hugetlb-fault-pathway.patch
