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[67.164.59.41]) by smtp.googlemail.com with ESMTPSA id d2e1a72fcca58-71944a9cab5sm1294742b3a.5.2024.09.14.12.43.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Sep 2024 12:43:47 -0700 (PDT) From: "Vishal Moola (Oracle)" To: Muchun Song , syzbot , Andrew Morton , LKML , Linux Memory Management List , syzkaller-bugs@googlegroups.com Cc: "Vishal Moola (Oracle)" , stable@vger.kernel.org Subject: [PATCH 2/2] mm/hugetlb.c: Fix UAF of vma in hugetlb fault pathway Date: Sat, 14 Sep 2024 12:41:19 -0700 Message-ID: <20240914194243.245-2-vishal.moola@gmail.com> X-Mailer: git-send-email 2.45.0 In-Reply-To: <20240914194243.245-1-vishal.moola@gmail.com> References: <7B2E5B76-8FC6-49EA-B0B3-2452ED6ABC5D@linux.dev> <20240914194243.245-1-vishal.moola@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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(). Reported-by: syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@google.com/ Fixes: 9acad7ba3e25 ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()") Signed-off-by: Vishal Moola (Oracle) Cc: --- mm/hugetlb.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 5c77defad295..190fa05635f4 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5915,7 +5915,7 @@ static vm_fault_t hugetlb_wp(struct folio *pagecache_folio, * 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; @@ -6114,7 +6114,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping, } if (!(vma->vm_flags & VM_MAYSHARE)) { - ret = vmf_anon_prepare(vmf); + ret = __vmf_anon_prepare(vmf); if (unlikely(ret)) goto out; } @@ -6245,6 +6245,14 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping, 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; @@ -6466,6 +6474,14 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } 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 -- 2.45.0