From: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Date: Sat, 14 Sep 2024 19:41:19 +0000 (-0700)
Subject: mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway
X-Git-Tag: v6.10.13~10
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e897d184a8dd4a4e1f39c8c495598e4d9472776c;p=thirdparty%2Fkernel%2Fstable.git

mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway

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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index be77b409de93f..423d20453b90c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6075,7 +6075,7 @@ 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;
 
@@ -6274,7 +6274,7 @@ 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;
 		}
@@ -6406,6 +6406,14 @@ 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;
 
@@ -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