+ mm-hugetlbc-fix-uaf-of-vma-in-hugetlb-fault-pathway.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@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