linux-kernel - [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after being freed

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Date:   Tue, 15 Feb 2022 12:19:22 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     mhocko@...nel.org, mhocko@...e.com, shy828301@...il.com,
        rientjes@...gle.com, willy@...radead.org, hannes@...xchg.org,
        guro@...com, riel@...riel.com, minchan@...nel.org,
        kirill@...temov.name, aarcange@...hat.com, brauner@...nel.org,
        christian@...uner.io, hch@...radead.org, oleg@...hat.com,
        david@...hat.com, jannh@...gle.com, shakeelb@...gle.com,
        luto@...nel.org, christian.brauner@...ntu.com, fweimer@...hat.com,
        jengelh@...i.de, timmurray@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        surenb@...gle.com,
        syzbot+2ccf63a4bd07cf39cab0@...kaller.appspotmail.com
Subject: [PATCH 1/1] mm: fix use-after-free bug when mm->mmap is reused after
 being freed

After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset,
otherwise it points to a vma that was freed and when reused leads to
a use-after-free bug.

Reported-by: syzbot+2ccf63a4bd07cf39cab0@...kaller.appspotmail.com
Suggested-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 mm/mmap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 1e8fdb0b51ed..d445c1b9d606 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm)
 		vma = remove_vma(vma);
 		cond_resched();
 	}
+	mm->mmap = NULL;
 	mmap_write_unlock(mm);
 	vm_unacct_memory(nr_accounted);
 }
-- 
2.35.1.265.g69c8d7142f-goog