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([240d:1a:c0d:9f00:fc9c:8ee9:e32c:2d9]) by smtp.gmail.com with ESMTPSA id gf7-20020a17090ac7c700b00214247989dfsm39222pjb.13.2022.11.03.07.18.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 07:18:06 -0700 (PDT) From: Shigeru Yoshida To: konishi.ryusuke@gmail.com Cc: linux-nilfs@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Shigeru Yoshida , syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com Subject: [PATCH] nilfs: Avoid use-after-free caused by nilfs->ns_writer Date: Thu, 3 Nov 2022 23:17:59 +0900 Message-Id: <20221103141759.1836312-1-syoshida@redhat.com> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" syzbot reported use-after-free in nilfs_segctor_sync() [1]. The use-after-free occurs with nilfs->ns_writer. The scenario for the issue is as follows: Task1 Task2 Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com ---------------------------------------------------------------------- nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before <-- use-after-free While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This patch fixes the issue by taking nilfs->ns_segctor_sem in nilfs_construct_segment() so that nilfs->ns_segctor_sem cannot be freed while nilfs_segctor_sync() is sleeping. Link: https://syzkaller.appspot.com/bug?id=3D79a4c002e960419ca173d55e863bd0= 9e8112df8b [1] Reported-by: syzbot+f816fa82f8783f7a02bb@syzkaller.appspotmail.com Signed-off-by: Shigeru Yoshida --- fs/nilfs2/segment.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c index b4cebad21b48..d4f10d82664d 100644 --- a/fs/nilfs2/segment.c +++ b/fs/nilfs2/segment.c @@ -2239,16 +2239,24 @@ static void nilfs_segctor_wakeup(struct nilfs_sc_in= fo *sci, int err) int nilfs_construct_segment(struct super_block *sb) { struct the_nilfs *nilfs =3D sb->s_fs_info; - struct nilfs_sc_info *sci =3D nilfs->ns_writer; + struct nilfs_sc_info *sci; struct nilfs_transaction_info *ti; + int ret; =20 - if (!sci) + down_write(&nilfs->ns_segctor_sem); + sci =3D nilfs->ns_writer; + if (!sci) { + up_write(&nilfs->ns_segctor_sem); return -EROFS; + } =20 /* A call inside transactions causes a deadlock. */ BUG_ON((ti =3D current->journal_info) && ti->ti_magic =3D=3D NILFS_TI_MAG= IC); =20 - return nilfs_segctor_sync(sci); + ret =3D nilfs_segctor_sync(sci); + up_write(&nilfs->ns_segctor_sem); + + return ret; } =20 /** --=20 2.37.3