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+0800 (CST) Received: from [127.0.0.1] (unknown [10.204.63.22]) by APP2 (Coremail) with SMTP id GxC2BwDXOMkOEQRnSZ5qAg--.56494S2; Mon, 07 Oct 2024 17:49:29 +0100 (CET) Message-ID: <70f55efdba0e682907c895ea8ba537ea435bc3aa.camel@huaweicloud.com> Subject: Re: [syzbot] [integrity?] [lsm?] possible deadlock in process_measurement (4) From: Roberto Sassu To: Paul Moore Cc: Shu Han , syzbot , akpm@linux-foundation.org, dmitry.kasatkin@gmail.com, eric.snowberg@oracle.com, hughd@google.com, jmorris@namei.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, roberto.sassu@huawei.com, serge@hallyn.com, stephen.smalley.work@gmail.com, syzkaller-bugs@googlegroups.com, zohar@linux.ibm.com Date: Mon, 07 Oct 2024 18:49:15 +0200 In-Reply-To: References: <66f7b10e.050a0220.46d20.0036.GAE@google.com> <05e893036fa8753e0177db99dd48eb9d2e33476a.camel@huaweicloud.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 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fWc3s992lGwHWzkDEU4UeuHzEcBtc4LinYNreqomCkB44HZu5ybGut5u8879SRgmyPV6A4zUgwagbXhQGAJ5KqkkJDnrT9CnMwJWdyzhGZhiAgu5keSQEdNiGLqAqxshKLaBWVM73l+Glpes1CN3aNBHIK3wpHdW8mpr7x9d1JMsT0q56wYJ2pPjfmsTpRsOBfG/ZQ2Q2ARuqBw9Tr0b0YePrMOulLboii1aonpVS3sQJjWWEJBeSTLPPZZZabthx+WvxLyLgKacx+f+czR6JIvd5V8mVxToR/LUqEGDIOPWO4BJtfXRDxgyWJtXMHYmVtt8pbRNQv9qX7iXJuThsFhaBw4rquKoxAzVwfMa7rxQQfpI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2024-10-07 at 12:35 -0400, Paul Moore wrote: > On Mon, Oct 7, 2024 at 11:31=E2=80=AFAM Roberto Sassu > wrote: > > On Wed, 2024-10-02 at 23:09 -0400, Paul Moore wrote: > > > On Sat, Sep 28, 2024 at 2:08=E2=80=AFPM Shu Han wrote: > > > >=20 > > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D > > > > > WARNING: possible circular locking dependency detected > > > > > 6.11.0-syzkaller-10045-g97d8894b6f4c #0 Not tainted > > > > > ------------------------------------------------------ > > > > > syz-executor369/5231 is trying to acquire lock: > > > > > ffff888072852370 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: i= node_lock include/linux/fs.h:815 [inline] > > > > > ffff888072852370 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: p= rocess_measurement+0x439/0x1fb0 security/integrity/ima/ima_main.c:250 > > > > >=20 > > > > > but task is already holding lock: > > > > > ffff88807ac9a798 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_loc= k_killable include/linux/mmap_lock.h:122 [inline] > > > > > ffff88807ac9a798 (&mm->mmap_lock){++++}-{3:3}, at: __do_sys_remap= _file_pages mm/mmap.c:1649 [inline] > > > > > ffff88807ac9a798 (&mm->mmap_lock){++++}-{3:3}, at: __se_sys_remap= _file_pages+0x22d/0xa50 mm/mmap.c:1624 > > > > >=20 > > > > > which lock already depends on the new lock. > > > >=20 > > > > This issue (if not a false positive?) is due to the possible `prot` > > > > change caused by the processing logic for READ_IMPLIES_EXEC in do_m= map(), > > > > so the remap_file_pages() must perform LSM check before calling do_= mmap(), > > > > this is what the previous commit want to do. > > >=20 > > > My apologies for the delay on this, I was traveling for a bit and > > > missed this issue while away. > > >=20 > > > Looking quickly at the report, I don't believe this is a false positi= ve. > > >=20 > > > > The LSM check is required to know what the `prot` is, but `prot` mu= st be > > > > obtained after holding the `mmap_write_lock`. > > > >=20 > > > > If the `mmap_write_lock` is released after getting the `prot` and b= efore > > > > the LSM call in remap_file_pages(), it may cause TOCTOU. > > >=20 > > > Looking at the IMA code, specifically the process_measurement() > > > function which is called from the security_mmap_file() LSM hook, I'm > > > not sure why there is the inode_lock() protected region. Mimi? > > > Roberto? My best guess is that locking the inode may have been > > > necessary before we moved the IMA inode state into the inode's LSM > > > security blob, but I'm not certain. > > >=20 > > > Mimi and Roberto, can we safely remove the inode locking in > > > process_measurement()? > >=20 > > I discussed a bit with Mimi. Her concern was the duplicate iint > > structure creation during concurrent file accesses. Now that inode > > integrity metadata have been moved to the inode security blob, we can > > take the iint->mutex out of the ima_iint_cache structure, and store it > > directly in the security blob. In this way, we can remove the inode > > lock. > >=20 > > Will write a patch and see if it passes our tests. >=20 > That's great, thanks Roberto. Assuming all goes well we'll want to > backport this everywhere we merged the remap_file_pages() patch. Welcome. Probably it can go down only until the kernel where IMA and EVM are LSMs. Roberto