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+0800 (CST) Received: from [127.0.0.1] (unknown [10.204.63.22]) by APP2 (Coremail) with SMTP id GxC2BwA3mMgQrgZnDq6LAg--.65260S2; Wed, 09 Oct 2024 17:23:54 +0100 (CET) Message-ID: <1a1d106ea8bba8abc1d3f3cd6fdd71d03edcf764.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: Wed, 09 Oct 2024 18:23:40 +0200 In-Reply-To: References: <66f7b10e.050a0220.46d20.0036.GAE@google.com> <05e893036fa8753e0177db99dd48eb9d2e33476a.camel@huaweicloud.com> <70f55efdba0e682907c895ea8ba537ea435bc3aa.camel@huaweicloud.com> 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5gryDn6k2xyIZT7bY87aLBCFTpylwJZfZnCsl6hHrBcxN6y8EwVTawtxFxiyQjUC4MfKpzS6zSclC/XOe/msFcrUOT2AtI2UqRxR14hadFp23DA9RCCwk2t7eOIB7UR725vPNkfKYVeMgifGYXOe74m1fE+mY4V6l4DEKu/TKPzgPI52GbSds3VW/jlpeNXoyqP1mbAHKHZz2ZKuOnQJlic9xNbfjv5I9vl7P8lqrvGv+HATxEss4MZWaDGVsWNCwE62HmTzEfDWjGVuB9rtLpD6OUF9wmVeSpvBA8QOtq5bFeGNuxUcxLrgzaS5ZDPLHIHIcpRP5kfFamjOXjsbFH522+zy2tMX7jB4YR1E4oauyz0YwO258wSV4QlwuXt3l6BjA 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 12:58 -0400, Paul Moore wrote: > On Mon, Oct 7, 2024 at 12:49=E2=80=AFPM Roberto Sassu > wrote: > > 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}, a= t: inode_lock include/linux/fs.h:815 [inline] > > > > > > > ffff888072852370 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, a= t: process_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= _lock_killable include/linux/mmap_lock.h:122 [inline] > > > > > > > ffff88807ac9a798 (&mm->mmap_lock){++++}-{3:3}, at: __do_sys_r= emap_file_pages mm/mmap.c:1649 [inline] > > > > > > > ffff88807ac9a798 (&mm->mmap_lock){++++}-{3:3}, at: __se_sys_r= emap_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 `p= rot` > > > > > > change caused by the processing logic for READ_IMPLIES_EXEC in = do_mmap(), > > > > > > 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 po= sitive. > > > > >=20 > > > > > > The LSM check is required to know what the `prot` is, but `prot= ` must be > > > > > > obtained after holding the `mmap_write_lock`. > > > > > >=20 > > > > > > If the `mmap_write_lock` is released after getting the `prot` a= nd before > > > > > > 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 LS= M > > > > > 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 c= an > > > > 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. > >=20 > > Welcome. Probably it can go down only until the kernel where IMA and > > EVM are LSMs. >=20 > Yes, we'll need to look at that once we solve this in Linus' tree. #syz test: https://github.com/robertosassu/linux.git ima-remove-inode-lock-= v1