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<94b4686a-fee8-c545-2692-b25285b9a152@schaufler-ca.com> <7caa3aa06cc2d7f8d075306b92b259dab3e9bc21.camel@linux.ibm.com> <20230921-gedanken-salzwasser-40d25b921162@brauner> <7ef00ceb49abbb29c49a39287a7c3f28e00cf82a.camel@linux.ibm.com> <028eefb0207e8cb163617ef28b8104e98d00ca2e.camel@kernel.org> <7e211a0e0ccf335143abe8e8b6366bbbfada36f8.camel@linux.ibm.com> In-Reply-To: From: Amir Goldstein Date: Thu, 21 Sep 2023 20:01:51 +0300 Message-ID: Subject: Re: [syzbot] [integrity] [overlayfs] general protection fault in d_path To: Mimi Zohar Cc: Jeff Layton , Christian Brauner , Casey Schaufler , Stefan Berger , syzbot , linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, miklos@szeredi.hu, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org On Thu, Sep 21, 2023 at 7:31=E2=80=AFPM Mimi Zohar wr= ote: > > On Thu, 2023-09-21 at 11:39 -0400, Jeff Layton wrote: > > On Thu, 2023-09-21 at 11:19 -0400, Mimi Zohar wrote: > > > On Thu, 2023-09-21 at 11:10 -0400, Jeff Layton wrote: > > > > On Thu, 2023-09-21 at 10:52 -0400, Mimi Zohar wrote: > > > > > On Thu, 2023-09-21 at 13:48 +0200, Christian Brauner wrote: > > > > > > On Thu, Sep 21, 2023 at 07:24:23AM -0400, Mimi Zohar wrote: > > > > > > > On Thu, 2023-09-21 at 06:32 -0400, Jeff Layton wrote: > > > > > > > > On Wed, 2023-09-20 at 17:52 -0700, Casey Schaufler wrote: > > > > > > > > > On 9/20/2023 5:10 PM, Stefan Berger wrote: > > > > > > > > > > > > > > > > > > > > On 9/20/23 18:09, Stefan Berger wrote: > > > > > > > > > > > > > > > > > > > > > > On 9/20/23 17:16, Jeff Layton wrote: > > > > > > > > > > > > On Wed, 2023-09-20 at 16:37 -0400, Stefan Berger wr= ote: > > > > > > > > > > > > > On 9/20/23 13:01, Stefan Berger wrote: > > > > > > > > > > > > > > On 9/17/23 20:04, syzbot wrote: > > > > > > > > > > > > > > > syzbot has bisected this issue to: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > commit db1d1e8b9867aae5c3e61ad7859abfcc4a6fd6= c7 > > > > > > > > > > > > > > > Author: Jeff Layton > > > > > > > > > > > > > > > Date: Mon Apr 17 16:55:51 2023 +0000 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > IMA: use vfs_getattr_nosec to get the i= _version > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > bisection log: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/bisect.txt?x= =3D106f7e54680000 > > > > > > > > > > > > > > > start commit: a747acc0b752 Merge tag > > > > > > > > > > > > > > > 'linux-kselftest-next-6.6-rc2' > > > > > > > > > > > > > > > of g.. > > > > > > > > > > > > > > > git tree: upstream > > > > > > > > > > > > > > > final oops: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/report.txt?x= =3D126f7e54680000 > > > > > > > > > > > > > > > console output: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/log.txt?x=3D1= 46f7e54680000 > > > > > > > > > > > > > > > kernel config: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/.config?x=3Dd= f91a3034fe3f122 > > > > > > > > > > > > > > > dashboard link: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/bug?extid=3Da67= fc5321ffb4b311c98 > > > > > > > > > > > > > > > syz repro: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/repro.syz?x= =3D1671b694680000 > > > > > > > > > > > > > > > C reproducer: > > > > > > > > > > > > > > > https://syzkaller.appspot.com/x/repro.c?x=3D1= 4ec94d8680000 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Reported-by: syzbot+a67fc5321ffb4b311c98@syzk= aller.appspotmail.com > > > > > > > > > > > > > > > Fixes: db1d1e8b9867 ("IMA: use vfs_getattr_no= sec to get the > > > > > > > > > > > > > > > i_version") > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > For information about bisection process see: > > > > > > > > > > > > > > > https://goo.gl/tpsmEJ#bisection > > > > > > > > > > > > > > The final oops shows this here: > > > > > > > > > > > > > > > > > > > > > > > > > > > > BUG: kernel NULL pointer dereference, address: = 0000000000000058 > > > > > > > > > > > > > > #PF: supervisor read access in kernel mode > > > > > > > > > > > > > > #PF: error_code(0x0000) - not-present page > > > > > > > > > > > > > > PGD 0 P4D 0 > > > > > > > > > > > > > > Oops: 0000 [#1] PREEMPT SMP > > > > > > > > > > > > > > CPU: 0 PID: 3192 Comm: syz-executor.0 Not taint= ed > > > > > > > > > > > > > > 6.4.0-rc2-syzkaller #0 > > > > > > > > > > > > > > Hardware name: Google Google Compute Engine/Goo= gle Compute Engine, > > > > > > > > > > > > > > BIOS Google 08/04/2023 > > > > > > > > > > > > > > RIP: 0010:__lock_acquire+0x35/0x490 kernel/lock= ing/lockdep.c:4946 > > > > > > > > > > > > > > Code: 83 ec 18 65 4c 8b 35 aa 60 f4 7e 83 3d b7= 11 e4 02 00 0f 84 05 > > > > > > > > > > > > > > 02 00 00 4c 89 cb 89 cd 41 89 d5 49 89 ff 83 fe= 01 77 0c 89 f0 > > > > > > > > > > > > > > <49> 8b > > > > > > > > > > > > > > 44 c7 08 48 85 c0 75 1b 4c 89 ff 31 d2 45 89 c4= e8 74 f6 ff > > > > > > > > > > > > > > RSP: 0018:ffffc90002edb840 EFLAGS: 00010097 > > > > > > > > > > > > > > RAX: 0000000000000000 RBX: 0000000000000000 RCX= : 0000000000000002 > > > > > > > > > > > > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI= : 0000000000000050 > > > > > > > > > > > > > > RBP: 0000000000000002 R08: 0000000000000001 R09= : 0000000000000000 > > > > > > > > > > > > > > R10: 0000000000000000 R11: 0000000000000000 R12= : 0000000000000000 > > > > > > > > > > > > > > R13: 0000000000000000 R14: ffff888102ea5340 R15= : 0000000000000050 > > > > > > > > > > > > > > FS: 0000000000000000(0000) GS:ffff88813bc00000= (0000) > > > > > > > > > > > > > > knlGS:0000000000000000 > > > > > > > > > > > > > > CS: 0010 DS: 0000 ES: 0000 CR0: 00000000800500= 33 > > > > > > > > > > > > > > CR2: 0000000000000058 CR3: 0000000003aa8000 CR4= : 00000000003506f0 > > > > > > > > > > > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2= : 0000000000000000 > > > > > > > > > > > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7= : 0000000000000400 > > > > > > > > > > > > > > Call Trace: > > > > > > > > > > > > > > > > > > > > > > > > > > > > lock_acquire+0xd8/0x1f0 kernel/locking/lockde= p.c:5691 > > > > > > > > > > > > > > seqcount_lockdep_reader_access include/linux/= seqlock.h:102 [inline] > > > > > > > > > > > > > > get_fs_root_rcu fs/d_path.c:243 [inline] > > > > > > > > > > > > > > d_path+0xd1/0x1f0 fs/d_path.c:285 > > > > > > > > > > > > > > audit_log_d_path+0x65/0x130 kernel/audit.c:21= 39 > > > > > > > > > > > > > > dump_common_audit_data security/lsm_audit.c:2= 24 [inline] > > > > > > > > > > > > > > common_lsm_audit+0x3b3/0x840 security/lsm_aud= it.c:458 > > > > > > > > > > > > > > smack_log+0xad/0x130 security/smack/smack_acc= ess.c:383 > > > > > > > > > > > > > > smk_tskacc+0xb1/0xd0 security/smack/smack_acc= ess.c:253 > > > > > > > > > > > > > > smack_inode_getattr+0x8a/0xb0 security/smack/= smack_lsm.c:1187 > > > > > > > > > > > > > > security_inode_getattr+0x32/0x50 security/sec= urity.c:2114 > > > > > > > > > > > > > > vfs_getattr+0x1b/0x40 fs/stat.c:167 > > > > > > > > > > > > > > ovl_getattr+0xa6/0x3e0 fs/overlayfs/inode.c:1= 73 > > > > > > > > > > > > > > ima_check_last_writer security/integrity/ima/= ima_main.c:171 > > > > > > > > > > > > > > [inline] > > > > > > > > > > > > > > ima_file_free+0xbd/0x130 security/integrity/i= ma/ima_main.c:203 > > > > > > > > > > > > > > __fput+0xc7/0x220 fs/file_table.c:315 > > > > > > > > > > > > > > task_work_run+0x7d/0xa0 kernel/task_work.c:17= 9 > > > > > > > > > > > > > > exit_task_work include/linux/task_work.h:38 [= inline] > > > > > > > > > > > > > > do_exit+0x2c7/0xa80 kernel/exit.c:871 <------= ----------------- > > > > > > > > > > > > > > do_group_exit+0x85/0xa0 kernel/exit.c:1021 > > > > > > > > > > > > > > get_signal+0x73c/0x7f0 kernel/signal.c:2874 > > > > > > > > > > > > > > arch_do_signal_or_restart+0x89/0x290 arch/x86= /kernel/signal.c:306 > > > > > > > > > > > > > > exit_to_user_mode_loop+0x61/0xb0 kernel/entry= /common.c:168 > > > > > > > > > > > > > > exit_to_user_mode_prepare+0x64/0xb0 kernel/en= try/common.c:204 > > > > > > > > > > > > > > __syscall_exit_to_user_mode_work kernel/entry= /common.c:286 [inline] > > > > > > > > > > > > > > syscall_exit_to_user_mode+0x2b/0x1d0 kernel/e= ntry/common.c:297 > > > > > > > > > > > > > > do_syscall_64+0x4d/0x90 arch/x86/entry/common= .c:86 > > > > > > > > > > > > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > do_exit has called exit_fs(tsk) [ > > > > > > > > > > > > > > https://elixir.bootlin.com/linux/v6.4-rc2/sourc= e/kernel/exit.c#L867 ] > > > > > > > > > > > > > > > > > > > > > > > > > > > > exit_fs(tsk) has set tsk->fs =3D NULL [ > > > > > > > > > > > > > > https://elixir.bootlin.com/linux/v6.4-rc2/sourc= e/fs/fs_struct.c#L103 > > > > > > > > > > > > > > ] > > > > > > > > > > > > > > > > > > > > > > > > > > > > I think this then bites in d_path() where it ca= lls: > > > > > > > > > > > > > > > > > > > > > > > > > > > > get_fs_root_rcu(current->fs, &root); [ > > > > > > > > > > > > > > https://elixir.bootlin.com/linux/v6.4-rc2/sourc= e/fs/d_path.c#L285 ] > > > > > > > > > > > > > > > > > > > > > > > > > > > > current->fs is likely NULL here. > > > > > > > > > > > > > > > > > > > > > > > > > > > > If this was correct it would have nothing to do= with the actual > > > > > > > > > > > > > > patch, > > > > > > > > > > > > > > though, but rather with the fact that smack log= s on process > > > > > > > > > > > > > > termination. I am not sure what the solution wo= uld be other than > > > > > > > > > > > > > > testing for current->fs =3D=3D NULL in d_path b= efore using it and > > > > > > > > > > > > > > returning an error that is not normally returne= d or trying to > > > > > > > > > > > > > > intercept this case in smack. > > > > > > > > > > > > > I have now been able to recreate the syzbot issue= with the test > > > > > > > > > > > > > program > > > > > > > > > > > > > and the issue is exactly the one described here, = current->fs =3D=3D NULL. > > > > > > > > > > > > > > > > > > > > > > > > > Earlier in this thread, Amir had a diagnosis that I= MA is > > > > > > > > > > > > inappropriately > > > > > > > > > > > > trying to use f_path directly instead of using the = helpers that are > > > > > > > > > > > > friendly for stacking filesystems. > > > > > > > > > > > > > > > > > > > > > > > > https://lore.kernel.org/linux-fsdevel/CAOQ4uxgjnYye= QL-LbS5kQ7+C0d6sjzKqMDWAtZW8cAkPaed6=3DQ@mail.gmail.com/ > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'm not an IMA hacker so I'm not planning to roll a= fix here. Perhaps > > > > > > > > > > > > someone on the IMA team could try this approach? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I have applied this patch here from Amir now and it d= oes NOT resolve > > > > > > > > > > > the issue: > > > > > > > > > > > > > > > > > > > > > > https://lore.kernel.org/linux-integrity/296dae962a2a4= 88bde682d3def074db91686e1c3.camel@linux.ibm.com/T/#m4ebdb780bf6952e7f210c55= e87950d0cfa1d5eb0 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > This seems to resolve the issue: > > > > > > > > > > > > > > > > > > > > diff --git a/security/smack/smack_access.c > > > > > > > > > > b/security/smack/smack_access.c > > > > > > > > > > index 585e5e35710b..57afcea1e39b 100644 > > > > > > > > > > --- a/security/smack/smack_access.c > > > > > > > > > > +++ b/security/smack/smack_access.c > > > > > > > > > > @@ -347,6 +347,9 @@ void smack_log(char *subject_label,= char > > > > > > > > > > *object_label, int request, > > > > > > > > > > struct smack_audit_data *sad; > > > > > > > > > > struct common_audit_data *a =3D &ad->a; > > > > > > > > > > > > > > > > > > > > + if (current->flags & PF_EXITING) > > > > > > > > > > + return; > > > > > > > > > > + > > > > > > > > > > > > > > > > > > Based on what I see here I can understand that this preve= nts the panic, > > > > > > > > > but it isn't so clear what changed that introduced the pr= oblem. > > > > > > > > > > > > > > > > > > > /* check if we have to log the current event */ > > > > > > > > > > if (result < 0 && (log_policy & SMACK_AUDIT_DEN= IED) =3D=3D 0) > > > > > > > > > > return; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Apparently, it's this patch: > > > > > > > > > > > > > > > > db1d1e8b9867 IMA: use vfs_getattr_nosec to get the i_ve= rsion > > > > > > > > > > > > > > Yes, the syzbot was updated with that info. > > > > > > > > > > > > > > > At one time, IMA would reach directly into the inode to get= the > > > > > > > > i_version and ctime. That was fine for certain filesystems,= but with > > > > > > > > more recent changes it needs to go through ->getattr instea= d. Evidently, > > > > > > > > it's selecting the wrong inode to query when dealing with o= verlayfs and > > > > > > > > that's causing panics at times. > > > > > > > > > > > > > > > > As to why the above patch helps, I'm not sure, but given th= at it doesn't > > > > > > > > seem to change which inode is being queried via getattr, it= seems like > > > > > > > > this is probably papering over the real bug. That said, IMA= and > > > > > > > > overlayfs are not really in my wheelhouse, so I could be ve= ry wrong > > > > > > > > here. > > > > > > > > > > > > > > The call to vfs_getattr_nosec() somehow triggers a call to > > > > > > > security_inode_getattr(). Without the call neither ovl_getat= tr() nor > > > > > > > smack_inode_getattr() would be called. > > > > > > > > > > > > ima_file_free() > > > > > > -> ima_check_last_writer() > > > > > > -> vfs_getattr_nosec() > > > > > > -> i_op->getattr() =3D=3D ovl_getattr() > > > > > > -> vfs_getattr() > > > > > > -> security_inode_getattr() > > > > > > -> real_i_op->getattr() > > > > > > > > > > > > is the callchain that triggers this. > > > > > > > > > > Thank you for the explanation as to why ovl_getattr() and subsequ= ently > > > > > smack_inode_getattr() is being called. > > > > > > > > > > > > > > > > > ima_file_free() is called in a very sensitive location: __fput(= ) that > > > > > > can be called from task work when the process is already PF_EXI= TING. > > > > > > > > > > > > The ideal solution would be for ima to stop calling back into t= he > > > > > > filesystems in this location at all but that's probably not goi= ng to > > > > > > happen because I now realize you also set extended attributes f= rom > > > > > > __fput(): > > > > > > > > > > > > > > > > > > ima_check_last_writer() > > > > > > -> ima_update_xatt() > > > > > > -> ima_fix_xattr() > > > > > > -> __vfs_setxattr_noperm() > > > > > > > > > > > > The __vfs_setxattr_noperm() codepath can itself trigger > > > > > > security_inode_post_setxattr() and security_inode_setsecurity()= . So > > > > > > those hooks are hopefully safe to be called with PF_EXITING tas= ks as > > > > > > well... > > > > > > > > > > > > Imho, this is all very wild but I'm not judging. > > > > > > > > > > Measuring and verifying immutable files is straight forward. > > > > > Measuring, verifiying, and updating mutable file hashes is a lot = more > > > > > complicated. Re-calculating the file hash everytime the file cha= nges > > > > > would impact performance. The file hash is currently updated as = the > > > > > last writer closes the file (__fput). One of the reasons for the= wq > > > > > was for IMA to safely calculate the file hash and and take the i_= mutex > > > > > to write the xattr. > > > > > > > > > > IMA support for mutable files makes IMA a lot more complicated. = Any > > > > > improvement suggestions would be appreciated. > > > > > > > > > > > > > > > > > Two solutions imho: > > > > > > (1) teach stacking filesystems like overlayfs and ecryptfs to u= se > > > > > > vfs_getattr_nosec() in their ->getattr() implementation whe= n they > > > > > > are themselves called via vfs_getattr_nosec(). This will fi= x this by > > > > > > not triggering another LSM hook. > > > > > > (2) make all ->getattr() LSM hooks PF_EXITING safe ideally don'= t do > > > > > > anything > > > > > > > > > > The original problem was detecting i_version change on overlayfs. > > > > > > > > > > Amir's proposed patch might resolve it without commit db1d1e8b986= 7 > > > > > ("IMA: use vfs_getattr_nosec to get the i_version"). However, as= Amir > > > > > said, it does not address the new problem introduced by it. Ass= uming > > > > > Amir's proposed patch resolves the original problem, an alternati= ve > > > > > solution would be to revert commit db1d1e8b9867. > > > > > > > > > > > > > If you're going to revert that commit, then I'm wondering what you > > > > intend to do instead. Reaching directly into the inode to get this > > > > information is really no bueno. > > > > > > IMA detecting file change based on i_version has been there since IMA > > > was upstreamed. Please explain why this is not a good idea. > > > > > > > Not all i_version values are managed in the same way. Network > > filesystems need to pass through the value from the server, whereas wit= h > > a local filesystems the kernel needs to manage the increment. > > > > IMA is mostly interested in local filesystems at the moment. The main > > kernel-managed versions in the kernel are in btrfs, ext4 and xfs and > > tmpfs. Until recently, only btrfs had one that functioned properly. Bot= h > > ext4 and xfs would also increment their values on atime updates. In > > practical terms, this means that IMA ends up doing unnecessary > > remeasurements after read events in some cases. > > > > ext4 recently had its i_version value fixed to not do this, but the XFS > > developers are unable to fix theirs to avoid incrementing on atime > > updates. For that, I'm working on the multigrain ctime patches which > > should allow XFS to fake up a STATX_CHANGE_COOKIE in its getattr > > routine. > > > > IMA has no practical way to tell what the filesystem can do if it's > > groveling around inside struct inode, which is why I recommended using > > vfs_getattr_nosec to grab this info. If that's problematic then by all > > means, back out that patch, but you'll need to come up with some way to > > deal with the different nuances of the different i_version counters in > > across different filesystems. > > Got it. This is basically a performance issue, because i_version is > being updated too frequently on some filesystems. It's not an issue of > missing measurements or not re-evaluting the file's integrity when > needed. > > Let's see if Amir's patch actually fixes the original problem before > making any decisions. (Wishing for a reproducer of the original > problem.) > Confused. What is the "original problem"? I never claimed that my patch fixes the "original problem". I claimed [1] that my patch fixes a problem that existed before db1d1e8b9867, but db1d1e8b9867 added two more instances of that bug (wrong dereference of file->f_path). Apparently, db1d1e8b9867 introduced another bug. It looks like you should revert db1d1e8b9867, but regardless, I recommend that you apply my patch. My patch conflicts with the revert but the conflict is trivial - the two hunks that fix the new vfs_getattr_nosec() calls are irrelevant - the rest are. Thanks, Amir. [1] https://lore.kernel.org/linux-unionfs/20230913073755.3489676-1-amir73il= @gmail.com/