Messages in this thread | | | Subject | Re: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12] | From | Alan Jenkins <> | Date | Wed, 17 Oct 2018 18:45:51 +0100 |
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Hi David. I think there's an outstanding point below, have you been thinking about it?
On 07/10/2018 11:48, Alan Jenkins wrote: > On 05/10/2018 19:24, Alan Jenkins wrote: >> On 21/09/2018 17:30, David Howells wrote: >>> From: Al Viro <viro@zeniv.linux.org.uk> >>> >>> Allow a detached tree created by open_tree(..., OPEN_TREE_CLONE) to be >>> attached by move_mount(2). >>> >>> If by the time of final fput() of OPEN_TREE_CLONE-opened file its >>> tree is >>> not detached anymore, it won't be dissolved. move_mount(2) is adjusted >>> to handle detached source. >>> >>> That gives us equivalents of mount --bind and mount --rbind. >>> >>> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> >>> Signed-off-by: David Howells <dhowells@redhat.com> >>> --- >>> >>> fs/namespace.c | 26 ++++++++++++++++++++------ >>> 1 file changed, 20 insertions(+), 6 deletions(-) >>> >>> diff --git a/fs/namespace.c b/fs/namespace.c >>> index dd38141b1723..caf5c55ef555 100644 >>> --- a/fs/namespace.c >>> +++ b/fs/namespace.c >>> @@ -1785,8 +1785,10 @@ void dissolve_on_fput(struct vfsmount *mnt) >>> { >>> namespace_lock(); >>> lock_mount_hash(); >>> - mntget(mnt); >>> - umount_tree(real_mount(mnt), UMOUNT_CONNECTED); >>> + if (!real_mount(mnt)->mnt_ns) { >>> + mntget(mnt); >>> + umount_tree(real_mount(mnt), UMOUNT_CONNECTED); >>> + } >>> unlock_mount_hash(); >>> namespace_unlock(); >>> } >>> @@ -2393,6 +2395,7 @@ static int do_move_mount(struct path >>> *old_path, struct path *new_path) >>> struct mount *old; >>> struct mountpoint *mp; >>> int err; >>> + bool attached; >>> mp = lock_mount(new_path); >>> err = PTR_ERR(mp); >>> @@ -2403,10 +2406,19 @@ static int do_move_mount(struct path >>> *old_path, struct path *new_path) >>> p = real_mount(new_path->mnt); >>> err = -EINVAL; >>> - if (!check_mnt(p) || !check_mnt(old)) >>> + /* The mountpoint must be in our namespace. */ >>> + if (!check_mnt(p)) >>> + goto out1; >>> + /* The thing moved should be either ours or completely >>> unattached. */ >>> + if (old->mnt_ns && !check_mnt(old)) >>> goto out1; >>> - if (!mnt_has_parent(old)) >>> + attached = mnt_has_parent(old); >>> + /* >>> + * We need to allow open_tree(OPEN_TREE_CLONE) followed by >>> + * move_mount(), but mustn't allow "/" to be moved. >>> + */ >>> + if (old->mnt_ns && !attached) >>> goto out1; >>> if (old->mnt.mnt_flags & MNT_LOCKED) >> >> Hi >> >> I replied last time to wonder about the MNT_UMOUNT mnt_flag. So I've >> tested it now :-), on David's current tree (commit 5581f4935add). >> >> The modified do_move_mount() allows re-attaching something that was >> lazy-unmounted. But the lazy unmount sets MNT_UMOUNT. And this flag >> is not cleared when the mount is re-attached. >> >> I wasn't sure what effect this would have. Luckily it showed up >> straight away, when I tried to unmount again. It causes a soft lockup. >> >> Debug printk: >> >> diff --git a/fs/namespace.c b/fs/namespace.c >> index 4dfe7e23b7ee..ac8de9191cfe 100644 >> --- a/fs/namespace.c >> +++ b/fs/namespace.c >> @@ -2472,6 +2472,10 @@ static int do_move_mount(struct path >> *old_path, struct path *new_path) >> if (old->mnt.mnt_flags & MNT_LOCKED) >> goto out1; >> >> + pr_info("mnt_flags=%x umount=%x\n", >> + (unsigned) old->mnt.mnt_flags, >> + (unsigned) !!(old->mnt.mnt_flags & MNT_UMOUNT); >> + >> if (old_path->dentry != old_path->mnt->mnt_root) >> goto out1; > > The lockup seems to be a general problem with the cleanup code. Even > if I use this as advertised, i.e. for a simple bind mount. > > (I was suspicious that being able to pass around detached trees as an > FD, and re-attach them in any namespace, allows leaking memory by > creating a namespace loop. I.e. maybe it gives you enough rope to > skip the test in mnt_ns_loop(). But I didn't get that far). > > I converted test-fsmount.c for my own purposes: > > diff --git a/samples/vfs/test-fsmount.c b/samples/vfs/test-fsmount.c > index 74124025ade0..da6e3fbf0513 100644 > --- a/samples/vfs/test-fsmount.c > +++ b/samples/vfs/test-fsmount.c > @@ -83,6 +83,11 @@ static inline int move_mount(int from_dfd, const > char *from_pathname, > to_dfd, to_pathname, flags); > } > > +static inline int open_tree(int dfd, const char *pathname, unsigned > flags) > +{ > + return syscall(__NR_open_tree, dfd, pathname, flags); > +} > + > #define E_fsconfig(fd, cmd, key, val, aux) \ > do { \ > if (fsconfig(fd, cmd, key, val, aux) == -1) \ > @@ -93,6 +98,7 @@ int main(int argc, char *argv[]) > { > int fsfd, mfd; > > +#if 0 > /* Mount a publically available AFS filesystem */ > fsfd = fsopen("afs", 0); > if (fsfd == -1) { > @@ -115,4 +121,9 @@ int main(int argc, char *argv[]) > > E(close(mfd)); > exit(0); > +#endif > + > + E( mfd = open_tree(-1, "/mnt", OPEN_TREE_CLONE) ); > + E( fchdir(mfd) ); > + E( execl("/bin/bash", "/bin/bash", NULL) ); > } > > If I close() the mount FD "mfd", and then do "mount --move . /mnt", my > printk() shows MNT_UMOUNT has been set. ( I guess fchdir() works more > like openat(... , O_PATH) than dup() ). Then unmounting /mnt hangs, as > I would expect from my previous test.
^ You posted a diff that would solve this problem
> > > If I instead do the mount+unmount first, and close the FD as a second > step, I think there's a lockup in the close(). The lockup happens in > the same place as the unmount lockup from before.
^ but I don't think you have addressed this problem in your replies so far.
Thanks
Alan
> (Except there's a line "Code: Bad RIP value", I don't know why that > happens). > > # unshare --mount > # test-fsmount > # mount --move . /mnt > [ 270.859542] umount=0 mnt_flags=20 > > Check the flags are still the same: > > # mount --move /mnt /mnt > [ 305./mnt: mount(2) system call failed: Too many levels of symbolic > links. > [ 313.737030] umount=0 mnt_flags=20 > > Clean up the bind mount, and then the inherited mount FD. > > # cd > # umount /mnt > # exit > > [ 351.898629] watchdog: BUG: soft lockup - CPU#0 stuck for 22s! > [bash:1483] > [ 351.899841] Modules linked in: xt_CHECKSUM(E) ipt_MASQUERADE(E) > tun(E) bridge(E) stp(E) llc(E) ip6t_rpfilter(E) ip6t_REJECT(E) > nf_reject_ipv6(E) xt_conntrack(E) ip6table_nat(E) nf_nat_ipv6(E) > devlink(E) ip6table_mangle(E) ip6table_raw(E) ip6table_security(E) > iptable_nat(E) nf_nat_ipv4(E) nf_nat(E) nf_conntrack(E) > nf_defrag_ipv6(E) libcrc32c(E) nf_defrag_ipv4(E) iptable_mangle(E) > iptable_raw(E) iptable_security(E) ip6table_filter(E) ip6_tables(E) > snd_hda_codec_generic(E) snd_hda_intel(E) snd_hda_codec(E) > snd_hwdep(E) snd_hda_core(E) snd_seq(E) snd_seq_device(E) snd_pcm(E) > joydev(E) crc32_pclmul(E) snd_timer(E) ghash_clmulni_intel(E) snd(E) > crct10dif_pclmul(E) virtio_balloon(E) serio_raw(E) soundcore(E) > crc32c_intel(E) qxl(E) drm_kms_helper(E) virtio_console(E) ttm(E) > virtio_net(E) net_failover(E) > [ 351.912077] failover(E) drm(E) qemu_fw_cfg(E) pata_acpi(E) > ata_generic(E) > [ 351.912888] CPU: 0 PID: 1483 Comm: bash Tainted: G E > 4.19.0-rc3+ #7 > [ 351.914221] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > BIOS ?-20180531_142017-buildhw-08.phx2.fedoraproject.org-1.fc28 > 04/01/2014 > [ 351.916582] RIP: 0010:pin_kill+0x128/0x140 > [ 351.917369] Code: f2 5a 00 48 8b 44 24 20 48 39 c5 0f 84 6f ff ff > ff 48 89 df e8 e9 4a 5b 00 8b 43 18 85 c0 7e b3 c6 03 00 fb 66 0f 1f > 44 00 00 <e9> 51 ff ff ff e8 be 11 dd ff 0f 1f 40 00 66 2e 0f 1f 84 00 > 00 00 > [ 351.920729] RSP: 0018:ffffa1b381be3d88 EFLAGS: 00000202 ORIG_RAX: > ffffffffffffff13 > [ 351.921801] RAX: 0000000000000000 RBX: ffff909cf2ea68b0 RCX: > dead000000000200 > [ 351.922807] RDX: 0000000000000001 RSI: ffffa1b381be3d28 RDI: > ffff909cf2ea68b0 > [ 351.923811] RBP: ffffa1b381be3da8 R08: ffff909d59621760 R09: > 0000000000000000 > [ 351.924813] R10: 0000000000000000 R11: 0000000000000000 R12: > 0000000010000000 > [ 351.925818] R13: ffff909cf5db9a38 R14: ffff909cf2ea67a0 R15: > ffff909cedc07300 > [ 351.926824] FS: 00007f1eb90ac740(0000) GS:ffff909d59600000(0000) > knlGS:0000000000000000 > [ 351.927957] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 351.928772] CR2: 00007f1eabedb180 CR3: 000000000f20a003 CR4: > 00000000003606f0 > [ 351.929779] DR0: 0000000000000000 DR1: 0000000000000000 DR2: > 0000000000000000 > [ 351.930785] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: > 0000000000000400 > [ 351.931791] Call Trace: > [ 351.932160] ? finish_wait+0x80/0x80 > [ 351.932684] group_pin_kill+0x1a/0x30 > [ 351.933207] namespace_unlock+0x6f/0x80 > [ 351.933766] __fput+0x239/0x240 > [ 351.934217] task_work_run+0x84/0xa0 > [ 351.934743] do_exit+0x2d3/0xae0 > [ 351.935206] ? __do_page_fault+0x263/0x4e0 > [ 351.935799] do_group_exit+0x3a/0xa0 > [ 351.936307] __x64_sys_exit_group+0x14/0x20 > [ 351.936911] do_syscall_64+0x5b/0x160 > [ 351.937436] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > [ 351.938164] RIP: 0033:0x7f1eb877adb6 > [ 351.938688] Code: Bad RIP value. > [ 351.939149] RSP: 002b:00007ffd56e019d8 EFLAGS: 00000246 ORIG_RAX: > 00000000000000e7 > [ 351.940216] RAX: ffffffffffffffda RBX: 00007f1eb8a69740 RCX: > 00007f1eb877adb6 > [ 351.941222] RDX: 0000000000000000 RSI: 000000000000003c RDI: > 0000000000000000 > [ 351.942229] RBP: 0000000000000000 R08: 00000000000000e7 R09: > ffffffffffffff80 > [ 351.943236] R10: 00007ffd56e0188a R11: 0000000000000246 R12: > 00007f1eb8a69740 > [ 351.944242] R13: 0000000000000001 R14: 00007f1eb8a72708 R15: > 0000000000000000 > >
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