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    SubjectRe: [RFC][PATCH] ecryptfs: Allow only one instance per lower path
    Thanks for the report and for the patch, Richard!

    On 2015-07-31 12:23:10, Richard Weinberger wrote:
    > Mounting the same lower path multiple times should not result
    > into multiple ecryptfs instances, otherwise ecryptfs gets confused.
    >
    > A command sequence of:

    An important detail that took me a while to realize is that /tmp should
    be tmpfs in order to trigger the warnings below. I was unable to
    reproduce the warnings with ext4 as the lower filesystem.

    > $ mount -t ecryptfs /tmp/.secret /mnt_a/secret/
    > $ mount -t ecryptfs /tmp/.secret /mnt_b/secret/
    > $ mkdir -p /mnt_a/secret/xxx
    > $ mkdir -p /mnt_b/secret/xxx

    Note that the -p option is covering up the fact that /mnt_b/secret/xxx
    already exists. Remove that option and you should see this error:

    mkdir: cannot create directory ‘/mnt_b/secret/xxx’: File exists

    This really isn't important other than understanding that the second
    mkdir it isn't needed.

    > $ echo foo > /mnt_a/secret/xxx/test.txt
    > $ echo foo > /mnt_b/secret/xxx/test.txt

    /mnt_b/secret/xxx/test.txt should already exist (it does for me, at
    least) so the same file is being written to twice in a row. Again, not
    really important other than to know that it isn't needed.

    > $ rm -rf /mnt_a/secret/xxx
    > $ rm -rf /mnt_b/secret/xxx

    The /mnt_b/secret/xxx dcache entry is stale here because the underlying
    file was removed by the first rm command in the /mnt_a/secret mount. The
    lower inode's nlink is 0 at this point and what should be happening
    here, I think, is that the eCryptfs dentry should be invalidated and the
    eCryptfs inode should be destroyed.

    I think that the proper fix is to catch this condition in
    ecryptfs_d_revalidate(). I've started working on coming up with a patch
    for that but I'll need some more time to finish and test it.

    Tyler

    >
    > results into:
    > [ 125.536842] ------------[ cut here ]------------
    > [ 125.537981] WARNING: CPU: 0 PID: 2100 at fs/inode.c:275 drop_nlink+0x41/0x50()
    > [ 125.539694] Modules linked in:
    > [ 125.540481] CPU: 0 PID: 2100 Comm: rm Not tainted 4.2.0-rc3+ #67
    > [ 125.541909] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140816_022509-build35 04/01/2014
    > [ 125.544603] ffffffff81bd943b ffff88007ba67d08 ffffffff818b032f 0000000000000001
    > [ 125.546522] 0000000000000000 ffff88007ba67d48 ffffffff810502b7 ffff88007ba67d0a
    > [ 125.548443] ffff88007caa7c58 ffff88007b59aad8 ffff88007cc3e780 0000000000000000
    > [ 125.550224] Call Trace:
    > [ 125.550772] [<ffffffff818b032f>] dump_stack+0x45/0x57
    > [ 125.551929] [<ffffffff810502b7>] warn_slowpath_common+0x87/0xc0
    > [ 125.553281] [<ffffffff81050395>] warn_slowpath_null+0x15/0x20
    > [ 125.554588] [<ffffffff81178be1>] drop_nlink+0x41/0x50
    > [ 125.555744] [<ffffffff811252d8>] shmem_unlink+0x68/0x80
    > [ 125.556950] [<ffffffff8116b265>] vfs_unlink+0xd5/0x180
    > [ 125.558126] [<ffffffff81241d2f>] ecryptfs_do_unlink+0x6f/0x130
    > [ 125.559456] [<ffffffff81241dfd>] ecryptfs_unlink+0xd/0x10
    > [ 125.560701] [<ffffffff8116b265>] vfs_unlink+0xd5/0x180
    > [ 125.561814] [<ffffffff8116ece0>] do_unlinkat+0x240/0x290
    > [ 125.562954] [<ffffffff8116f5e6>] SyS_unlinkat+0x16/0x30
    > [ 125.564090] [<ffffffff818bac17>] entry_SYSCALL_64_fastpath+0x12/0x6a
    > [ 125.565447] ---[ end trace 7d3a7839aa1d00d2 ]---
    > [ 125.566432] ------------[ cut here ]------------
    > [ 125.567415] WARNING: CPU: 0 PID: 2100 at fs/dcache.c:309 dentry_free+0x73/0x90()
    > [ 125.568981] Modules linked in:
    > [ 125.569668] CPU: 0 PID: 2100 Comm: rm Tainted: G W 4.2.0-rc3+ #67
    > [ 125.571194] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140816_022509-build35 04/01/2014
    > [ 125.573538] ffffffff81bd5e7b ffff88007ba67d38 ffffffff818b032f 0000000000000001
    > [ 125.575111] 0000000000000000 ffff88007ba67d78 ffffffff810502b7 ffff88007cc3e780
    > [ 125.576671] ffff88007cc3e780 0000000000000000 ffff88007cc3e7d8 0000000000000000
    > [ 125.578239] Call Trace:
    > [ 125.578728] [<ffffffff818b032f>] dump_stack+0x45/0x57
    > [ 125.579768] [<ffffffff810502b7>] warn_slowpath_common+0x87/0xc0
    > [ 125.580977] [<ffffffff81050395>] warn_slowpath_null+0x15/0x20
    > [ 125.582152] [<ffffffff81174943>] dentry_free+0x73/0x90
    > [ 125.583200] [<ffffffff81175183>] __dentry_kill+0x153/0x1d0
    > [ 125.584323] [<ffffffff8117537f>] dput+0x17f/0x1d0
    > [ 125.585274] [<ffffffff81168e25>] path_put+0x15/0x30
    > [ 125.586230] [<ffffffff81240f5a>] ecryptfs_d_release+0x1a/0x40
    > [ 125.587335] [<ffffffff8117515f>] __dentry_kill+0x12f/0x1d0
    > [ 125.588400] [<ffffffff8117537f>] dput+0x17f/0x1d0
    > [ 125.589320] [<ffffffff8116ec27>] do_unlinkat+0x187/0x290
    > [ 125.590351] [<ffffffff8116f5e6>] SyS_unlinkat+0x16/0x30
    > [ 125.591359] [<ffffffff818bac17>] entry_SYSCALL_64_fastpath+0x12/0x6a
    > [ 125.592580] ---[ end trace 7d3a7839aa1d00d3 ]---
    > [ 125.604089] ------------[ cut here ]------------
    > [ 125.605005] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:2694 rcu_process_callbacks+0x4b7/0x570()
    > [ 125.605075] Modules linked in:
    > [ 125.605075] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 4.2.0-rc3+ #67
    > [ 125.605075] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140816_022509-build35 04/01/2014
    > [ 125.605075] ffffffff81bb9a07 ffff88007fc03e48 ffffffff818b032f 0000000000000000
    > [ 125.605075] 0000000000000000 ffff88007fc03e88 ffffffff810502b7 ffff88007fc03e78
    > [ 125.605075] ffffffff81e3f180 0000000000000246 0000000000000000 0000000000000001
    > [ 125.605075] Call Trace:
    > [ 125.605075] <IRQ> [<ffffffff818b032f>] dump_stack+0x45/0x57
    > [ 125.605075] [<ffffffff810502b7>] warn_slowpath_common+0x87/0xc0
    > [ 125.605075] [<ffffffff81050395>] warn_slowpath_null+0x15/0x20
    > [ 125.605075] [<ffffffff810a1487>] rcu_process_callbacks+0x4b7/0x570
    > [ 125.605075] [<ffffffff81053eb4>] __do_softirq+0xd4/0x250
    > [ 125.605075] [<ffffffff81054226>] irq_exit+0x86/0x90
    > [ 125.605075] [<ffffffff810377f5>] smp_apic_timer_interrupt+0x45/0x60
    > [ 125.605075] [<ffffffff818bb9e8>] apic_timer_interrupt+0x68/0x70
    > [ 125.605075] <EOI> [<ffffffff8100cf5b>] ? default_idle+0x1b/0xa0
    > [ 125.605075] [<ffffffff8100d4ba>] arch_cpu_idle+0xa/0x10
    > [ 125.605075] [<ffffffff81086f30>] default_idle_call+0x30/0x40
    > [ 125.605075] [<ffffffff81087199>] cpu_startup_entry+0x1f9/0x2e0
    > [ 125.605075] [<ffffffff818a9a87>] rest_init+0x77/0x80
    > [ 125.605075] [<ffffffff81f2dff5>] start_kernel+0x43e/0x44b
    > [ 125.605075] [<ffffffff81f2d99c>] ? set_init_arg+0x58/0x58
    > [ 125.605075] [<ffffffff81f2d5ad>] x86_64_start_reservations+0x2a/0x2c
    > [ 125.605075] [<ffffffff81f2d69b>] x86_64_start_kernel+0xec/0xf0
    > [ 125.605075] ---[ end trace 7d3a7839aa1d00d4 ]---
    >
    > Reuse the existing super block if the lower path is already mounted
    > to get rid of that issue.
    >
    > Signed-off-by: Richard Weinberger <richard@nod.at>
    > ---
    > Tyler,
    >
    > I'm not sure whether my fix is the correct solution.
    > Maybe ecryptfs supports mounting the same lower path mutliple times
    > and something else is broken.
    >
    > Thanks,
    > //richard
    > ---
    > fs/ecryptfs/main.c | 39 ++++++++++++++++++++++++++++-----------
    > 1 file changed, 28 insertions(+), 11 deletions(-)
    >
    > diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
    > index 4f4d047..bf6ad60 100644
    > --- a/fs/ecryptfs/main.c
    > +++ b/fs/ecryptfs/main.c
    > @@ -481,6 +481,15 @@ out:
    > struct kmem_cache *ecryptfs_sb_info_cache;
    > static struct file_system_type ecryptfs_fs_type;
    >
    > +static int sb_test(struct super_block *sb, void *data)
    > +{
    > + struct ecryptfs_dentry_info *info = sb->s_root->d_fsdata;
    > + struct path *p2 = &info->lower_path;
    > + struct path *p1 = data;
    > +
    > + return p1->dentry->d_inode == p2->dentry->d_inode;
    > +}
    > +
    > /**
    > * ecryptfs_get_sb
    > * @fs_type
    > @@ -514,15 +523,29 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
    > }
    > mount_crypt_stat = &sbi->mount_crypt_stat;
    >
    > - s = sget(fs_type, NULL, set_anon_super, flags, NULL);
    > + err = "Reading sb failed";
    > + rc = kern_path(dev_name, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
    > + if (rc) {
    > + ecryptfs_printk(KERN_WARNING, "kern_path() failed\n");
    > + goto out;
    > + }
    > +
    > + s = sget(fs_type, sb_test, set_anon_super, flags, &path);
    > if (IS_ERR(s)) {
    > rc = PTR_ERR(s);
    > - goto out;
    > + goto out_put;
    > + }
    > +
    > + if (s->s_root) {
    > + path_put(&path);
    > + ecryptfs_destroy_mount_crypt_stat(&sbi->mount_crypt_stat);
    > + kmem_cache_free(ecryptfs_sb_info_cache, sbi);
    > + return dget(s->s_root);
    > }
    >
    > rc = bdi_setup_and_register(&sbi->bdi, "ecryptfs");
    > if (rc)
    > - goto out1;
    > + goto out_free;
    >
    > ecryptfs_set_superblock_private(s, sbi);
    > s->s_bdi = &sbi->bdi;
    > @@ -532,12 +555,6 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
    > s->s_op = &ecryptfs_sops;
    > s->s_d_op = &ecryptfs_dops;
    >
    > - err = "Reading sb failed";
    > - rc = kern_path(dev_name, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
    > - if (rc) {
    > - ecryptfs_printk(KERN_WARNING, "kern_path() failed\n");
    > - goto out1;
    > - }
    > if (path.dentry->d_sb->s_type == &ecryptfs_fs_type) {
    > rc = -EINVAL;
    > printk(KERN_ERR "Mount on filesystem of type "
    > @@ -608,9 +625,9 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
    > return dget(s->s_root);
    >
    > out_free:
    > - path_put(&path);
    > -out1:
    > deactivate_locked_super(s);
    > +out_put:
    > + path_put(&path);
    > out:
    > if (sbi) {
    > ecryptfs_destroy_mount_crypt_stat(&sbi->mount_crypt_stat);
    > --
    > 1.8.4.5
    >
    [unhandled content-type:application/pgp-signature]
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