Re: [RFC][PATCH] ecryptfs: Allow only one instance per lower path

From: Tyler Hicks
Date: Sat Aug 01 2015 - 21:03:12 EST

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 â/mnt_b/secret/xxxâ: 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@xxxxxx>
> ---
> 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
>

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