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Message-ID: <20200804140558.GF32719@miu.piliscsaba.redhat.com>
Date: Tue, 4 Aug 2020 16:05:58 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: David Howells <dhowells@...hat.com>
Cc: viro@...iv.linux.org.uk, torvalds@...ux-foundation.org,
raven@...maw.net, mszeredi@...hat.com, christian@...uner.io,
jannh@...gle.com, darrick.wong@...cle.com, kzak@...hat.com,
jlayton@...hat.com, linux-api@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/18] fsinfo: Add an attribute that lists all the
visible mounts in a namespace [ver #21]
On Mon, Aug 03, 2020 at 02:38:34PM +0100, David Howells wrote:
> Add a filesystem attribute that exports a list of all the visible mounts in
> a namespace, given the caller's chroot setting. The returned list is an
> array of:
>
> struct fsinfo_mount_child {
> __u64 mnt_unique_id;
> __u32 mnt_id;
> __u32 parent_id;
> __u32 mnt_notify_sum;
> __u32 sb_notify_sum;
> };
>
> where each element contains a once-in-a-system-lifetime unique ID, the
> mount ID (which may get reused), the parent mount ID and sums of the
> notification/change counters for the mount and its superblock.
The change counters are currently conditional on CONFIG_MOUNT_NOTIFICATIONS.
Is this is intentional?
>
> This works with a read lock on the namespace_sem, but ideally would do it
> under the RCU read lock only.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
>
> fs/fsinfo.c | 1 +
> fs/internal.h | 1 +
> fs/namespace.c | 37 +++++++++++++++++++++++++++++++++++++
> include/uapi/linux/fsinfo.h | 4 ++++
> samples/vfs/test-fsinfo.c | 22 ++++++++++++++++++++++
> 5 files changed, 65 insertions(+)
>
> diff --git a/fs/fsinfo.c b/fs/fsinfo.c
> index 0540cce89555..f230124ffdf5 100644
> --- a/fs/fsinfo.c
> +++ b/fs/fsinfo.c
> @@ -296,6 +296,7 @@ static const struct fsinfo_attribute fsinfo_common_attributes[] = {
> FSINFO_STRING (FSINFO_ATTR_MOUNT_POINT, fsinfo_generic_mount_point),
> FSINFO_STRING (FSINFO_ATTR_MOUNT_POINT_FULL, fsinfo_generic_mount_point_full),
> FSINFO_LIST (FSINFO_ATTR_MOUNT_CHILDREN, fsinfo_generic_mount_children),
> + FSINFO_LIST (FSINFO_ATTR_MOUNT_ALL, fsinfo_generic_mount_all),
> {}
> };
>
> diff --git a/fs/internal.h b/fs/internal.h
> index cb5edcc7125a..267b4aaf0271 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -102,6 +102,7 @@ extern int fsinfo_generic_mount_topology(struct path *, struct fsinfo_context *)
> extern int fsinfo_generic_mount_point(struct path *, struct fsinfo_context *);
> extern int fsinfo_generic_mount_point_full(struct path *, struct fsinfo_context *);
> extern int fsinfo_generic_mount_children(struct path *, struct fsinfo_context *);
> +extern int fsinfo_generic_mount_all(struct path *, struct fsinfo_context *);
>
> /*
> * fs_struct.c
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 122c12f9512b..1f2e06507244 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -4494,4 +4494,41 @@ int fsinfo_generic_mount_children(struct path *path, struct fsinfo_context *ctx)
> return ctx->usage;
> }
>
> +/*
> + * Return information about all the mounts in the namespace referenced by the
> + * path.
> + */
> +int fsinfo_generic_mount_all(struct path *path, struct fsinfo_context *ctx)
> +{
> + struct mnt_namespace *ns;
> + struct mount *m, *p;
> + struct path chroot;
> + bool allow;
> +
> + m = real_mount(path->mnt);
> + ns = m->mnt_ns;
> +
> + get_fs_root(current->fs, &chroot);
> + rcu_read_lock();
> + allow = are_paths_connected(&chroot, path) || capable(CAP_SYS_ADMIN);
> + rcu_read_unlock();
> + path_put(&chroot);
> + if (!allow)
> + return -EPERM;
> +
> + down_read(&namespace_sem);
> +
> + list_for_each_entry(p, &ns->list, mnt_list) {
This is missing locking and check added by commit 9f6c61f96f2d ("proc/mounts:
add cursor").
> + struct path mnt_root;
> +
> + mnt_root.mnt = &p->mnt;
> + mnt_root.dentry = p->mnt.mnt_root;
> + if (are_paths_connected(path, &mnt_root))
> + fsinfo_store_mount(ctx, p, p == m);
> + }
> +
> + up_read(&namespace_sem);
> + return ctx->usage;
> +}
> +
> #endif /* CONFIG_FSINFO */
> diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
> index 81329de6905e..e40192d98648 100644
> --- a/include/uapi/linux/fsinfo.h
> +++ b/include/uapi/linux/fsinfo.h
> @@ -37,6 +37,7 @@
> #define FSINFO_ATTR_MOUNT_POINT_FULL 0x203 /* Absolute path of mount (string) */
> #define FSINFO_ATTR_MOUNT_TOPOLOGY 0x204 /* Mount object topology */
> #define FSINFO_ATTR_MOUNT_CHILDREN 0x205 /* Children of this mount (list) */
> +#define FSINFO_ATTR_MOUNT_ALL 0x206 /* List all mounts in a namespace (list) */
>
> #define FSINFO_ATTR_AFS_CELL_NAME 0x300 /* AFS cell name (string) */
> #define FSINFO_ATTR_AFS_SERVER_NAME 0x301 /* Name of the Nth server (string) */
> @@ -128,6 +129,8 @@ struct fsinfo_mount_topology {
> /*
> * Information struct element for fsinfo(FSINFO_ATTR_MOUNT_CHILDREN).
> * - An extra element is placed on the end representing the parent mount.
> + *
> + * Information struct element for fsinfo(FSINFO_ATTR_MOUNT_ALL).
> */
> struct fsinfo_mount_child {
> __u64 mnt_unique_id; /* Kernel-lifetime unique mount ID */
> @@ -139,6 +142,7 @@ struct fsinfo_mount_child {
> };
>
> #define FSINFO_ATTR_MOUNT_CHILDREN__STRUCT struct fsinfo_mount_child
> +#define FSINFO_ATTR_MOUNT_ALL__STRUCT struct fsinfo_mount_child
>
> /*
> * Information struct for fsinfo(FSINFO_ATTR_STATFS).
> diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
> index 374825ab85b0..596fa5e71762 100644
> --- a/samples/vfs/test-fsinfo.c
> +++ b/samples/vfs/test-fsinfo.c
> @@ -365,6 +365,27 @@ static void dump_fsinfo_generic_mount_children(void *reply, unsigned int size)
> (unsigned long long)r->mnt_notify_sum, mp);
> }
>
> +static void dump_fsinfo_generic_mount_all(void *reply, unsigned int size)
> +{
> + struct fsinfo_mount_child *r = reply;
> + ssize_t mplen;
> + char path[32], *mp;
> +
> + struct fsinfo_params params = {
> + .flags = FSINFO_FLAGS_QUERY_MOUNT,
> + .request = FSINFO_ATTR_MOUNT_POINT_FULL,
> + };
> +
> + sprintf(path, "%u", r->mnt_id);
> + mplen = get_fsinfo(path, "FSINFO_ATTR_MOUNT_POINT_FULL", ¶ms, (void **)&mp);
> + if (mplen < 0)
> + mp = "-";
> +
> + printf("%5x %5x %12llx %10llu %s\n",
> + r->mnt_id, r->parent_id, (unsigned long long)r->mnt_unique_id,
> + r->mnt_notify_sum, mp);
> +}
> +
> static void dump_afs_fsinfo_server_address(void *reply, unsigned int size)
> {
> struct fsinfo_afs_server_address *f = reply;
> @@ -492,6 +513,7 @@ static const struct fsinfo_attribute fsinfo_attributes[] = {
> FSINFO_STRING_N (FSINFO_ATTR_MOUNT_POINT, string),
> FSINFO_STRING_N (FSINFO_ATTR_MOUNT_POINT_FULL, string),
> FSINFO_LIST (FSINFO_ATTR_MOUNT_CHILDREN, fsinfo_generic_mount_children),
> + FSINFO_LIST (FSINFO_ATTR_MOUNT_ALL, fsinfo_generic_mount_all),
>
> FSINFO_STRING (FSINFO_ATTR_AFS_CELL_NAME, string),
> FSINFO_STRING (FSINFO_ATTR_AFS_SERVER_NAME, string),
>
>
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