This patch allows to have multiple procfs instances inside the
same pid namespace. The aim here is lightweight sandboxes, and to allow
that we have to modernize procfs internals.
1) The main aim of this work is to have on embedded systems one
supervisor for apps. Right now we have some lightweight sandbox support,
however if we create pid namespacess we have to manages all the
processes inside too, where our goal is to be able to run a bunch of
apps each one inside its own mount namespace without being able to
notice each other. We only want to use mount namespaces, and we want
procfs to behave more like a real mount point.
2) Linux Security Modules have multiple ptrace paths inside some
subsystems, however inside procfs, the implementation does not guarantee
that the ptrace() check which triggers the security_ptrace_check() hook
will always run. We have the 'hidepid' mount option that can be used to
force the ptrace_may_access() check inside has_pid_permissions() to run.
The problem is that 'hidepid' is per pid namespace and not attached to
the mount point, any remount or modification of 'hidepid' will propagate
to all other procfs mounts.
This also does not allow to support Yama LSM easily in desktop and user
sessions. Yama ptrace scope which restricts ptrace and some other
syscalls to be allowed only on inferiors, can be updated to have a
per-task context, where the context will be inherited during fork(),
clone() and preserved across execve(). If we support multiple private
procfs instances, then we may force the ptrace_may_access() on
/proc/<pids>/ to always run inside that new procfs instances. This will
allow to specifiy on user sessions if we should populate procfs with
pids that the user can ptrace or not.
By using Yama ptrace scope, some restricted users will only be able to see
inferiors inside /proc, they won't even be able to see their other
processes. Some software like Chromium, Firefox's crash handler, Wine
and others are already using Yama to restrict which processes can be
ptracable. With this change this will give the possibility to restrict
/proc/<pids>/ but more importantly this will give desktop users a
generic and usuable way to specifiy which users should see all processes
and which users can not.
Side notes:
* This covers the lack of seccomp where it is not able to parse
arguments, it is easy to install a seccomp filter on direct syscalls
that operate on pids, however /proc/<pid>/ is a Linux ABI using
filesystem syscalls. With this change LSMs should be able to analyze
open/read/write/close...
In the new patchset version I removed the 'newinstance' option
as suggested by Eric W. Biederman.
Signed-off-by: Alexey Gladkov <[email protected]>
Reviewed-by: Alexey Dobriyan <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
---
fs/proc/base.c | 13 +++++++----
fs/proc/inode.c | 4 ++--
fs/proc/root.c | 42 ++++++++++++++++++++++-------------
fs/proc/self.c | 6 ++---
fs/proc/thread_self.c | 6 ++---
include/linux/pid_namespace.h | 4 ----
include/linux/proc_fs.h | 12 ++++++++++
7 files changed, 55 insertions(+), 32 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 74f948a6b621..3b9155a69ade 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3301,6 +3301,7 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
{
struct task_struct *task;
unsigned tgid;
+ struct proc_fs_info *fs_info;
struct pid_namespace *ns;
struct dentry *result = ERR_PTR(-ENOENT);
@@ -3308,7 +3309,8 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
if (tgid == ~0U)
goto out;
- ns = dentry->d_sb->s_fs_info;
+ fs_info = proc_sb_info(dentry->d_sb);
+ ns = fs_info->pid_ns;
rcu_read_lock();
task = find_task_by_pid_ns(tgid, ns);
if (task)
@@ -3372,6 +3374,7 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
int proc_pid_readdir(struct file *file, struct dir_context *ctx)
{
struct tgid_iter iter;
+ struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
struct pid_namespace *ns = proc_pid_ns(file_inode(file));
loff_t pos = ctx->pos;
@@ -3379,13 +3382,13 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
return 0;
if (pos == TGID_OFFSET - 2) {
- struct inode *inode = d_inode(ns->proc_self);
+ struct inode *inode = d_inode(fs_info->proc_self);
if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
return 0;
ctx->pos = pos = pos + 1;
}
if (pos == TGID_OFFSET - 1) {
- struct inode *inode = d_inode(ns->proc_thread_self);
+ struct inode *inode = d_inode(fs_info->proc_thread_self);
if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
return 0;
ctx->pos = pos = pos + 1;
@@ -3599,6 +3602,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
struct task_struct *task;
struct task_struct *leader = get_proc_task(dir);
unsigned tid;
+ struct proc_fs_info *fs_info;
struct pid_namespace *ns;
struct dentry *result = ERR_PTR(-ENOENT);
@@ -3609,7 +3613,8 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
if (tid == ~0U)
goto out;
- ns = dentry->d_sb->s_fs_info;
+ fs_info = proc_sb_info(dentry->d_sb);
+ ns = fs_info->pid_ns;
rcu_read_lock();
task = find_task_by_pid_ns(tid, ns);
if (task)
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 1e730ea1dcd6..6e4c6728338b 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -167,8 +167,8 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock
static int proc_show_options(struct seq_file *seq, struct dentry *root)
{
- struct super_block *sb = root->d_sb;
- struct pid_namespace *pid = sb->s_fs_info;
+ struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
+ struct pid_namespace *pid = fs_info->pid_ns;
if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 2633f10446c3..b28adbb0b937 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -30,7 +30,7 @@
#include "internal.h"
struct proc_fs_context {
- struct pid_namespace *pid_ns;
+ struct proc_fs_info *fs_info;
unsigned int mask;
int hidepid;
int gid;
@@ -92,7 +92,8 @@ static void proc_apply_options(struct super_block *s,
static int proc_fill_super(struct super_block *s, struct fs_context *fc)
{
- struct pid_namespace *pid_ns = get_pid_ns(s->s_fs_info);
+ struct proc_fs_context *ctx = fc->fs_private;
+ struct pid_namespace *pid_ns = get_pid_ns(ctx->fs_info->pid_ns);
struct inode *root_inode;
int ret;
@@ -106,6 +107,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
s->s_magic = PROC_SUPER_MAGIC;
s->s_op = &proc_sops;
s->s_time_gran = 1;
+ s->s_fs_info = ctx->fs_info;
/*
* procfs isn't actually a stacking filesystem; however, there is
@@ -113,7 +115,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
* top of it
*/
s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
-
+
/* procfs dentries and inodes don't require IO to create */
s->s_shrink.seeks = 0;
@@ -140,7 +142,8 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
static int proc_reconfigure(struct fs_context *fc)
{
struct super_block *sb = fc->root->d_sb;
- struct pid_namespace *pid = sb->s_fs_info;
+ struct proc_fs_info *fs_info = proc_sb_info(sb);
+ struct pid_namespace *pid = fs_info->pid_ns;
sync_filesystem(sb);
@@ -150,16 +153,14 @@ static int proc_reconfigure(struct fs_context *fc)
static int proc_get_tree(struct fs_context *fc)
{
- struct proc_fs_context *ctx = fc->fs_private;
-
- return get_tree_keyed(fc, proc_fill_super, ctx->pid_ns);
+ return get_tree_nodev(fc, proc_fill_super);
}
static void proc_fs_context_free(struct fs_context *fc)
{
struct proc_fs_context *ctx = fc->fs_private;
- put_pid_ns(ctx->pid_ns);
+ put_pid_ns(ctx->fs_info->pid_ns);
kfree(ctx);
}
@@ -178,9 +179,15 @@ static int proc_init_fs_context(struct fs_context *fc)
if (!ctx)
return -ENOMEM;
- ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
+ ctx->fs_info = kzalloc(sizeof(struct proc_fs_info), GFP_KERNEL);
+ if (!ctx->fs_info) {
+ kfree(ctx);
+ return -ENOMEM;
+ }
+
+ ctx->fs_info->pid_ns = get_pid_ns(task_active_pid_ns(current));
put_user_ns(fc->user_ns);
- fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
+ fc->user_ns = get_user_ns(ctx->fs_info->pid_ns->user_ns);
fc->fs_private = ctx;
fc->ops = &proc_fs_context_ops;
return 0;
@@ -188,15 +195,18 @@ static int proc_init_fs_context(struct fs_context *fc)
static void proc_kill_sb(struct super_block *sb)
{
- struct pid_namespace *ns;
+ struct proc_fs_info *fs_info = proc_sb_info(sb);
+ struct pid_namespace *ns = fs_info->pid_ns;
+
+ if (fs_info->proc_self)
+ dput(fs_info->proc_self);
+
+ if (fs_info->proc_thread_self)
+ dput(fs_info->proc_thread_self);
- ns = (struct pid_namespace *)sb->s_fs_info;
- if (ns->proc_self)
- dput(ns->proc_self);
- if (ns->proc_thread_self)
- dput(ns->proc_thread_self);
kill_anon_super(sb);
put_pid_ns(ns);
+ kfree(fs_info);
}
static struct file_system_type proc_fs_type = {
diff --git a/fs/proc/self.c b/fs/proc/self.c
index 57c0a1047250..309301ac0136 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -36,10 +36,10 @@ static unsigned self_inum __ro_after_init;
int proc_setup_self(struct super_block *s)
{
struct inode *root_inode = d_inode(s->s_root);
- struct pid_namespace *ns = proc_pid_ns(root_inode);
+ struct proc_fs_info *fs_info = proc_sb_info(s);
struct dentry *self;
int ret = -ENOMEM;
-
+
inode_lock(root_inode);
self = d_alloc_name(s->s_root, "self");
if (self) {
@@ -62,7 +62,7 @@ int proc_setup_self(struct super_block *s)
if (ret)
pr_err("proc_fill_super: can't allocate /proc/self\n");
else
- ns->proc_self = self;
+ fs_info->proc_self = self;
return ret;
}
diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
index f61ae53533f5..2493cbbdfa6f 100644
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c
@@ -36,7 +36,7 @@ static unsigned thread_self_inum __ro_after_init;
int proc_setup_thread_self(struct super_block *s)
{
struct inode *root_inode = d_inode(s->s_root);
- struct pid_namespace *ns = proc_pid_ns(root_inode);
+ struct proc_fs_info *fs_info = proc_sb_info(s);
struct dentry *thread_self;
int ret = -ENOMEM;
@@ -60,9 +60,9 @@ int proc_setup_thread_self(struct super_block *s)
inode_unlock(root_inode);
if (ret)
- pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
+ pr_err("proc_fill_super: can't allocate /proc/thread-self\n");
else
- ns->proc_thread_self = thread_self;
+ fs_info->proc_thread_self = thread_self;
return ret;
}
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 4956e362e55e..de4534d93cb6 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -32,10 +32,6 @@ struct pid_namespace {
struct kmem_cache *pid_cachep;
unsigned int level;
struct pid_namespace *parent;
-#ifdef CONFIG_PROC_FS
- struct dentry *proc_self;
- struct dentry *proc_thread_self;
-#endif
#ifdef CONFIG_BSD_PROCESS_ACCT
struct fs_pin *bacct;
#endif
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 40a7982b7285..5920a4ecd71b 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -27,6 +27,17 @@ struct proc_ops {
unsigned long (*proc_get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
};
+struct proc_fs_info {
+ struct pid_namespace *pid_ns;
+ struct dentry *proc_self; /* For /proc/self */
+ struct dentry *proc_thread_self; /* For /proc/thread-self */
+};
+
+static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
+{
+ return sb->s_fs_info;
+}
+
#ifdef CONFIG_PROC_FS
typedef int (*proc_write_t)(struct file *, char *, size_t);
@@ -161,6 +172,7 @@ int open_related_ns(struct ns_common *ns,
/* get the associated pid namespace for a file in procfs */
static inline struct pid_namespace *proc_pid_ns(const struct inode *inode)
{
+ return proc_sb_info(inode->i_sb)->pid_ns;
return inode->i_sb->s_fs_info;
}
--
2.25.2
Alexey Gladkov <[email protected]> writes:
> This patch allows to have multiple procfs instances inside the
> same pid namespace. The aim here is lightweight sandboxes, and to allow
> that we have to modernize procfs internals.
>
> 1) The main aim of this work is to have on embedded systems one
> supervisor for apps. Right now we have some lightweight sandbox support,
> however if we create pid namespacess we have to manages all the
> processes inside too, where our goal is to be able to run a bunch of
> apps each one inside its own mount namespace without being able to
> notice each other. We only want to use mount namespaces, and we want
> procfs to behave more like a real mount point.
>
> 2) Linux Security Modules have multiple ptrace paths inside some
> subsystems, however inside procfs, the implementation does not guarantee
> that the ptrace() check which triggers the security_ptrace_check() hook
> will always run. We have the 'hidepid' mount option that can be used to
> force the ptrace_may_access() check inside has_pid_permissions() to run.
> The problem is that 'hidepid' is per pid namespace and not attached to
> the mount point, any remount or modification of 'hidepid' will propagate
> to all other procfs mounts.
>
> This also does not allow to support Yama LSM easily in desktop and user
> sessions. Yama ptrace scope which restricts ptrace and some other
> syscalls to be allowed only on inferiors, can be updated to have a
> per-task context, where the context will be inherited during fork(),
> clone() and preserved across execve(). If we support multiple private
> procfs instances, then we may force the ptrace_may_access() on
> /proc/<pids>/ to always run inside that new procfs instances. This will
> allow to specifiy on user sessions if we should populate procfs with
> pids that the user can ptrace or not.
>
> By using Yama ptrace scope, some restricted users will only be able to see
> inferiors inside /proc, they won't even be able to see their other
> processes. Some software like Chromium, Firefox's crash handler, Wine
> and others are already using Yama to restrict which processes can be
> ptracable. With this change this will give the possibility to restrict
> /proc/<pids>/ but more importantly this will give desktop users a
> generic and usuable way to specifiy which users should see all processes
> and which users can not.
>
> Side notes:
> * This covers the lack of seccomp where it is not able to parse
> arguments, it is easy to install a seccomp filter on direct syscalls
> that operate on pids, however /proc/<pid>/ is a Linux ABI using
> filesystem syscalls. With this change LSMs should be able to analyze
> open/read/write/close...
>
> In the new patchset version I removed the 'newinstance' option
> as suggested by Eric W. Biederman.
Some very small requests.
1) Can you please not place fs_info in fs_context, and instead allocate
fs_info in fill_super? Unless I have misread introduced a resource
leak if proc is not mounted or if proc is simply reconfigured.
2) Can you please move hide_pid and pid_gid into fs_info in this patch?
As was shown by my recent bug fix
3) Can you please rebase on on v5.7-rc1 or v5.7-rc2 and repost these
patches please? I thought I could do it safely but between my bug
fixes, and Alexey Dobriyan's parallel changes to proc these patches
do not apply cleanly.
Plus there is a resource leak in this patch.
Eric
> Signed-off-by: Alexey Gladkov <[email protected]>
> Reviewed-by: Alexey Dobriyan <[email protected]>
> Reviewed-by: Kees Cook <[email protected]>
> ---
> fs/proc/base.c | 13 +++++++----
> fs/proc/inode.c | 4 ++--
> fs/proc/root.c | 42 ++++++++++++++++++++++-------------
> fs/proc/self.c | 6 ++---
> fs/proc/thread_self.c | 6 ++---
> include/linux/pid_namespace.h | 4 ----
> include/linux/proc_fs.h | 12 ++++++++++
> 7 files changed, 55 insertions(+), 32 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 74f948a6b621..3b9155a69ade 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3301,6 +3301,7 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
> {
> struct task_struct *task;
> unsigned tgid;
> + struct proc_fs_info *fs_info;
> struct pid_namespace *ns;
> struct dentry *result = ERR_PTR(-ENOENT);
>
> @@ -3308,7 +3309,8 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
> if (tgid == ~0U)
> goto out;
>
> - ns = dentry->d_sb->s_fs_info;
> + fs_info = proc_sb_info(dentry->d_sb);
> + ns = fs_info->pid_ns;
> rcu_read_lock();
> task = find_task_by_pid_ns(tgid, ns);
> if (task)
> @@ -3372,6 +3374,7 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
> int proc_pid_readdir(struct file *file, struct dir_context *ctx)
> {
> struct tgid_iter iter;
> + struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
> struct pid_namespace *ns = proc_pid_ns(file_inode(file));
> loff_t pos = ctx->pos;
>
> @@ -3379,13 +3382,13 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
> return 0;
>
> if (pos == TGID_OFFSET - 2) {
> - struct inode *inode = d_inode(ns->proc_self);
> + struct inode *inode = d_inode(fs_info->proc_self);
> if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
> return 0;
> ctx->pos = pos = pos + 1;
> }
> if (pos == TGID_OFFSET - 1) {
> - struct inode *inode = d_inode(ns->proc_thread_self);
> + struct inode *inode = d_inode(fs_info->proc_thread_self);
> if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
> return 0;
> ctx->pos = pos = pos + 1;
> @@ -3599,6 +3602,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
> struct task_struct *task;
> struct task_struct *leader = get_proc_task(dir);
> unsigned tid;
> + struct proc_fs_info *fs_info;
> struct pid_namespace *ns;
> struct dentry *result = ERR_PTR(-ENOENT);
>
> @@ -3609,7 +3613,8 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
> if (tid == ~0U)
> goto out;
>
> - ns = dentry->d_sb->s_fs_info;
> + fs_info = proc_sb_info(dentry->d_sb);
> + ns = fs_info->pid_ns;
> rcu_read_lock();
> task = find_task_by_pid_ns(tid, ns);
> if (task)
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index 1e730ea1dcd6..6e4c6728338b 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -167,8 +167,8 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock
>
> static int proc_show_options(struct seq_file *seq, struct dentry *root)
> {
> - struct super_block *sb = root->d_sb;
> - struct pid_namespace *pid = sb->s_fs_info;
> + struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
> + struct pid_namespace *pid = fs_info->pid_ns;
>
> if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
> seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 2633f10446c3..b28adbb0b937 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -30,7 +30,7 @@
> #include "internal.h"
>
> struct proc_fs_context {
> - struct pid_namespace *pid_ns;
> + struct proc_fs_info *fs_info;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Please don't do this. As best as I can tell that introduces a memory
leak of proc is not mounted. Please allocate fs_info in
> unsigned int mask;
> int hidepid;
> int gid;
> @@ -92,7 +92,8 @@ static void proc_apply_options(struct super_block *s,
>
> static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> {
> - struct pid_namespace *pid_ns = get_pid_ns(s->s_fs_info);
> + struct proc_fs_context *ctx = fc->fs_private;
> + struct pid_namespace *pid_ns = get_pid_ns(ctx->fs_info->pid_ns);
> struct inode *root_inode;
> int ret;
>
> @@ -106,6 +107,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> s->s_magic = PROC_SUPER_MAGIC;
> s->s_op = &proc_sops;
> s->s_time_gran = 1;
> + s->s_fs_info = ctx->fs_info;
>
> /*
> * procfs isn't actually a stacking filesystem; however, there is
> @@ -113,7 +115,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> * top of it
> */
> s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
> -
> +
> /* procfs dentries and inodes don't require IO to create */
> s->s_shrink.seeks = 0;
>
> @@ -140,7 +142,8 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> static int proc_reconfigure(struct fs_context *fc)
> {
> struct super_block *sb = fc->root->d_sb;
> - struct pid_namespace *pid = sb->s_fs_info;
> + struct proc_fs_info *fs_info = proc_sb_info(sb);
> + struct pid_namespace *pid = fs_info->pid_ns;
>
> sync_filesystem(sb);
>
> @@ -150,16 +153,14 @@ static int proc_reconfigure(struct fs_context *fc)
>
> static int proc_get_tree(struct fs_context *fc)
> {
> - struct proc_fs_context *ctx = fc->fs_private;
> -
> - return get_tree_keyed(fc, proc_fill_super, ctx->pid_ns);
> + return get_tree_nodev(fc, proc_fill_super);
> }
>
> static void proc_fs_context_free(struct fs_context *fc)
> {
> struct proc_fs_context *ctx = fc->fs_private;
>
> - put_pid_ns(ctx->pid_ns);
> + put_pid_ns(ctx->fs_info->pid_ns);
> kfree(ctx);
> }
>
> @@ -178,9 +179,15 @@ static int proc_init_fs_context(struct fs_context *fc)
> if (!ctx)
> return -ENOMEM;
>
> - ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
> + ctx->fs_info = kzalloc(sizeof(struct proc_fs_info), GFP_KERNEL);
> + if (!ctx->fs_info) {
> + kfree(ctx);
> + return -ENOMEM;
> + }
> +
> + ctx->fs_info->pid_ns = get_pid_ns(task_active_pid_ns(current));
> put_user_ns(fc->user_ns);
> - fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
> + fc->user_ns = get_user_ns(ctx->fs_info->pid_ns->user_ns);
> fc->fs_private = ctx;
> fc->ops = &proc_fs_context_ops;
> return 0;
> @@ -188,15 +195,18 @@ static int proc_init_fs_context(struct fs_context *fc)
>
> static void proc_kill_sb(struct super_block *sb)
> {
> - struct pid_namespace *ns;
> + struct proc_fs_info *fs_info = proc_sb_info(sb);
> + struct pid_namespace *ns = fs_info->pid_ns;
> +
> + if (fs_info->proc_self)
> + dput(fs_info->proc_self);
> +
> + if (fs_info->proc_thread_self)
> + dput(fs_info->proc_thread_self);
>
> - ns = (struct pid_namespace *)sb->s_fs_info;
> - if (ns->proc_self)
> - dput(ns->proc_self);
> - if (ns->proc_thread_self)
> - dput(ns->proc_thread_self);
> kill_anon_super(sb);
> put_pid_ns(ns);
> + kfree(fs_info);
> }
>
> static struct file_system_type proc_fs_type = {
> diff --git a/fs/proc/self.c b/fs/proc/self.c
> index 57c0a1047250..309301ac0136 100644
> --- a/fs/proc/self.c
> +++ b/fs/proc/self.c
> @@ -36,10 +36,10 @@ static unsigned self_inum __ro_after_init;
> int proc_setup_self(struct super_block *s)
> {
> struct inode *root_inode = d_inode(s->s_root);
> - struct pid_namespace *ns = proc_pid_ns(root_inode);
> + struct proc_fs_info *fs_info = proc_sb_info(s);
> struct dentry *self;
> int ret = -ENOMEM;
> -
> +
> inode_lock(root_inode);
> self = d_alloc_name(s->s_root, "self");
> if (self) {
> @@ -62,7 +62,7 @@ int proc_setup_self(struct super_block *s)
> if (ret)
> pr_err("proc_fill_super: can't allocate /proc/self\n");
> else
> - ns->proc_self = self;
> + fs_info->proc_self = self;
>
> return ret;
> }
> diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
> index f61ae53533f5..2493cbbdfa6f 100644
> --- a/fs/proc/thread_self.c
> +++ b/fs/proc/thread_self.c
> @@ -36,7 +36,7 @@ static unsigned thread_self_inum __ro_after_init;
> int proc_setup_thread_self(struct super_block *s)
> {
> struct inode *root_inode = d_inode(s->s_root);
> - struct pid_namespace *ns = proc_pid_ns(root_inode);
> + struct proc_fs_info *fs_info = proc_sb_info(s);
> struct dentry *thread_self;
> int ret = -ENOMEM;
>
> @@ -60,9 +60,9 @@ int proc_setup_thread_self(struct super_block *s)
> inode_unlock(root_inode);
>
> if (ret)
> - pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
> + pr_err("proc_fill_super: can't allocate /proc/thread-self\n");
> else
> - ns->proc_thread_self = thread_self;
> + fs_info->proc_thread_self = thread_self;
>
> return ret;
> }
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 4956e362e55e..de4534d93cb6 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -32,10 +32,6 @@ struct pid_namespace {
> struct kmem_cache *pid_cachep;
> unsigned int level;
> struct pid_namespace *parent;
> -#ifdef CONFIG_PROC_FS
> - struct dentry *proc_self;
> - struct dentry *proc_thread_self;
> -#endif
> #ifdef CONFIG_BSD_PROCESS_ACCT
> struct fs_pin *bacct;
> #endif
> diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
> index 40a7982b7285..5920a4ecd71b 100644
> --- a/include/linux/proc_fs.h
> +++ b/include/linux/proc_fs.h
> @@ -27,6 +27,17 @@ struct proc_ops {
> unsigned long (*proc_get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
> };
>
> +struct proc_fs_info {
> + struct pid_namespace *pid_ns;
> + struct dentry *proc_self; /* For /proc/self */
> + struct dentry *proc_thread_self; /* For /proc/thread-self */
> +};
> +
> +static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
> +{
> + return sb->s_fs_info;
> +}
> +
> #ifdef CONFIG_PROC_FS
>
> typedef int (*proc_write_t)(struct file *, char *, size_t);
> @@ -161,6 +172,7 @@ int open_related_ns(struct ns_common *ns,
> /* get the associated pid namespace for a file in procfs */
> static inline struct pid_namespace *proc_pid_ns(const struct inode *inode)
> {
> + return proc_sb_info(inode->i_sb)->pid_ns;
> return inode->i_sb->s_fs_info;
> }
On Fri, Apr 17, 2020 at 01:55:05PM -0500, Eric W. Biederman wrote:
> Alexey Gladkov <[email protected]> writes:
>
> > This patch allows to have multiple procfs instances inside the
> > same pid namespace. The aim here is lightweight sandboxes, and to allow
> > that we have to modernize procfs internals.
> >
> > 1) The main aim of this work is to have on embedded systems one
> > supervisor for apps. Right now we have some lightweight sandbox support,
> > however if we create pid namespacess we have to manages all the
> > processes inside too, where our goal is to be able to run a bunch of
> > apps each one inside its own mount namespace without being able to
> > notice each other. We only want to use mount namespaces, and we want
> > procfs to behave more like a real mount point.
> >
> > 2) Linux Security Modules have multiple ptrace paths inside some
> > subsystems, however inside procfs, the implementation does not guarantee
> > that the ptrace() check which triggers the security_ptrace_check() hook
> > will always run. We have the 'hidepid' mount option that can be used to
> > force the ptrace_may_access() check inside has_pid_permissions() to run.
> > The problem is that 'hidepid' is per pid namespace and not attached to
> > the mount point, any remount or modification of 'hidepid' will propagate
> > to all other procfs mounts.
> >
> > This also does not allow to support Yama LSM easily in desktop and user
> > sessions. Yama ptrace scope which restricts ptrace and some other
> > syscalls to be allowed only on inferiors, can be updated to have a
> > per-task context, where the context will be inherited during fork(),
> > clone() and preserved across execve(). If we support multiple private
> > procfs instances, then we may force the ptrace_may_access() on
> > /proc/<pids>/ to always run inside that new procfs instances. This will
> > allow to specifiy on user sessions if we should populate procfs with
> > pids that the user can ptrace or not.
> >
> > By using Yama ptrace scope, some restricted users will only be able to see
> > inferiors inside /proc, they won't even be able to see their other
> > processes. Some software like Chromium, Firefox's crash handler, Wine
> > and others are already using Yama to restrict which processes can be
> > ptracable. With this change this will give the possibility to restrict
> > /proc/<pids>/ but more importantly this will give desktop users a
> > generic and usuable way to specifiy which users should see all processes
> > and which users can not.
> >
> > Side notes:
> > * This covers the lack of seccomp where it is not able to parse
> > arguments, it is easy to install a seccomp filter on direct syscalls
> > that operate on pids, however /proc/<pid>/ is a Linux ABI using
> > filesystem syscalls. With this change LSMs should be able to analyze
> > open/read/write/close...
> >
> > In the new patchset version I removed the 'newinstance' option
> > as suggested by Eric W. Biederman.
>
> Some very small requests.
>
> 1) Can you please not place fs_info in fs_context, and instead allocate
> fs_info in fill_super? Unless I have misread introduced a resource
> leak if proc is not mounted or if proc is simply reconfigured.
Hm ... it seems you're right.
> 2) Can you please move hide_pid and pid_gid into fs_info in this patch?
> As was shown by my recent bug fix
OK. I’ll do it in the next version.
> 3) Can you please rebase on on v5.7-rc1 or v5.7-rc2 and repost these
> patches please? I thought I could do it safely but between my bug
> fixes, and Alexey Dobriyan's parallel changes to proc these patches
> do not apply cleanly.
>
> Plus there is a resource leak in this patch.
On my way.
> > struct proc_fs_context {
> > - struct pid_namespace *pid_ns;
> > + struct proc_fs_info *fs_info;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Please don't do this. As best as I can tell that introduces a memory
> leak of proc is not mounted. Please allocate fs_info in
OK.
--
Rgrds, legion