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Subject[PATCH v5 7/7] proc: add option to mount only a pids subset
This allows to hide all files and directories in the procfs that are not
related to tasks.

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
fs/proc/generic.c | 20 ++++++++++++++++++++
fs/proc/inode.c | 7 +++++++
fs/proc/root.c | 12 ++++++++++--
include/linux/proc_fs.h | 21 +++++++++++++++++++++
4 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 2078e70..af1295c 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -266,6 +266,11 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
unsigned int flags)
{
+ struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
+
+ if (proc_fs_pidonly(fs_info))
+ return ERR_PTR(-ENOENT);
+
return proc_lookup_de(dir, dentry, PDE(dir));
}

@@ -322,10 +327,24 @@ int proc_readdir_de(struct file *file, struct dir_context *ctx,
int proc_readdir(struct file *file, struct dir_context *ctx)
{
struct inode *inode = file_inode(file);
+ struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
+
+ if (proc_fs_pidonly(fs_info))
+ return 1;

return proc_readdir_de(file, ctx, PDE(inode));
}

+static int proc_dir_open(struct inode *inode, struct file *file)
+{
+ struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
+
+ if (proc_fs_pidonly(fs_info))
+ return -ENOENT;
+
+ return 0;
+}
+
/*
* These are the generic /proc directory operations. They
* use the in-memory "struct proc_dir_entry" tree to parse
@@ -335,6 +354,7 @@ static const struct file_operations proc_dir_operations = {
.llseek = generic_file_llseek,
.read = generic_read_dir,
.iterate_shared = proc_readdir,
+ .open = proc_dir_open,
};

/*
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 5e62598..9b7d9cb 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -125,6 +125,9 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
if (limit_pids > PROC_LIMIT_PIDS_OFF)
seq_printf(seq, ",limit_pids=%u", limit_pids);

+ if (proc_fs_pidonly(fs_info))
+ seq_printf(seq, ",pidonly");
+
return 0;
}

@@ -338,12 +341,16 @@ proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,

static int proc_reg_open(struct inode *inode, struct file *file)
{
+ struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
int (*open)(struct inode *, struct file *);
int (*release)(struct inode *, struct file *);
struct pde_opener *pdeo;

+ if (proc_fs_pidonly(fs_info))
+ return -ENOENT;
+
/*
* Ensure that
* 1) PDE's ->release hook will be called no matter what
diff --git a/fs/proc/root.c b/fs/proc/root.c
index c72d22c..daa318e 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -28,17 +28,18 @@
#include "internal.h"

enum {
- Opt_gid, Opt_hidepid, Opt_limit_pids, Opt_err,
+ Opt_gid, Opt_hidepid, Opt_limit_pids, Opt_pidonly, Opt_err,
};

static const match_table_t tokens = {
{Opt_hidepid, "hidepid=%u"},
{Opt_gid, "gid=%u"},
{Opt_limit_pids, "limit_pids=%u"},
+ {Opt_pidonly, "pidonly"},
{Opt_err, NULL},
};

-/* We only parse 'limit_pids' option here */
+/* We only parse 'limit_pids' and 'pidonly' option here */
int proc_parse_early_options(char *options, struct proc_fs_info *fs_info)
{
char *p, *opts, *orig;
@@ -74,6 +75,11 @@ int proc_parse_early_options(char *options, struct proc_fs_info *fs_info)
proc_fs_set_newinstance(fs_info, true);
pr_info("proc: mounting a new procfs instance ");
break;
+ case Opt_pidonly:
+ proc_fs_set_pidonly(fs_info, PROC_PIDONLY_ON);
+ proc_fs_set_newinstance(fs_info, true);
+ pr_info("proc: mounting a new procfs instance ");
+ break;
case Opt_gid:
case Opt_hidepid:
break;
@@ -126,6 +132,7 @@ int proc_parse_options(char *options, struct proc_fs_info *fs_info)
}
proc_fs_set_hide_pid(fs_info, option);
break;
+ case Opt_pidonly:
case Opt_limit_pids:
break;
default:
@@ -198,6 +205,7 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
/* Set it as early as possible */
proc_fs_set_newinstance(fs_info, false);
proc_fs_set_limit_pids(fs_info, PROC_LIMIT_PIDS_OFF);
+ proc_fs_set_pidonly(fs_info, PROC_PIDONLY_OFF);

if (flags & SB_KERNMOUNT) {
ns = data;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 70e8b10..77137c1 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -18,6 +18,11 @@ enum { /* definitions for proc mount option limit_pids */
PROC_LIMIT_PIDS_PTRACE = 1, /* Limit pids to only ptracable pids */
};

+enum {
+ PROC_PIDONLY_OFF = 0,
+ PROC_PIDONLY_ON = 1,
+};
+
struct proc_fs_info {
struct super_block *sb;
struct pid_namespace *pid_ns;
@@ -26,6 +31,7 @@ struct proc_fs_info {
struct dentry *proc_thread_self; /* For /proc/thread-self/ */
bool newinstance; /* Private flag for new separated instances */
int limit_pids:1;
+ int pidonly:1;
};

#ifdef CONFIG_PROC_FS
@@ -60,6 +66,16 @@ static inline int proc_fs_set_limit_pids(struct proc_fs_info *fs_info, int value
return 0;
}

+static inline int proc_fs_set_pidonly(struct proc_fs_info *fs_info, int value)
+{
+ if (value != PROC_PIDONLY_ON && value != PROC_PIDONLY_OFF)
+ return -EINVAL;
+
+ fs_info->pidonly = value;
+
+ return 0;
+}
+
static inline int proc_fs_hide_pid(struct proc_fs_info *fs_info)
{
return fs_info->pid_ns->hide_pid;
@@ -80,6 +96,11 @@ static inline int proc_fs_limit_pids(struct proc_fs_info *fs_info)
return fs_info->limit_pids;
}

+static inline int proc_fs_pidonly(struct proc_fs_info *fs_info)
+{
+ return fs_info->pidonly;
+}
+
extern void proc_root_init(void);
extern void proc_flush_task(struct task_struct *);

--
2.10.5
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