[PATCH RESEND v9 5/8] proc: add option to mount only a pids subset

Alexey Gladkov
2020-03-24T20:46:42Z

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 | 9 +++++++++
fs/proc/inode.c | 6 ++++++
fs/proc/root.c | 33 +++++++++++++++++++++++++++++++++
include/linux/proc_fs.h | 7 +++++++
4 files changed, 55 insertions(+)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 3faed94e4b65..ee5b6482009c 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -269,6 +269,11 @@ 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_info(dir->i_sb);
+
+ if (fs_info->pidonly == PROC_PIDONLY_ON)
+ return ERR_PTR(-ENOENT);
+
return proc_lookup_de(dir, dentry, PDE(dir));
}

@@ -325,6 +330,10 @@ 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_info(inode->i_sb);
+
+ if (fs_info->pidonly == PROC_PIDONLY_ON)
+ return 1;

return proc_readdir_de(file, ctx, PDE(inode));
}
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 91fe4896fa85..c1dbcf2b96db 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -173,6 +173,8 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid));
if (fs_info->hide_pid != HIDEPID_OFF)
seq_printf(seq, ",hidepid=%u", fs_info->hide_pid);
+ if (fs_info->pidonly != PROC_PIDONLY_OFF)
+ seq_printf(seq, ",subset=pidfs");

return 0;
}
@@ -393,12 +395,16 @@ 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_info(inode->i_sb);
struct proc_dir_entry *pde = PDE(inode);
int rv = 0;
typeof_member(struct proc_ops, proc_open) open;
typeof_member(struct proc_ops, proc_release) release;
struct pde_opener *pdeo;

+ if (fs_info->pidonly == PROC_PIDONLY_ON)
+ 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 62eae22403d2..07c309529628 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -34,16 +34,19 @@ struct proc_fs_context {
unsigned int mask;
int hidepid;
int gid;
+ int pidonly;
};

enum proc_param {
Opt_gid,
Opt_hidepid,
+ Opt_subset,
};

static const struct fs_parameter_spec proc_fs_parameters[] = {
fsparam_u32("gid", Opt_gid),
fsparam_u32("hidepid", Opt_hidepid),
+ fsparam_string("subset", Opt_subset),
{}
};

@@ -55,6 +58,29 @@ static inline int valid_hidepid(unsigned int value)
value == HIDEPID_NOT_PTRACEABLE);
}

+static int proc_parse_subset_param(struct fs_context *fc, char *value)
+{
+ struct proc_fs_context *ctx = fc->fs_private;
+
+ while (value) {
+ char *ptr = strchr(value, ',');
+
+ if (ptr != NULL)
+ *ptr++ = '\0';
+
+ if (*value != '\0') {
+ if (!strcmp(value, "pidfs")) {
+ ctx->pidonly = PROC_PIDONLY_ON;
+ } else {
+ return invalf(fc, "proc: unsupported subset option - %s\n", value);
+ }
+ }
+ value = ptr;
+ }
+
+ return 0;
+}
+
static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct proc_fs_context *ctx = fc->fs_private;
@@ -76,6 +102,11 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
ctx->hidepid = result.uint_32;
break;

+ case Opt_subset:
+ if (proc_parse_subset_param(fc, param->string) < 0)
+ return -EINVAL;
+ break;
+
default:
return -EINVAL;
}
@@ -95,6 +126,8 @@ static void proc_apply_options(struct super_block *s,
ctx->fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
if (ctx->mask & (1 << Opt_hidepid))
ctx->fs_info->hide_pid = ctx->hidepid;
+ if (ctx->mask & (1 << Opt_subset))
+ ctx->fs_info->pidonly = ctx->pidonly;
}

static int proc_fill_super(struct super_block *s, struct fs_context *fc)
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 21d19353fdc7..afd38cae2339 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -35,12 +35,19 @@ enum {
HIDEPID_NOT_PTRACEABLE = 4, /* Limit pids to only ptraceable pids */
};

+/* definitions for proc mount option pidonly */
+enum {
+ PROC_PIDONLY_OFF = 0,
+ PROC_PIDONLY_ON = 1,
+};
+
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 */
kgid_t pid_gid;
int hide_pid;
+ int pidonly;
};

static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
--
2.25.2