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>
Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 4ed6dab..2f9fa17 100644 (file)
--- 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 9c75653..0d5e68f 100644 (file)
--- 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=pid");
 
        return 0;
 }
@@ -463,6 +465,7 @@ 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;
@@ -476,6 +479,9 @@ static int proc_reg_open(struct inode *inode, struct file *file)
                return rv;
        }
 
+       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 8f23b95..baff006 100644 (file)
--- 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, "pid")) {
+                               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;
        }
@@ -94,6 +125,8 @@ static void proc_apply_options(struct proc_fs_info *fs_info,
                fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
        if (ctx->mask & (1 << Opt_hidepid))
                fs_info->hide_pid = ctx->hidepid;
+       if (ctx->mask & (1 << Opt_subset))
+               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 5bdc117..8bc31ba 100644 (file)
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -50,12 +50,19 @@ 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)