[PATCH RESEND v9 8/8] proc: use human-readable values for hidehid

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

The hidepid parameter values are becoming more and more and it becomes
difficult to remember what each new magic number means.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
Documentation/filesystems/proc.txt | 52 +++++++++++++++---------------
fs/proc/inode.c | 13 +++++++-
fs/proc/root.c | 36 +++++++++++++++++++--
3 files changed, 71 insertions(+), 30 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 4741fd092f36..27830a93464b 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -2025,28 +2025,28 @@ The following mount options are supported:
gid= Set the group authorized to learn processes information.
subset= Show only the specified subset of procfs.

-hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
-(default).
-
-hidepid=1 means users may not access any /proc/<pid>/ directories but their
-own. Sensitive files like cmdline, sched*, status are now protected against
-other users. This makes it impossible to learn whether any user runs
-specific program (given the program doesn't reveal itself by its behaviour).
-As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
-poorly written programs passing sensitive information via program arguments are
-now protected against local eavesdroppers.
-
-hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
-users. It doesn't mean that it hides a fact whether a process with a specific
-pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
-but it hides process' uid and gid, which may be learned by stat()'ing
-/proc/<pid>/ otherwise. It greatly complicates an intruder's task of gathering
-information about running processes, whether some daemon runs with elevated
-privileges, whether other user runs some sensitive program, whether other users
-run any program at all, etc.
-
-hidepid=4 means that procfs should only contain /proc/<pid>/ directories
-that the caller can ptrace.
+hidepid=off or hidepid=0 means classic mode - everybody may access all
+/proc/<pid>/ directories (default).
+
+hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
+directories but their own. Sensitive files like cmdline, sched*, status are now
+protected against other users. This makes it impossible to learn whether any
+user runs specific program (given the program doesn't reveal itself by its
+behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
+other users, poorly written programs passing sensitive information via program
+arguments are now protected against local eavesdroppers.
+
+hidepid=invisible or hidepid=2 means hidepid=noaccess plus all /proc/<pid>/ will
+be fully invisible to other users. It doesn't mean that it hides a fact whether
+a process with a specific pid value exists (it can be learned by other means,
+e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned
+by stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task
+of gathering information about running processes, whether some daemon runs with
+elevated privileges, whether other user runs some sensitive program, whether
+other users run any program at all, etc.
+
+hidepid=ptraceable or hidepid=4 means that procfs should only contain
+/proc/<pid>/ directories that the caller can ptrace.

gid= defines a group authorized to learn processes information otherwise
prohibited by hidepid=. If you use some daemon like identd which needs to learn
@@ -2093,8 +2093,8 @@ creates a new procfs instance. Mount options affect own procfs instance.
It means that it became possible to have several procfs instances
displaying tasks with different filtering options in one pid namespace.

-# mount -o hidepid=2 -t proc proc /proc
-# mount -o hidepid=1 -t proc proc /tmp/proc
+# mount -o hidepid=invisible -t proc proc /proc
+# mount -o hidepid=noaccess -t proc proc /tmp/proc
# grep ^proc /proc/mounts
-proc /proc proc rw,relatime,hidepid=2 0 0
-proc /tmp/proc proc rw,relatime,hidepid=1 0 0
+proc /proc proc rw,relatime,hidepid=invisible 0 0
+proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index c1dbcf2b96db..a462fd111719 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -165,6 +165,17 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock
deactivate_super(old_sb);
}

+static inline const char *hidepid2str(int v)
+{
+ switch (v) {
+ case HIDEPID_OFF: return "off";
+ case HIDEPID_NO_ACCESS: return "noaccess";
+ case HIDEPID_INVISIBLE: return "invisible";
+ case HIDEPID_NOT_PTRACEABLE: return "ptraceable";
+ }
+ BUG();
+}
+
static int proc_show_options(struct seq_file *seq, struct dentry *root)
{
struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
@@ -172,7 +183,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID))
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);
+ seq_printf(seq, ",hidepid=%s", hidepid2str(fs_info->hide_pid));
if (fs_info->pidonly != PROC_PIDONLY_OFF)
seq_printf(seq, ",subset=pidfs");

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 07c309529628..42f3ee05c584 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -45,7 +45,7 @@ enum proc_param {

static const struct fs_parameter_spec proc_fs_parameters[] = {
fsparam_u32("gid", Opt_gid),
- fsparam_u32("hidepid", Opt_hidepid),
+ fsparam_string("hidepid", Opt_hidepid),
fsparam_string("subset", Opt_subset),
{}
};
@@ -58,6 +58,35 @@ static inline int valid_hidepid(unsigned int value)
value == HIDEPID_NOT_PTRACEABLE);
}

+static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param)
+{
+ struct proc_fs_context *ctx = fc->fs_private;
+ struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid);
+ struct fs_parse_result result;
+ int base = (unsigned long)hidepid_u32_spec.data;
+
+ if (param->type != fs_value_is_string)
+ return invalf(fc, "proc: unexpected type of hidepid value\n");
+
+ if (!kstrtouint(param->string, base, &result.uint_32)) {
+ ctx->hidepid = result.uint_32;
+ return 0;
+ }
+
+ if (!strcmp(param->string, "off"))
+ ctx->hidepid = HIDEPID_OFF;
+ else if (!strcmp(param->string, "noaccess"))
+ ctx->hidepid = HIDEPID_NO_ACCESS;
+ else if (!strcmp(param->string, "invisible"))
+ ctx->hidepid = HIDEPID_INVISIBLE;
+ else if (!strcmp(param->string, "ptraceable"))
+ ctx->hidepid = HIDEPID_NOT_PTRACEABLE;
+ else
+ return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string);
+
+ return 0;
+}
+
static int proc_parse_subset_param(struct fs_context *fc, char *value)
{
struct proc_fs_context *ctx = fc->fs_private;
@@ -97,9 +126,10 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
break;

case Opt_hidepid:
- if (!valid_hidepid(result.uint_32))
+ if (proc_parse_hidepid_param(fc, param))
+ return -EINVAL;
+ if (!valid_hidepid(ctx->hidepid))
return invalf(fc, "proc: unknown value of hidepid.\n");
- ctx->hidepid = result.uint_32;
break;

case Opt_subset:
--
2.25.2