Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Djalal Harouni]

On Fri, Nov 10, 2017 at 3:38 AM, Andy Lutomirski  wrote:
> On Thu, Nov 9, 2017 at 8:14 AM, Djalal Harouni  wrote:
>> This patch introduces the new 'pids' mount option, as it was discussed
>> and suggested by Andy Lutomirski [1].
>>
>> * If 'pids=' is passed without 'newinstance' then it has no effect.
>
> Would it be safer this were an error instead?

Hm, I tend to say that you are right, but I also keep your comment
when you said that "newinstance" should be the default later and users
won't have to explicitly pass it. What you think ?

-- 
tixxdz

Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Djalal Harouni]

On Fri, Nov 10, 2017 at 3:38 AM, Andy Lutomirski  wrote:
> On Thu, Nov 9, 2017 at 8:14 AM, Djalal Harouni  wrote:
>> This patch introduces the new 'pids' mount option, as it was discussed
>> and suggested by Andy Lutomirski [1].
>>
>> * If 'pids=' is passed without 'newinstance' then it has no effect.
>
> Would it be safer this were an error instead?

Hm, I tend to say that you are right, but I also keep your comment
when you said that "newinstance" should be the default later and users
won't have to explicitly pass it. What you think ?

-- 
tixxdz

Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[James Morris]

On Thu, 9 Nov 2017, Djalal Harouni wrote:

> This patch introduces the new 'pids' mount option, as it was discussed
> and suggested by Andy Lutomirski [1].
> 
> * If 'pids=' is passed without 'newinstance' then it has no effect.
> 
> * If 'newinstance,pids=all' then all processes will be shown in proc.
> 
> * If 'newinstance,pids=ptraceable' then only ptraceable processes will be
> shown.
> 
> * 'pids=' takes precendence over 'hidepid=' since 'hidepid=' can be
>   ignored if "gid=" was set and caller has the "gid=" set in its groups.
>   We want to guarantee that LSM have a security path there that can not
>   be disabled with "gid=".
> 
> This allows to support lightweight sandboxes in Embedded Linux.
> 
> Later Yama LSM can be updated to check that processes are able only
> able to see their children inside /proc/, allowing to support more tight
> cases.
> 
> [1] https://lkml.org/lkml/2017/4/26/646
> 
> Cc: Kees Cook 
> Cc: Greg Kroah-Hartman 
> Suggested-by: Andy Lutomirski 
> Signed-off-by: Alexey Gladkov 
> Signed-off-by: Djalal Harouni 


Reviewed-by: James Morris 


-- 
James Morris

Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[James Morris]

On Thu, 9 Nov 2017, Djalal Harouni wrote:

> This patch introduces the new 'pids' mount option, as it was discussed
> and suggested by Andy Lutomirski [1].
> 
> * If 'pids=' is passed without 'newinstance' then it has no effect.
> 
> * If 'newinstance,pids=all' then all processes will be shown in proc.
> 
> * If 'newinstance,pids=ptraceable' then only ptraceable processes will be
> shown.
> 
> * 'pids=' takes precendence over 'hidepid=' since 'hidepid=' can be
>   ignored if "gid=" was set and caller has the "gid=" set in its groups.
>   We want to guarantee that LSM have a security path there that can not
>   be disabled with "gid=".
> 
> This allows to support lightweight sandboxes in Embedded Linux.
> 
> Later Yama LSM can be updated to check that processes are able only
> able to see their children inside /proc/, allowing to support more tight
> cases.
> 
> [1] https://lkml.org/lkml/2017/4/26/646
> 
> Cc: Kees Cook 
> Cc: Greg Kroah-Hartman 
> Suggested-by: Andy Lutomirski 
> Signed-off-by: Alexey Gladkov 
> Signed-off-by: Djalal Harouni 


Reviewed-by: James Morris 


-- 
James Morris

Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Andy Lutomirski]

On Thu, Nov 9, 2017 at 8:14 AM, Djalal Harouni  wrote:
> This patch introduces the new 'pids' mount option, as it was discussed
> and suggested by Andy Lutomirski [1].
>
> * If 'pids=' is passed without 'newinstance' then it has no effect.

Would it be safer this were an error instead?

Re: [PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Andy Lutomirski]

On Thu, Nov 9, 2017 at 8:14 AM, Djalal Harouni  wrote:
> This patch introduces the new 'pids' mount option, as it was discussed
> and suggested by Andy Lutomirski [1].
>
> * If 'pids=' is passed without 'newinstance' then it has no effect.

Would it be safer this were an error instead?

[PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Djalal Harouni]

This patch introduces the new 'pids' mount option, as it was discussed
and suggested by Andy Lutomirski [1].

* If 'pids=' is passed without 'newinstance' then it has no effect.

* If 'newinstance,pids=all' then all processes will be shown in proc.

* If 'newinstance,pids=ptraceable' then only ptraceable processes will be
shown.

* 'pids=' takes precendence over 'hidepid=' since 'hidepid=' can be
  ignored if "gid=" was set and caller has the "gid=" set in its groups.
  We want to guarantee that LSM have a security path there that can not
  be disabled with "gid=".

This allows to support lightweight sandboxes in Embedded Linux.

Later Yama LSM can be updated to check that processes are able only
able to see their children inside /proc/, allowing to support more tight
cases.

[1] https://lkml.org/lkml/2017/4/26/646

Cc: Kees Cook 
Cc: Greg Kroah-Hartman 
Suggested-by: Andy Lutomirski 
Signed-off-by: Alexey Gladkov 
Signed-off-by: Djalal Harouni 
---
 fs/proc/base.c  | 36 +---
 fs/proc/inode.c |  6 +-
 fs/proc/root.c  | 20 ++--
 include/linux/proc_fs.h | 30 ++
 4 files changed, 82 insertions(+), 10 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 54b527c..88b92bc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -686,13 +686,24 @@ static bool has_pid_permissions(struct proc_fs_info 
*fs_info,
 struct task_struct *task,
 int hide_pid_min)
 {
-   int hide_pid = proc_fs_hide_pid(fs_info);
-   kgid_t gid = proc_fs_pid_gid(fs_info);
+   int pids = proc_fs_pids(fs_info);
+
+   /*
+* If 'pids=all' or if it was not set then lets fallback
+* to 'hidepid' and 'gid', if those are not enforced too, then
+* ptrace checks are skipped. Otherwise ptrace permission is
+* required for all other cases.
+*/
+   if (pids == PIDS_ALL) {
+   int hide_pid = proc_fs_hide_pid(fs_info);
+   kgid_t gid = proc_fs_pid_gid(fs_info);
+
+   if (hide_pid < hide_pid_min)
+   return true;
 
-   if (hide_pid < hide_pid_min)
-   return true;
-   if (in_group_p(gid))
-   return true;
+   if (in_group_p(gid))
+   return true;
+   }
return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
 }
 
@@ -701,6 +712,7 @@ static int proc_pid_permission(struct inode *inode, int 
mask)
 {
struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
int hide_pid = proc_fs_hide_pid(fs_info);
+   int pids = proc_fs_pids(fs_info);
struct task_struct *task;
bool has_perms;
 
@@ -711,7 +723,8 @@ static int proc_pid_permission(struct inode *inode, int 
mask)
put_task_struct(task);
 
if (!has_perms) {
-   if (hide_pid == HIDEPID_INVISIBLE) {
+   if (pids == PIDS_PTRACEABLE ||
+   hide_pid == HIDEPID_INVISIBLE) {
/*
 * Let's make getdents(), stat(), and open()
 * consistent with each other.  If a process
@@ -3140,6 +3153,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
unsigned tgid;
struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
struct pid_namespace *ns = fs_info->pid_ns;
+   int pids = proc_fs_pids(fs_info);
 
tgid = name_to_int(>d_name);
if (tgid == ~0U)
@@ -3153,7 +3167,15 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
if (!task)
goto out;
 
+   /* Limit procfs to only ptraceable tasks */
+   if (pids != PIDS_ALL) {
+   cond_resched();
+   if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+   goto out_put_task;
+   }
+
result = proc_pid_instantiate(dir, dentry, task, NULL);
+out_put_task:
put_task_struct(task);
 out:
return ERR_PTR(result);
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index faec32a..2707d5f 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -108,8 +108,12 @@ static int proc_show_options(struct seq_file *seq, struct 
dentry *root)
int hide_pid = proc_fs_hide_pid(fs_info);
kgid_t pid_gid = proc_fs_pid_gid(fs_info);
 
-   if (proc_fs_newinstance(fs_info))
+   if (proc_fs_newinstance(fs_info)) {
+   int pids = proc_fs_pids(fs_info);
+
seq_printf(seq, ",newinstance");
+   seq_printf(seq, ",pids=%s", pids == PIDS_ALL ? "all" : 
"ptraceable");
+   }
 
if (!gid_eq(pid_gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u", 
from_kgid_munged(current_user_ns(),pid_gid));
diff --git a/fs/proc/root.c 

[PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option

[Djalal Harouni]

This patch introduces the new 'pids' mount option, as it was discussed
and suggested by Andy Lutomirski [1].

* If 'pids=' is passed without 'newinstance' then it has no effect.

* If 'newinstance,pids=all' then all processes will be shown in proc.

* If 'newinstance,pids=ptraceable' then only ptraceable processes will be
shown.

* 'pids=' takes precendence over 'hidepid=' since 'hidepid=' can be
  ignored if "gid=" was set and caller has the "gid=" set in its groups.
  We want to guarantee that LSM have a security path there that can not
  be disabled with "gid=".

This allows to support lightweight sandboxes in Embedded Linux.

Later Yama LSM can be updated to check that processes are able only
able to see their children inside /proc/, allowing to support more tight
cases.

[1] https://lkml.org/lkml/2017/4/26/646

Cc: Kees Cook 
Cc: Greg Kroah-Hartman 
Suggested-by: Andy Lutomirski 
Signed-off-by: Alexey Gladkov 
Signed-off-by: Djalal Harouni 
---
 fs/proc/base.c  | 36 +---
 fs/proc/inode.c |  6 +-
 fs/proc/root.c  | 20 ++--
 include/linux/proc_fs.h | 30 ++
 4 files changed, 82 insertions(+), 10 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 54b527c..88b92bc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -686,13 +686,24 @@ static bool has_pid_permissions(struct proc_fs_info 
*fs_info,
 struct task_struct *task,
 int hide_pid_min)
 {
-   int hide_pid = proc_fs_hide_pid(fs_info);
-   kgid_t gid = proc_fs_pid_gid(fs_info);
+   int pids = proc_fs_pids(fs_info);
+
+   /*
+* If 'pids=all' or if it was not set then lets fallback
+* to 'hidepid' and 'gid', if those are not enforced too, then
+* ptrace checks are skipped. Otherwise ptrace permission is
+* required for all other cases.
+*/
+   if (pids == PIDS_ALL) {
+   int hide_pid = proc_fs_hide_pid(fs_info);
+   kgid_t gid = proc_fs_pid_gid(fs_info);
+
+   if (hide_pid < hide_pid_min)
+   return true;
 
-   if (hide_pid < hide_pid_min)
-   return true;
-   if (in_group_p(gid))
-   return true;
+   if (in_group_p(gid))
+   return true;
+   }
return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
 }
 
@@ -701,6 +712,7 @@ static int proc_pid_permission(struct inode *inode, int 
mask)
 {
struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
int hide_pid = proc_fs_hide_pid(fs_info);
+   int pids = proc_fs_pids(fs_info);
struct task_struct *task;
bool has_perms;
 
@@ -711,7 +723,8 @@ static int proc_pid_permission(struct inode *inode, int 
mask)
put_task_struct(task);
 
if (!has_perms) {
-   if (hide_pid == HIDEPID_INVISIBLE) {
+   if (pids == PIDS_PTRACEABLE ||
+   hide_pid == HIDEPID_INVISIBLE) {
/*
 * Let's make getdents(), stat(), and open()
 * consistent with each other.  If a process
@@ -3140,6 +3153,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
unsigned tgid;
struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
struct pid_namespace *ns = fs_info->pid_ns;
+   int pids = proc_fs_pids(fs_info);
 
tgid = name_to_int(>d_name);
if (tgid == ~0U)
@@ -3153,7 +3167,15 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
if (!task)
goto out;
 
+   /* Limit procfs to only ptraceable tasks */
+   if (pids != PIDS_ALL) {
+   cond_resched();
+   if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+   goto out_put_task;
+   }
+
result = proc_pid_instantiate(dir, dentry, task, NULL);
+out_put_task:
put_task_struct(task);
 out:
return ERR_PTR(result);
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index faec32a..2707d5f 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -108,8 +108,12 @@ static int proc_show_options(struct seq_file *seq, struct 
dentry *root)
int hide_pid = proc_fs_hide_pid(fs_info);
kgid_t pid_gid = proc_fs_pid_gid(fs_info);
 
-   if (proc_fs_newinstance(fs_info))
+   if (proc_fs_newinstance(fs_info)) {
+   int pids = proc_fs_pids(fs_info);
+
seq_printf(seq, ",newinstance");
+   seq_printf(seq, ",pids=%s", pids == PIDS_ALL ? "all" : 
"ptraceable");
+   }
 
if (!gid_eq(pid_gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u", 
from_kgid_munged(current_user_ns(),pid_gid));
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 33ab965..5cdff69 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -28,13 +28,14 @@