2020-11-06 15:19:29

by Alexey Gladkov

Subject: [PATCH v4 0/3] proc: Relax check of mount visibility

If only the dynamic part of procfs is mounted (subset=pid), then there is no
need to check if procfs is fully visible to the user in the new user namespace.

Changelog
---------
v4:
* Set SB_I_DYNAMIC only if pidonly is set.
* Add an error message if subset=pid is canceled during remount.

v3:
* Add 'const' to struct cred *mounter_cred (fix kernel test robot warning).

v2:
* cache the mounters credentials and make access to the net directories
contingent of the permissions of the mounter of procfs.

--

Alexey Gladkov (3):
proc: Relax check of mount visibility
proc: Show /proc/self/net only for CAP_NET_ADMIN
proc: Disable cancellation of subset=pid option

fs/namespace.c | 27 ++++++++++++++++-----------
fs/proc/proc_net.c | 8 ++++++++
fs/proc/root.c | 29 ++++++++++++++++++++++-------
include/linux/fs.h | 1 +
include/linux/proc_fs.h | 1 +
5 files changed, 48 insertions(+), 18 deletions(-)

--
2.25.4

2020-11-06 15:19:32

by Alexey Gladkov

Subject: [PATCH v4 3/3] proc: Disable cancellation of subset=pid option

There is no way to remount procfs mountpoint with subset=pid option
without it. This is done in order not to make visible what was hidden
since some checks occur during mount.

This patch makes this limitation explicit and demonstrates the error.

Signed-off-by: Alexey Gladkov <[email protected]>
---
fs/proc/root.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 0ab90e24d9ae..d4a91f48c430 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -145,7 +145,7 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
return 0;
}

-static void proc_apply_options(struct super_block *s,
+static int proc_apply_options(struct super_block *s,
struct fs_context *fc,
struct user_namespace *user_ns)
{
@@ -159,8 +159,11 @@ static void proc_apply_options(struct super_block *s,
if (ctx->mask & (1 << Opt_subset)) {
if (ctx->pidonly == PROC_PIDONLY_ON)
s->s_iflags |= SB_I_DYNAMIC;
+ else if (fs_info->pidonly == PROC_PIDONLY_ON)
+ return invalf(fc, "proc: subset=pid cannot be unset\n");
fs_info->pidonly = ctx->pidonly;
}
+ return 0;
}

static int proc_fill_super(struct super_block *s, struct fs_context *fc)
@@ -187,7 +190,10 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
fs_info->pid_ns = get_pid_ns(ctx->pid_ns);
fs_info->mounter_cred = get_cred(fc->cred);

- proc_apply_options(s, fc, current_user_ns());
+ ret = proc_apply_options(s, fc, current_user_ns());
+ if (ret) {
+ return ret;
+ }

/*
* procfs isn't actually a stacking filesystem; however, there is
@@ -229,8 +235,7 @@ static int proc_reconfigure(struct fs_context *fc)
put_cred(fs_info->mounter_cred);
fs_info->mounter_cred = get_cred(fc->cred);

- proc_apply_options(sb, fc, current_user_ns());
- return 0;
+ return proc_apply_options(sb, fc, current_user_ns());
}

static int proc_get_tree(struct fs_context *fc)
--
2.25.4