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From: Richard Weinberger <richard@nod.at>
To: alx@kernel.org, serge@hallyn.com, christian@brauner.io,
	ipedrosa@redhat.com, gscrivan@redhat.com,
	andreas.gruenbacher@gmail.com
Cc: acl-devel@nongnu.org, linux-man@vger.kernel.org,
	linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	ebiederm@xmission.com, Richard Weinberger <richard@nod.at>
Subject: [PATCH 1/3] man: Document pitfall with negative permissions and user namespaces
Date: Tue, 29 Aug 2023 22:58:31 +0200	[thread overview]
Message-ID: <20230829205833.14873-2-richard@nod.at> (raw)
In-Reply-To: <20230829205833.14873-1-richard@nod.at>

It is little known that user namespaces and some helpers
can be used to bypass negative permissions.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
This patch applies to the acl software project.
---
 man/man5/acl.5 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/man/man5/acl.5 b/man/man5/acl.5
index 0db86b325617..2ed144742e37 100644
--- a/man/man5/acl.5
+++ b/man/man5/acl.5
@@ -495,5 +495,20 @@ These non-portable extensions are available on Linux systems.
 .Xr acl_from_mode 3 ,
 .Xr acl_get_perm 3 ,
 .Xr acl_to_any_text 3
+.Sh NOTES
+.Ss Negative permissions and Linux user namespaces
+While it is technically feasible to establish negative permissions through
+ACLs, such an approach is widely regarded as a suboptimal practice.
+Furthermore, the utilization of Linux user namespaces introduces the
+potential to circumvent specific negative permissions.  This issue stems
+from the fact that privileged helpers, such as
+.Xr newuidmap 1 ,
+enable unprivileged users to create user namespaces with subordinate user and
+group IDs. As a consequence, users can drop group memberships, resulting
+in a situation where negative permissions based on group membership no longer
+apply.
+For more details, please refer to the
+.Xr user_namespaces 7
+documentation.
 .Sh AUTHOR
 Andreas Gruenbacher, <andreas.gruenbacher@gmail.com>
-- 
2.26.2


  reply	other threads:[~2023-08-29 20:59 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-29 20:58 [PATCH 0/3] Document impact of user namespaces and negative permissions Richard Weinberger
2023-08-29 20:58 ` Richard Weinberger [this message]
2023-08-30  8:19   ` [PATCH 1/3] man: Document pitfall with negative permissions and user namespaces Christian Brauner
2023-08-29 20:58 ` [PATCH 2/3] user_namespaces.7: " Richard Weinberger
2023-08-29 21:32   ` Alejandro Colomar
2023-08-29 21:38     ` Alejandro Colomar
2023-08-29 21:40       ` Richard Weinberger
2023-08-29 21:39     ` Richard Weinberger
2023-08-29 21:40       ` Alejandro Colomar
2023-08-30  9:26     ` Alejandro Colomar
2023-08-30  8:18   ` Christian Brauner
2023-08-29 20:58 ` [PATCH 3/3] man: " Richard Weinberger
2023-08-30  8:19   ` Christian Brauner
2023-08-29 21:26 ` [PATCH 0/3] Document impact of user namespaces and negative permissions Alejandro Colomar
2023-08-29 21:32   ` Richard Weinberger
2023-09-13 14:35     ` Alejandro Colomar

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