[PATCH v2 1/2] openat2: reject RESOLVE_BENEATH|RESOLVE_IN_ROOT

From: Aleksa Sarai <cyphar@cyphar.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>, Shuah Khan <shuah@kernel.org>
Cc: containers@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH v2 1/2] openat2: reject RESOLVE_BENEATH|RESOLVE_IN_ROOT
Date: Wed, 28 Oct 2020 10:50:43 +1100	[thread overview]
Message-ID: <20201027235044.5240-2-cyphar@cyphar.com> (raw)
In-Reply-To: <20201027235044.5240-1-cyphar@cyphar.com>

This was an oversight in the original implementation, as it makes no
sense to specify both scoping flags to the same openat2(2) invocation
(before this patch, the result of such an invocation was equivalent to
RESOLVE_IN_ROOT being ignored).

This is a userspace-visible ABI change, but the only user of openat2(2)
at the moment is LXC which doesn't specify both flags and so no
userspace programs will break as a result.

Cc: <stable@vger.kernel.org> # v5.6+
Fixes: fddb5d430ad9 ("open: introduce openat2(2) syscall")
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 fs/open.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/open.c b/fs/open.c
index 9af548fb841b..4d7537ae59df 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1010,6 +1010,10 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op)
 	if (how->resolve & ~VALID_RESOLVE_FLAGS)
 		return -EINVAL;
 
+	/* Scoping flags are mutually exclusive. */
+	if ((how->resolve & RESOLVE_BENEATH) && (how->resolve & RESOLVE_IN_ROOT))
+		return -EINVAL;
+
 	/* Deal with the mode. */
 	if (WILL_CREATE(flags)) {
 		if (how->mode & ~S_IALLUGO)
-- 
2.29.0

_______________________________________________
Containers mailing list
Containers@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/containers
