diff mbox series

[net,v2] tun: revert fix group permission check

Message ID 20250204161015.739430-1-willemdebruijn.kernel@gmail.com (mailing list archive)
State New
Delegated to: Netdev Maintainers
Headers show
Series [net,v2] tun: revert fix group permission check | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for net
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 1 maintainers not CCed: andrew+netdev@lunn.ch
netdev/build_clang success Errors and warnings before: 1 this patch: 1
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 30 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline warning Was 1 now: 1
netdev/contest success net-next-2025-02-05--00-00 (tests: 886)

Commit Message

Willem de Bruijn Feb. 4, 2025, 4:10 p.m. UTC 
From: Willem de Bruijn <willemb@google.com>

This reverts commit 3ca459eaba1bf96a8c7878de84fa8872259a01e3.

The blamed commit caused a regression when neither tun->owner nor
tun->group is set. This is intended to be allowed, but now requires
CAP_NET_ADMIN.

Discussion in the referenced thread pointed out that the original
issue that prompted this patch can be resolved in userspace.

The relaxed access control may also make a device accessible when it
previously wasn't, while existing users may depend on it to not be.

This is a clean pure git revert, except for fixing the indentation on
the gid_valid line that checkpatch correctly flagged.

Fixes: 3ca459eaba1b ("tun: fix group permission check")
Link: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/
Signed-off-by: Willem de Bruijn <willemb@google.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>
Cc: Stas Sergeev <stsp2@yandex.ru>
---
 drivers/net/tun.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)
diff mbox series

Patch

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 28624cca91f8..acf96f262488 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -574,18 +574,14 @@  static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
 	return ret;
 }
 
-static inline bool tun_capable(struct tun_struct *tun)
+static inline bool tun_not_capable(struct tun_struct *tun)
 {
 	const struct cred *cred = current_cred();
 	struct net *net = dev_net(tun->dev);
 
-	if (ns_capable(net->user_ns, CAP_NET_ADMIN))
-		return 1;
-	if (uid_valid(tun->owner) && uid_eq(cred->euid, tun->owner))
-		return 1;
-	if (gid_valid(tun->group) && in_egroup_p(tun->group))
-		return 1;
-	return 0;
+	return ((uid_valid(tun->owner) && !uid_eq(cred->euid, tun->owner)) ||
+		(gid_valid(tun->group) && !in_egroup_p(tun->group))) &&
+		!ns_capable(net->user_ns, CAP_NET_ADMIN);
 }
 
 static void tun_set_real_num_queues(struct tun_struct *tun)
@@ -2782,7 +2778,7 @@  static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		    !!(tun->flags & IFF_MULTI_QUEUE))
 			return -EINVAL;
 
-		if (!tun_capable(tun))
+		if (tun_not_capable(tun))
 			return -EPERM;
 		err = security_tun_dev_open(tun->security);
 		if (err < 0)