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Message-Id: <20170616203124.4632-1-dh.herrmann@gmail.com>
Date: Fri, 16 Jun 2017 22:31:24 +0200
From: David Herrmann <dh.herrmann@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, David Herrmann <dh.herrmann@...il.com>,
Michal Sekletar <msekleta@...hat.com>,
Simon McVittie <simon.mcvittie@...labora.co.uk>,
Tom Gundersen <teg@...m.no>
Subject: [PATCH] net: introduce SO_PEERGROUPS getsockopt
This adds the new getsockopt(2) option SO_PEERGROUPS on SOL_SOCKET to
retrieve the auxiliary groups of the remote peer. It is designed to
naturally extend SO_PEERCRED. That is, the underlying data is from the
same credentials. Regarding its syntax, it is based on SO_PEERSEC. That
is, if the provided buffer is too small, ERANGE is returned and @optlen
is updated. Otherwise, the information is copied, @optlen is set to the
actual size, and 0 is returned.
While SO_PEERCRED (and thus `struct ucred') already returns the primary
group, it lacks the auxiliary group vector. However, nearly all access
controls (including kernel side VFS and SYSVIPC, but also user-space
polkit, DBus, ...) consider the entire set of groups, rather than just
the primary group. But this is currently not possible with pure
SO_PEERCRED. Instead, user-space has to work around this and query the
system database for the auxiliary groups of a UID retrieved via
SO_PEERCRED.
Unfortunately, there is no race-free way to query the auxiliary groups
of the PID/UID retrieved via SO_PEERCRED. Hence, the current user-space
solution is to use getgrouplist(3p), which itself falls back to NSS and
whatever is configured in nsswitch.conf(3). This effectively checks
which groups we *would* assign to the user if it logged in *now*. On
normal systems it is as easy as reading /etc/group, but with NSS it can
resort to quering network databases (eg., LDAP), using IPC or network
communication.
Long story short: Whenever we want to use auxiliary groups for access
checks on IPC, we need further IPC to talk to the user/group databases,
rather than just relying on SO_PEERCRED and the incoming socket. This
is unfortunate, and might even result in dead-locks if the database
query uses the same IPC as the original request.
So far, those recursions / dead-locks have been avoided by using
primitive IPC for all crucial NSS modules. However, we want to avoid
re-inventing the wheel for each NSS module that might be involved in
user/group queries. Hence, we would preferably make DBus (and other IPC
that supports access-management based on groups) work without resorting
to the user/group database. This new SO_PEERGROUPS ioctl would allow us
to make dbus-daemon work without ever calling into NSS.
Cc: Michal Sekletar <msekleta@...hat.com>
Cc: Simon McVittie <simon.mcvittie@...labora.co.uk>
Cc: Tom Gundersen <teg@...m.no>
Signed-off-by: David Herrmann <dh.herrmann@...il.com>
---
arch/alpha/include/uapi/asm/socket.h | 2 ++
arch/frv/include/uapi/asm/socket.h | 2 ++
arch/ia64/include/uapi/asm/socket.h | 2 ++
arch/m32r/include/uapi/asm/socket.h | 2 ++
arch/mips/include/uapi/asm/socket.h | 2 ++
arch/mn10300/include/uapi/asm/socket.h | 2 ++
arch/parisc/include/uapi/asm/socket.h | 2 ++
arch/powerpc/include/uapi/asm/socket.h | 2 ++
arch/s390/include/uapi/asm/socket.h | 2 ++
arch/sparc/include/uapi/asm/socket.h | 2 ++
arch/xtensa/include/uapi/asm/socket.h | 2 ++
include/uapi/asm-generic/socket.h | 2 ++
net/core/sock.c | 33 +++++++++++++++++++++++++++++++++
13 files changed, 57 insertions(+)
diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 148d7a32754e..975c5cbf9a86 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -105,4 +105,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _UAPI_ASM_SOCKET_H */
diff --git a/arch/frv/include/uapi/asm/socket.h b/arch/frv/include/uapi/asm/socket.h
index 1ccf45657472..8e53a149b216 100644
--- a/arch/frv/include/uapi/asm/socket.h
+++ b/arch/frv/include/uapi/asm/socket.h
@@ -98,5 +98,7 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_SOCKET_H */
diff --git a/arch/ia64/include/uapi/asm/socket.h b/arch/ia64/include/uapi/asm/socket.h
index 2c3f4b48042a..d122c30429ae 100644
--- a/arch/ia64/include/uapi/asm/socket.h
+++ b/arch/ia64/include/uapi/asm/socket.h
@@ -107,4 +107,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_IA64_SOCKET_H */
diff --git a/arch/m32r/include/uapi/asm/socket.h b/arch/m32r/include/uapi/asm/socket.h
index ae6548d29a18..7e689cc14668 100644
--- a/arch/m32r/include/uapi/asm/socket.h
+++ b/arch/m32r/include/uapi/asm/socket.h
@@ -98,4 +98,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_M32R_SOCKET_H */
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 3418ec9c1c50..5c0947d063cc 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -116,4 +116,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _UAPI_ASM_SOCKET_H */
diff --git a/arch/mn10300/include/uapi/asm/socket.h b/arch/mn10300/include/uapi/asm/socket.h
index 4526e92301a6..219f516eb6ad 100644
--- a/arch/mn10300/include/uapi/asm/socket.h
+++ b/arch/mn10300/include/uapi/asm/socket.h
@@ -98,4 +98,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_SOCKET_H */
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index 514701840bd9..2dd2c132047e 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -97,4 +97,6 @@
#define SO_COOKIE 0x4032
+#define SO_PEERGROUPS 0x4033
+
#endif /* _UAPI_ASM_SOCKET_H */
diff --git a/arch/powerpc/include/uapi/asm/socket.h b/arch/powerpc/include/uapi/asm/socket.h
index 58e2ec0310fc..2ce8c4503b1c 100644
--- a/arch/powerpc/include/uapi/asm/socket.h
+++ b/arch/powerpc/include/uapi/asm/socket.h
@@ -105,4 +105,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_POWERPC_SOCKET_H */
diff --git a/arch/s390/include/uapi/asm/socket.h b/arch/s390/include/uapi/asm/socket.h
index e8e5ecf673fd..90f0899a1064 100644
--- a/arch/s390/include/uapi/asm/socket.h
+++ b/arch/s390/include/uapi/asm/socket.h
@@ -104,4 +104,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _ASM_SOCKET_H */
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 3f4ad19d9ec7..5dd96465bc5e 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -94,6 +94,8 @@
#define SO_COOKIE 0x003b
+#define SO_PEERGROUPS 0x003c
+
/* Security levels - as per NRL IPv6 - don't actually do anything */
#define SO_SECURITY_AUTHENTICATION 0x5001
#define SO_SECURITY_ENCRYPTION_TRANSPORT 0x5002
diff --git a/arch/xtensa/include/uapi/asm/socket.h b/arch/xtensa/include/uapi/asm/socket.h
index 1eb6d2fe70d3..e6df5066b9e3 100644
--- a/arch/xtensa/include/uapi/asm/socket.h
+++ b/arch/xtensa/include/uapi/asm/socket.h
@@ -109,4 +109,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* _XTENSA_SOCKET_H */
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 2b488565599d..79634c00611b 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -100,4 +100,6 @@
#define SO_COOKIE 57
+#define SO_PEERGROUPS 58
+
#endif /* __ASM_GENERIC_SOCKET_H */
diff --git a/net/core/sock.c b/net/core/sock.c
index 727f924b7f91..1987bf13d755 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1074,6 +1074,18 @@ static void cred_to_ucred(struct pid *pid, const struct cred *cred,
}
}
+static int groups_to_user(gid_t __user *dst, const struct group_info *src)
+{
+ struct user_namespace *user_ns = current_user_ns();
+ int i;
+
+ for (i = 0; i < src->ngroups; i++)
+ if (put_user(from_kgid_munged(user_ns, src->gid[i]), dst + i))
+ return -EFAULT;
+
+ return 0;
+}
+
int sock_getsockopt(struct socket *sock, int level, int optname,
char __user *optval, int __user *optlen)
{
@@ -1227,6 +1239,27 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
goto lenout;
}
+ case SO_PEERGROUPS:
+ {
+ int ret, n;
+
+ if (!sk->sk_peer_cred)
+ return -ENODATA;
+
+ n = sk->sk_peer_cred->group_info->ngroups;
+ if (len < n * sizeof(gid_t)) {
+ len = n * sizeof(gid_t);
+ return put_user(len, optlen) ? -EFAULT : -ERANGE;
+ }
+ len = n * sizeof(gid_t);
+
+ ret = groups_to_user((gid_t __user *)optval,
+ sk->sk_peer_cred->group_info);
+ if (ret)
+ return ret;
+ goto lenout;
+ }
+
case SO_PEERNAME:
{
char address[128];
--
2.13.1
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