kernel/net/core/scm.c, branch linux-4.1.y

unix: correctly track in-flight fds in sending process user_struct

2016-03-04T15:25:48Z

[ Upstream commit 415e3d3e90ce9e18727e8843ae343eda5a58fad6 ] The commit referenced in the Fixes tag incorrectly accounted the number of in-flight fds over a unix domain socket to the original opener of the file-descriptor. This allows another process to arbitrary deplete the original file-openers resource limit for the maximum of open files. Instead the sending processes and its struct cred should be credited. To do so, we add a reference counted struct user_struct pointer to the scm_fp_list and use it to account for the number of inflight unix fds. Fixes: 712f4aad406bb1 ("unix: properly account for FDs passed over unix sockets") Reported-by: David Herrmann Cc: David Herrmann Cc: Willy Tarreau Cc: Linus Torvalds Suggested-by: Linus Torvalds Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller Signed-off-by: Sasha Levin

net, scm: fix PaX detected msg_controllen overflow in scm_detach_fds

2015-12-15T05:24:31Z

[ Upstream commit 6900317f5eff0a7070c5936e5383f589e0de7a09 ] David and HacKurx reported a following/similar size overflow triggered in a grsecurity kernel, thanks to PaX's gcc size overflow plugin: (Already fixed in later grsecurity versions by Brad and PaX Team.) [ 1002.296137] PAX: size overflow detected in function scm_detach_fds net/core/scm.c:314 cicus.202_127 min, count: 4, decl: msg_controllen; num: 0; context: msghdr; [ 1002.296145] CPU: 0 PID: 3685 Comm: scm_rights_recv Not tainted 4.2.3-grsec+ #7 [ 1002.296149] Hardware name: Apple Inc. MacBookAir5,1/Mac-66F35F19FE2A0D05, [...] [ 1002.296153] ffffffff81c27366 0000000000000000 ffffffff81c27375 ffffc90007843aa8 [ 1002.296162] ffffffff818129ba 0000000000000000 ffffffff81c27366 ffffc90007843ad8 [ 1002.296169] ffffffff8121f838 fffffffffffffffc fffffffffffffffc ffffc90007843e60 [ 1002.296176] Call Trace: [ 1002.296190] [] dump_stack+0x45/0x57 [ 1002.296200] [] report_size_overflow+0x38/0x60 [ 1002.296209] [] scm_detach_fds+0x2ce/0x300 [ 1002.296220] [] unix_stream_read_generic+0x609/0x930 [ 1002.296228] [] unix_stream_recvmsg+0x4f/0x60 [ 1002.296236] [] ? unix_set_peek_off+0x50/0x50 [ 1002.296243] [] sock_recvmsg+0x47/0x60 [ 1002.296248] [] ___sys_recvmsg+0xe2/0x1e0 [ 1002.296257] [] __sys_recvmsg+0x46/0x80 [ 1002.296263] [] SyS_recvmsg+0x2c/0x40 [ 1002.296271] [] entry_SYSCALL_64_fastpath+0x12/0x85 Further investigation showed that this can happen when an *odd* number of fds are being passed over AF_UNIX sockets. In these cases CMSG_LEN(i * sizeof(int)) and CMSG_SPACE(i * sizeof(int)), where i is the number of successfully passed fds, differ by 4 bytes due to the extra CMSG_ALIGN() padding in CMSG_SPACE() to an 8 byte boundary on 64 bit. The padding is used to align subsequent cmsg headers in the control buffer. When the control buffer passed in from the receiver side *lacks* these 4 bytes (e.g. due to buggy/wrong API usage), then msg->msg_controllen will overflow in scm_detach_fds(): int cmlen = CMSG_LEN(i * sizeof(int)); <--- cmlen w/o tail-padding err = put_user(SOL_SOCKET, &cm->cmsg_level); if (!err) err = put_user(SCM_RIGHTS, &cm->cmsg_type); if (!err) err = put_user(cmlen, &cm->cmsg_len); if (!err) { cmlen = CMSG_SPACE(i * sizeof(int)); <--- cmlen w/ 4 byte extra tail-padding msg->msg_control += cmlen; msg->msg_controllen -= cmlen; <--- iff no tail-padding space here ... } ... wrap-around F.e. it will wrap to a length of 18446744073709551612 bytes in case the receiver passed in msg->msg_controllen of 20 bytes, and the sender properly transferred 1 fd to the receiver, so that its CMSG_LEN results in 20 bytes and CMSG_SPACE in 24 bytes. In case of MSG_CMSG_COMPAT (scm_detach_fds_compat()), I haven't seen an issue in my tests as alignment seems always on 4 byte boundary. Same should be in case of native 32 bit, where we end up with 4 byte boundaries as well. In practice, passing msg->msg_controllen of 20 to recvmsg() while receiving a single fd would mean that on successful return, msg->msg_controllen is being set by the kernel to 24 bytes instead, thus more than the input buffer advertised. It could f.e. become an issue if such application later on zeroes or copies the control buffer based on the returned msg->msg_controllen elsewhere. Maximum number of fds we can send is a hard upper limit SCM_MAX_FD (253). Going over the code, it seems like msg->msg_controllen is not being read after scm_detach_fds() in scm_recv() anymore by the kernel, good! Relevant recvmsg() handler are unix_dgram_recvmsg() (unix_seqpacket_recvmsg()) and unix_stream_recvmsg(). Both return back to their recvmsg() caller, and ___sys_recvmsg() places the updated length, that is, new msg_control - old msg_control pointer into msg->msg_controllen (hence the 24 bytes seen in the example). Long time ago, Wei Yongjun fixed something related in commit 1ac70e7ad24a ("[NET]: Fix function put_cmsg() which may cause usr application memory overflow"). RFC3542, section 20.2. says: The fields shown as "XX" are possible padding, between the cmsghdr structure and the data, and between the data and the next cmsghdr structure, if required by the implementation. While sending an application may or may not include padding at the end of last ancillary data in msg_controllen and implementations must accept both as valid. On receiving a portable application must provide space for padding at the end of the last ancillary data as implementations may copy out the padding at the end of the control message buffer and include it in the received msg_controllen. When recvmsg() is called if msg_controllen is too small for all the ancillary data items including any trailing padding after the last item an implementation may set MSG_CTRUNC. Since we didn't place MSG_CTRUNC for already quite a long time, just do the same as in 1ac70e7ad24a to avoid an overflow. Btw, even man-page author got this wrong :/ See db939c9b26e9 ("cmsg.3: Fix error in SCM_RIGHTS code sample"). Some people must have copied this (?), thus it got triggered in the wild (reported several times during boot by David and HacKurx). No Fixes tag this time as pre 2002 (that is, pre history tree). Reported-by: David Sterba Reported-by: HacKurx Cc: PaX Team Cc: Emese Revfy Cc: Brad Spengler Cc: Wei Yongjun Cc: Eric Dumazet Reviewed-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

net: introduce helper macro for_each_cmsghdr

2014-12-11T03:41:55Z

Introduce helper macro for_each_cmsghdr as a wrapper of the enumerating cmsghdr from msghdr, just cleanup. Signed-off-by: Gu Zheng Signed-off-by: David S. Miller

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2013-09-07T21:35:32Z

Pull namespace changes from Eric Biederman: "This is an assorted mishmash of small cleanups, enhancements and bug fixes. The major theme is user namespace mount restrictions. nsown_capable is killed as it encourages not thinking about details that need to be considered. A very hard to hit pid namespace exiting bug was finally tracked and fixed. A couple of cleanups to the basic namespace infrastructure. Finally there is an enhancement that makes per user namespace capabilities usable as capabilities, and an enhancement that allows the per userns root to nice other processes in the user namespace" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: userns: Kill nsown_capable it makes the wrong thing easy capabilities: allow nice if we are privileged pidns: Don't have unshare(CLONE_NEWPID) imply CLONE_THREAD userns: Allow PR_CAPBSET_DROP in a user namespace. namespaces: Simplify copy_namespaces so it is clear what is going on. pidns: Fix hang in zap_pid_ns_processes by sending a potentially extra wakeup sysfs: Restrict mounting sysfs userns: Better restrictions on when proc and sysfs can be mounted vfs: Don't copy mount bind mounts of /proc//ns/mnt between namespaces kernel/nsproxy.c: Improving a snippet of code. proc: Restrict mounting the proc filesystem vfs: Lock in place mounts from more privileged users

userns: Kill nsown_capable it makes the wrong thing easy

2013-08-31T06:44:11Z

nsown_capable is a special case of ns_capable essentially for just CAP_SETUID and CAP_SETGID. For the existing users it doesn't noticably simplify things and from the suggested patches I have seen it encourages people to do the wrong thing. So remove nsown_capable. Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman"

net: Check the correct namespace when spoofing pid over SCM_RIGHTS

2013-08-27T17:52:52Z

This is a security bug. The follow-up will fix nsproxy to discourage this type of issue from happening again. Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski Reviewed-by: "Eric W. Biederman" Signed-off-by: David S. Miller

netprio_cgroup: remove task_struct parameter from sock_update_netprio()

2013-04-09T17:19:37Z

The callers always pass current to sock_update_netprio(). Signed-off-by: Li Zefan Acked-by: Neil Horman Signed-off-by: David S. Miller

cls_cgroup: remove task_struct parameter from sock_update_classid()

2013-04-09T17:19:35Z

The callers always pass current to sock_update_classid(). Signed-off-by: Li Zefan Acked-by: Neil Horman Signed-off-by: David S. Miller

scm: Stop passing struct cred

2013-04-07T22:58:55Z

Now that uids and gids are completely encapsulated in kuid_t and kgid_t we no longer need to pass struct cred which allowed us to test both the uid and the user namespace for equality. Passing struct cred potentially allows us to pass the entire group list as BSD does but I don't believe the cost of cache line misses justifies retaining code for a future potential application. Signed-off-by: "Eric W. Biederman" Signed-off-by: David S. Miller

scm: Require CAP_SYS_ADMIN over the current pidns to spoof pids.

2013-03-18T00:16:16Z

Don't allow spoofing pids over unix domain sockets in the corner cases where a user has created a user namespace but has not yet created a pid namespace. Cc: stable@vger.kernel.org Reported-by: Andy Lutomirski Signed-off-by: "Eric W. Biederman"