kernel/git/stable/linux.git/net/l2tp, branch linux-4.17.y

l2tp: use sk_dst_check() to avoid race on sk->sk_dst_cache

2018-08-22T05:44:51+00:00

[ Upstream commit 6d37fa49da1e8db8fb1995be22ac837ca41ac8a8 ] In l2tp code, if it is a L2TP_UDP_ENCAP tunnel, tunnel->sk points to a UDP socket. User could call sendmsg() on both this tunnel and the UDP socket itself concurrently. As l2tp_xmit_skb() holds socket lock and call __sk_dst_check() to refresh sk->sk_dst_cache, while udpv6_sendmsg() is lockless and call sk_dst_check() to refresh sk->sk_dst_cache, there could be a race and cause the dst cache to be freed multiple times. So we fix l2tp side code to always call sk_dst_check() to garantee xchg() is called when refreshing sk->sk_dst_cache to avoid race conditions. Syzkaller reported stack trace: BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] BUG: KASAN: use-after-free in atomic_fetch_add_unless include/linux/atomic.h:575 [inline] BUG: KASAN: use-after-free in atomic_add_unless include/linux/atomic.h:597 [inline] BUG: KASAN: use-after-free in dst_hold_safe include/net/dst.h:308 [inline] BUG: KASAN: use-after-free in ip6_hold_safe+0xe6/0x670 net/ipv6/route.c:1029 Read of size 4 at addr ffff8801aea9a880 by task syz-executor129/4829 CPU: 0 PID: 4829 Comm: syz-executor129 Not tainted 4.18.0-rc7-next-20180802+ #30 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113 print_address_description+0x6c/0x20b mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412 check_memory_region_inline mm/kasan/kasan.c:260 [inline] check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267 kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272 atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] atomic_fetch_add_unless include/linux/atomic.h:575 [inline] atomic_add_unless include/linux/atomic.h:597 [inline] dst_hold_safe include/net/dst.h:308 [inline] ip6_hold_safe+0xe6/0x670 net/ipv6/route.c:1029 rt6_get_pcpu_route net/ipv6/route.c:1249 [inline] ip6_pol_route+0x354/0xd20 net/ipv6/route.c:1922 ip6_pol_route_output+0x54/0x70 net/ipv6/route.c:2098 fib6_rule_lookup+0x283/0x890 net/ipv6/fib6_rules.c:122 ip6_route_output_flags+0x2c5/0x350 net/ipv6/route.c:2126 ip6_dst_lookup_tail+0x1278/0x1da0 net/ipv6/ip6_output.c:978 ip6_dst_lookup_flow+0xc8/0x270 net/ipv6/ip6_output.c:1079 ip6_sk_dst_lookup_flow+0x5ed/0xc50 net/ipv6/ip6_output.c:1117 udpv6_sendmsg+0x2163/0x36b0 net/ipv6/udp.c:1354 inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798 sock_sendmsg_nosec net/socket.c:622 [inline] sock_sendmsg+0xd5/0x120 net/socket.c:632 ___sys_sendmsg+0x51d/0x930 net/socket.c:2115 __sys_sendmmsg+0x240/0x6f0 net/socket.c:2210 __do_sys_sendmmsg net/socket.c:2239 [inline] __se_sys_sendmmsg net/socket.c:2236 [inline] __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2236 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x446a29 Code: e8 ac b8 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f4de5532db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00000000006dcc38 RCX: 0000000000446a29 RDX: 00000000000000b8 RSI: 0000000020001b00 RDI: 0000000000000003 RBP: 00000000006dcc30 R08: 00007f4de5533700 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc3c R13: 00007ffe2b830fdf R14: 00007f4de55339c0 R15: 0000000000000001 Fixes: 71b1391a4128 ("l2tp: ensure sk->dst is still valid") Reported-by: syzbot+05f840f3b04f211bad55@syzkaller.appspotmail.com Signed-off-by: Wei Wang Signed-off-by: Martin KaFai Lau Cc: Guillaume Nault Cc: David Ahern Cc: Cong Wang Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

l2tp: fix refcount leakage on PPPoL2TP sockets

2018-06-11T20:43:18+00:00

[ Upstream commit 3d609342cc04129ff7568e19316ce3d7451a27e8 ] Commit d02ba2a6110c ("l2tp: fix race in pppol2tp_release with session object destroy") tried to fix a race condition where a PPPoL2TP socket would disappear while the L2TP session was still using it. However, it missed the root issue which is that an L2TP session may accept to be reconnected if its associated socket has entered the release process. The tentative fix makes the session hold the socket it is connected to. That saves the kernel from crashing, but introduces refcount leakage, preventing the socket from completing the release process. Once stalled, everything the socket depends on can't be released anymore, including the L2TP session and the l2tp_ppp module. The root issue is that, when releasing a connected PPPoL2TP socket, the session's ->sk pointer (RCU-protected) is reset to NULL and we have to wait for a grace period before destroying the socket. The socket drops the session in its ->sk_destruct callback function, so the session will exist until the last reference on the socket is dropped. Therefore, there is a time frame where pppol2tp_connect() may accept reconnecting a session, as it only checks ->sk to figure out if the session is connected. This time frame is shortened by the fact that pppol2tp_release() calls l2tp_session_delete(), making the session unreachable before resetting ->sk. However, pppol2tp_connect() may grab the session before it gets unhashed by l2tp_session_delete(), but it may test ->sk after the later got reset. The race is not so hard to trigger and syzbot found a pretty reliable reproducer: https://syzkaller.appspot.com/bug?id=418578d2a4389074524e04d641eacb091961b2cf Before d02ba2a6110c, another race could let pppol2tp_release() overwrite the ->__sk pointer of an L2TP session, thus tricking pppol2tp_put_sk() into calling sock_put() on a socket that is different than the one for which pppol2tp_release() was originally called. To get there, we had to trigger the race described above, therefore having one PPPoL2TP socket being released, while the session it is connected to is reconnecting to a different PPPoL2TP socket. When releasing this new socket fast enough, pppol2tp_release() overwrites the session's ->__sk pointer with the address of the new socket, before the first pppol2tp_put_sk() call gets scheduled. Then the pppol2tp_put_sk() call invoked by the original socket will sock_put() the new socket, potentially dropping its last reference. When the second pppol2tp_put_sk() finally runs, its socket has already been freed. With d02ba2a6110c, the session takes a reference on both sockets. Furthermore, the session's ->sk pointer is reset in the pppol2tp_session_close() callback function rather than in pppol2tp_release(). Therefore, ->__sk can't be overwritten and pppol2tp_put_sk() is called only once (l2tp_session_delete() will only run pppol2tp_session_close() once, to protect the session against concurrent deletion requests). Now pppol2tp_put_sk() will properly sock_put() the original socket, but the new socket will remain, as l2tp_session_delete() prevented the release process from completing. Here, we don't depend on the ->__sk race to trigger the bug. Getting into the pppol2tp_connect() race is enough to leak the reference, no matter when new socket is released. So it all boils down to pppol2tp_connect() failing to realise that the session has already been connected. This patch drops the unneeded extra reference counting (mostly reverting d02ba2a6110c) and checks that neither ->sk nor ->__sk is set before allowing a session to be connected. Fixes: d02ba2a6110c ("l2tp: fix race in pppol2tp_release with session object destroy") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

l2tp: check sockaddr length in pppol2tp_connect()

2018-04-24T01:10:43+00:00

Check sockaddr_len before dereferencing sp->sa_protocol, to ensure that it actually points to valid data. Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Reported-by: syzbot+a70ac890b23b1bf29f5c@syzkaller.appspotmail.com Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: fix {pppol2tp, l2tp_dfs}_seq_stop() in case of seq_file overflow

2018-04-22T18:46:35+00:00

Commit 0e0c3fee3a59 ("l2tp: hold reference on tunnels printed in pppol2tp proc file") assumed that if pppol2tp_seq_stop() was called with non-NULL private data (the 'v' pointer), then pppol2tp_seq_start() would not be called again. It turns out that this isn't guaranteed, and overflowing the seq_file's buffer in pppol2tp_seq_show() is a way to get into this situation. Therefore, pppol2tp_seq_stop() needs to reset pd->tunnel, so that pppol2tp_seq_start() won't drop a reference again if it gets called. We also have to clear pd->session, because the rest of the code expects a non-NULL tunnel when pd->session is set. The l2tp_debugfs module has the same issue. Fix it in the same way. Fixes: 0e0c3fee3a59 ("l2tp: hold reference on tunnels printed in pppol2tp proc file") Fixes: f726214d9b23 ("l2tp: hold reference on tunnels printed in l2tp/tunnels debugfs file") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: hold reference on tunnels printed in l2tp/tunnels debugfs file

2018-04-13T16:17:26+00:00

Use l2tp_tunnel_get_nth() instead of l2tp_tunnel_find_nth(), to be safe against concurrent tunnel deletion. Use the same mechanism as in l2tp_ppp.c for dropping the reference taken by l2tp_tunnel_get_nth(). That is, drop the reference just before looking up the next tunnel. In case of error, drop the last accessed tunnel in l2tp_dfs_seq_stop(). That was the last use of l2tp_tunnel_find_nth(). Fixes: 0ad6614048cf ("l2tp: Add debugfs files for dumping l2tp debug info") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: hold reference on tunnels printed in pppol2tp proc file

2018-04-13T16:17:26+00:00

Use l2tp_tunnel_get_nth() instead of l2tp_tunnel_find_nth(), to be safe against concurrent tunnel deletion. Unlike sessions, we can't drop the reference held on tunnels in pppol2tp_seq_show(). Tunnels are reused across several calls to pppol2tp_seq_start() when iterating over sessions. These iterations need the tunnel for accessing the next session. Therefore the only safe moment for dropping the reference is just before searching for the next tunnel. Normally, the last invocation of pppol2tp_next_tunnel() doesn't find any new tunnel, so it drops the last tunnel without taking any new reference. However, in case of error, pppol2tp_seq_stop() is called directly, so we have to drop the reference there. Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: hold reference on tunnels in netlink dumps

2018-04-13T16:17:26+00:00

l2tp_tunnel_find_nth() is unsafe: no reference is held on the returned tunnel, therefore it can be freed whenever the caller uses it. This patch defines l2tp_tunnel_get_nth() which works similarly, but also takes a reference on the returned tunnel. The caller then has to drop it after it stops using the tunnel. Convert netlink dumps to make them safe against concurrent tunnel deletion. Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: fix race in duplicate tunnel detection

2018-04-11T21:41:27+00:00

We can't use l2tp_tunnel_find() to prevent l2tp_nl_cmd_tunnel_create() from creating a duplicate tunnel. A tunnel can be concurrently registered after l2tp_tunnel_find() returns. Therefore, searching for duplicates must be done at registration time. Finally, remove l2tp_tunnel_find() entirely as it isn't use anywhere anymore. Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

l2tp: fix races in tunnel creation

2018-04-11T21:41:27+00:00

l2tp_tunnel_create() inserts the new tunnel into the namespace's tunnel list and sets the socket's ->sk_user_data field, before returning it to the caller. Therefore, there are two ways the tunnel can be accessed and freed, before the caller even had the opportunity to take a reference. In practice, syzbot could crash the module by closing the socket right after a new tunnel was returned to pppol2tp_create(). This patch moves tunnel registration out of l2tp_tunnel_create(), so that the caller can safely hold a reference before publishing the tunnel. This second step is done with the new l2tp_tunnel_register() function, which is now responsible for associating the tunnel to its socket and for inserting it into the namespace's list. While moving the code to l2tp_tunnel_register(), a few modifications have been done. First, the socket validation tests are done in a helper function, for clarity. Also, modifying the socket is now done after having inserted the tunnel to the namespace's tunnels list. This will allow insertion to fail, without having to revert theses modifications in the error path (a followup patch will check for duplicate tunnels before insertion). Either the socket is a kernel socket which we control, or it is a user-space socket for which we have a reference on the file descriptor. In any case, the socket isn't going to be closed from under us. Reported-by: syzbot+fbeeb5c3b538e8545644@syzkaller.appspotmail.com Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller

net: Drop pernet_operations::async

2018-03-27T17:18:09+00:00

Synchronous pernet_operations are not allowed anymore. All are asynchronous. So, drop the structure member. Signed-off-by: Kirill Tkhai Signed-off-by: David S. Miller