From: Daniel Borkmann daniel@iogearbox.net

commit f7bd9e36ee4a4ce38e1cddd7effe6c0d9943285b upstream

Add a bpf_check_basics_ok() and reject filters that are of invalid size much earlier, so we don't do any useless work such as invoking bpf_prog_alloc(). Currently, rejection happens in bpf_check_classic() only, but it's really unnecessarily late and they should be rejected at earliest point. While at it, also clean up one bpf_prog_size() to make it consistent with the remaining invocations.

Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Alexei Starovoitov ast@kernel.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Zubin Mithra zsm@chromium.org --- Notes: * Syzkaller reported a kernel BUG related to a kernel paging request in bpf_prog_create with the following stacktrace when fuzzing a 4.4 kernel. Call Trace: [<ffffffff822ac1c8>] bpf_prog_create+0xc8/0x210 net/core/filter.c:1067 [<ffffffff82454699>] bpf_mt_check+0xb9/0x120 net/netfilter/xt_bpf.c:31 [<ffffffff82437db8>] xt_check_match+0x238/0x730 net/netfilter/x_tables.c:409 [<ffffffff82940254>] ebt_check_match net/bridge/netfilter/ebtables.c:380 [inline] [<ffffffff82940254>] ebt_check_entry+0x844/0x1740 net/bridge/netfilter/ebtables.c:709 [<ffffffff82946842>] translate_table+0xcb2/0x1e80 net/bridge/netfilter/ebtables.c:946 [<ffffffff8294a918>] do_replace_finish+0x6e8/0x1fd0 net/bridge/netfilter/ebtables.c:1002 [<ffffffff8294c419>] do_replace+0x219/0x370 net/bridge/netfilter/ebtables.c:1145 [<ffffffff8294c649>] do_ebt_set_ctl+0xd9/0x110 net/bridge/netfilter/ebtables.c:1492 [<ffffffff8239a87c>] nf_sockopt net/netfilter/nf_sockopt.c:105 [inline] [<ffffffff8239a87c>] nf_setsockopt+0x6c/0xc0 net/netfilter/nf_sockopt.c:114 [<ffffffff825ddeb6>] ip_setsockopt+0xa6/0xc0 net/ipv4/ip_sockglue.c:1226 [<ffffffff825fd3c7>] tcp_setsockopt+0x87/0xd0 net/ipv4/tcp.c:2701 [<ffffffff8220343a>] sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:2690 [<ffffffff822006ed>] SYSC_setsockopt net/socket.c:1767 [inline] [<ffffffff822006ed>] SyS_setsockopt+0x15d/0x240 net/socket.c:1746 [<ffffffff82a16f9b>] entry_SYSCALL_64_fastpath+0x18/0x94

* This patch resolves the following conflicts when applying to v4.4.y: - __get_filter does not exist in v4.4. Instead the checks are moved into __sk_attach_filter.

* This patch is present in v4.9.y.

* Tests run: Chrome OS tryjobs, Syzkaller reproducer

net/core/filter.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c index 1a9ded6af138..3c5f51198c41 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -742,6 +742,17 @@ static bool chk_code_allowed(u16 code_to_probe) return codes[code_to_probe]; }

+static bool bpf_check_basics_ok(const struct sock_filter *filter, + unsigned int flen) +{ + if (filter == NULL) + return false; + if (flen == 0 || flen > BPF_MAXINSNS) + return false; + + return true; +} + /** * bpf_check_classic - verify socket filter code * @filter: filter to verify @@ -762,9 +773,6 @@ static int bpf_check_classic(const struct sock_filter *filter, bool anc_found; int pc;

- if (flen == 0 || flen > BPF_MAXINSNS) - return -EINVAL; - /* Check the filter code now */ for (pc = 0; pc < flen; pc++) { const struct sock_filter *ftest = &filter[pc]; @@ -1057,7 +1065,7 @@ int bpf_prog_create(struct bpf_prog **pfp, struct sock_fprog_kern *fprog) struct bpf_prog *fp;

/* Make sure new filter is there and in the right amounts. */ - if (fprog->filter == NULL) + if (!bpf_check_basics_ok(fprog->filter, fprog->len)) return -EINVAL;

fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0); @@ -1104,7 +1112,7 @@ int bpf_prog_create_from_user(struct bpf_prog **pfp, struct sock_fprog *fprog, int err;

/* Make sure new filter is there and in the right amounts. */ - if (fprog->filter == NULL) + if (!bpf_check_basics_ok(fprog->filter, fprog->len)) return -EINVAL;

fp = bpf_prog_alloc(bpf_prog_size(fprog->len), 0); @@ -1184,7 +1192,6 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk, bool locked) { unsigned int fsize = bpf_classic_proglen(fprog); - unsigned int bpf_fsize = bpf_prog_size(fprog->len); struct bpf_prog *prog; int err;

@@ -1192,10 +1199,10 @@ int __sk_attach_filter(struct sock_fprog *fprog, struct sock *sk, return -EPERM;

/* Make sure new filter is there and in the right amounts. */ - if (fprog->filter == NULL) + if (!bpf_check_basics_ok(fprog->filter, fprog->len)) return -EINVAL;

- prog = bpf_prog_alloc(bpf_fsize, 0); + prog = bpf_prog_alloc(bpf_prog_size(fprog->len), 0); if (!prog) return -ENOMEM;