From d183654ec1a2cd1149bdb92601ccb7246bddb14e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 25 Jul 2018 19:56:54 +0200 Subject: [PATCH] CVE 2018-6556: verify netns fd in lxc-user-nic Signed-off-by: Christian Brauner --- src/lxc/lxc_user_nic.c | 35 ++++++++++++++++++++++++++++++++--- src/lxc/utils.c | 12 ++++++++++++ src/lxc/utils.h | 5 +++++ 3 files changed, 49 insertions(+), 3 deletions(-) ADDENDUM from vdupras@gentoo.org: Original patch from Christian didn't include LXC_PROC_PID_FD_LEN define, but referenced it. This resulted in code that doesn't compile. I fetched the definition from the stable-3.0 branch and included it to this patch. Also, this diff is regenerated from lxc-2.1.1 tag instead of stable-2.0 branch. Patch-Source: https://github.com/gentoo/gentoo/blob/4c6e73df9d616d5c472c276dd5bef70efea02907/app-emulation/lxc/files/lxc-2.1.1-cve-2018-6556.patch diff --git a/src/lxc/lxc_user_nic.c b/src/lxc/lxc_user_nic.c index 6f550f0d..09a342ac 100644 --- a/src/lxc/lxc_user_nic.c +++ b/src/lxc/lxc_user_nic.c @@ -1124,12 +1124,41 @@ int main(int argc, char *argv[]) exit(EXIT_FAILURE); } } else if (request == LXC_USERNIC_DELETE) { - netns_fd = open(args.pid, O_RDONLY); + char opath[LXC_PROC_PID_FD_LEN]; + + /* Open the path with O_PATH which will not trigger an actual + * open(). Don't report an errno to the caller to not leak + * information whether the path exists or not. + * When stracing setuid is stripped so this is not a concern + * either. + */ + netns_fd = open(args.pid, O_PATH | O_CLOEXEC); if (netns_fd < 0) { - usernic_error("Could not open \"%s\": %s\n", args.pid, - strerror(errno)); + usernic_error("Failed to open \"%s\"\n", args.pid); exit(EXIT_FAILURE); } + + if (!fhas_fs_type(netns_fd, NSFS_MAGIC)) { + usernic_error("Path \"%s\" does not refer to a network namespace path\n", args.pid); + close(netns_fd); + exit(EXIT_FAILURE); + } + + ret = snprintf(opath, sizeof(opath), "/proc/self/fd/%d", netns_fd); + if (ret < 0 || (size_t)ret >= sizeof(opath)) { + close(netns_fd); + exit(EXIT_FAILURE); + } + + /* Now get an fd that we can use in setns() calls. */ + ret = open(opath, O_RDONLY | O_CLOEXEC); + if (ret < 0) { + usernic_error("Failed to open \"%s\": %s\n", args.pid, strerror(errno)); + close(netns_fd); + exit(EXIT_FAILURE); + } + close(netns_fd); + netns_fd = ret; } if (!create_db_dir(LXC_USERNIC_DB)) { diff --git a/src/lxc/utils.c b/src/lxc/utils.c index e6a44a51..c2a08a9d 100644 --- a/src/lxc/utils.c +++ b/src/lxc/utils.c @@ -2380,6 +2380,18 @@ bool has_fs_type(const char *path, fs_type_magic magic_val) return has_type; } +bool fhas_fs_type(int fd, fs_type_magic magic_val) +{ + int ret; + struct statfs sb; + + ret = fstatfs(fd, &sb); + if (ret < 0) + return false; + + return is_fs_type(&sb, magic_val); +} + bool lxc_nic_exists(char *nic) { #define __LXC_SYS_CLASS_NET_LEN 15 + IFNAMSIZ + 1 diff --git a/src/lxc/utils.h b/src/lxc/utils.h index e83ed49e..06ec74d7 100644 --- a/src/lxc/utils.h +++ b/src/lxc/utils.h @@ -46,11 +46,16 @@ #define __S_ISTYPE(mode, mask) (((mode)&S_IFMT) == (mask)) #endif +#ifndef NSFS_MAGIC +#define NSFS_MAGIC 0x6e736673 +#endif + /* Useful macros */ /* Maximum number for 64 bit integer is a string with 21 digits: 2^64 - 1 = 21 */ #define LXC_NUMSTRLEN64 21 #define LXC_LINELEN 4096 #define LXC_IDMAPLEN 4096 +#define LXC_PROC_PID_FD_LEN (6 + LXC_NUMSTRLEN64 + 4 + LXC_NUMSTRLEN64 + 1) /* returns 1 on success, 0 if there were any failures */ extern int lxc_rmdir_onedev(char *path, const char *exclude); @@ -402,6 +407,7 @@ extern void *must_realloc(void *orig, size_t sz); /* __typeof__ should be safe to use with all compilers. */ typedef __typeof__(((struct statfs *)NULL)->f_type) fs_type_magic; extern bool has_fs_type(const char *path, fs_type_magic magic_val); +extern bool fhas_fs_type(int fd, fs_type_magic magic_val); extern bool is_fs_type(const struct statfs *fs, fs_type_magic magic_val); extern bool lxc_nic_exists(char *nic);