diff options
author | Eric W. Biederman <ebiederm@xmission.com> | 2016-08-08 21:41:24 +0300 |
---|---|---|
committer | Eric W. Biederman <ebiederm@xmission.com> | 2016-08-08 21:41:24 +0300 |
commit | b376c3e1b6770ddcb4f0782be16358095fcea0b6 (patch) | |
tree | 30789f9f1e84abe4d25a52e2fcad209504c181bf /kernel/ucount.c | |
parent | dbec28460a89aa7c02c3301e9e108d98272549d2 (diff) |
userns: Add a limit on the number of user namespaces
Export the export the maximum number of user namespaces as
/proc/sys/userns/max_user_namespaces.
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel/ucount.c')
-rw-r--r-- | kernel/ucount.c | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/kernel/ucount.c b/kernel/ucount.c index cbde1dc87851..6c2205c0befd 100644 --- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -43,7 +43,18 @@ static struct ctl_table_root set_root = { .permissions = set_permissions, }; +static int zero = 0; +static int int_max = INT_MAX; static struct ctl_table userns_table[] = { + { + .procname = "max_user_namespaces", + .data = &init_user_ns.max_user_namespaces, + .maxlen = sizeof(init_user_ns.max_user_namespaces), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + .extra2 = &int_max, + }, { } }; #endif /* CONFIG_SYSCTL */ @@ -55,6 +66,8 @@ bool setup_userns_sysctls(struct user_namespace *ns) setup_sysctl_set(&ns->set, &set_root, set_is_seen); tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL); if (tbl) { + tbl[0].data = &ns->max_user_namespaces; + ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl); } if (!ns->sysctls) { @@ -78,6 +91,46 @@ void retire_userns_sysctls(struct user_namespace *ns) #endif } +static inline bool atomic_inc_below(atomic_t *v, int u) +{ + int c, old; + c = atomic_read(v); + for (;;) { + if (unlikely(c >= u)) + return false; + old = atomic_cmpxchg(v, c, c+1); + if (likely(old == c)) + return true; + c = old; + } +} + +bool inc_user_namespaces(struct user_namespace *ns) +{ + struct user_namespace *pos, *bad; + for (pos = ns; pos; pos = pos->parent) { + int max = READ_ONCE(pos->max_user_namespaces); + if (!atomic_inc_below(&pos->user_namespaces, max)) + goto fail; + } + return true; +fail: + bad = pos; + for (pos = ns; pos != bad; pos = pos->parent) + atomic_dec(&pos->user_namespaces); + + return false; +} + +void dec_user_namespaces(struct user_namespace *ns) +{ + struct user_namespace *pos; + for (pos = ns; pos; pos = pos->parent) { + int dec = atomic_dec_if_positive(&pos->user_namespaces); + WARN_ON_ONCE(dec < 0); + } +} + static __init int user_namespace_sysctl_init(void) { #ifdef CONFIG_SYSCTL |