env: considerably beef up environment cleaning logic

Now, actually check if the environment variable names and values used
are valid, before accepting them. With this in place are at some places
more rigid than POSIX, and less rigid at others. For example, this code
allows lower-case environment variables (which POSIX suggests not to
use), but it will not allow non-UTF8 variable values.

All in all this should be a good middle ground of what to allow and what
not to allow as environment variables.

(This also splits out all environment related calls into env-util.[ch])

1 files changed, 394 insertions, 0 deletions

diff --git a/src/shared/env-util.c b/src/shared/env-util.c
new file mode 100644
index 0000000000..7a213a77c0
--- /dev/null
+++ b/src/shared/env-util.c
@@ -0,0 +1,394 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <limits.h>
+#include <sys/param.h>
+#include <unistd.h>
+
+#include "strv.h"
+#include "utf8.h"
+#include "util.h"
+#include "env-util.h"
+
+#define VALID_CHARS_ENV_NAME                    \
+        "0123456789"                            \
+        "abcdefghijklmnopqrstuvwxyz"            \
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"            \
+        "_"
+
+#ifndef ARG_MAX
+#define ARG_MAX ((size_t) sysconf(_SC_ARG_MAX))
+#endif
+
+static bool env_name_is_valid_n(const char *e, size_t n) {
+        const char *p;
+
+        if (!e)
+                return false;
+
+        if (n <= 0)
+                return false;
+
+        if (e[0] >= '0' && e[0] <= '9')
+                return false;
+
+        /* POSIX says the overall size of the environment block cannot
+         * be > ARG_MAX, an individual assignment hence cannot be
+         * either. Discounting the equal sign and trailing NUL this
+         * hence leaves ARG_MAX-2 as longest possible variable
+         * name. */
+        if (n > ARG_MAX - 2)
+                return false;
+
+        for (p = e; p < e + n; p++)
+                if (!strchr(VALID_CHARS_ENV_NAME, *p))
+                        return false;
+
+        return true;
+}
+
+bool env_name_is_valid(const char *e) {
+        if (!e)
+                return false;
+
+        return env_name_is_valid_n(e, strlen(e));
+}
+
+bool env_value_is_valid(const char *e) {
+        if (!e)
+                return false;
+
+        if (!utf8_is_valid(e))
+                return false;
+
+        if (string_has_cc(e))
+                return false;
+
+        /* POSIX says the overall size of the environment block cannot
+         * be > ARG_MAX, an individual assignment hence cannot be
+         * either. Discounting the shortest possible variable name of
+         * length 1, the equal sign and trailing NUL this hence leaves
+         * ARG_MAX-3 as longest possible variable value. */
+        if (strlen(e) > ARG_MAX - 3)
+                return false;
+
+        return true;
+}
+
+bool env_assignment_is_valid(const char *e) {
+        const char *eq;
+
+        eq = strchr(e, '=');
+        if (!eq)
+                return false;
+
+        if (!env_name_is_valid_n(e, eq - e))
+                return false;
+
+        if (!env_value_is_valid(eq + 1))
+                return false;
+
+        /* POSIX says the overall size of the environment block cannot
+         * be > ARG_MAX, hence the individual variable assignments
+         * cannot be either, but let's room for one trailing NUL
+         * byte. */
+        if (strlen(e) > ARG_MAX - 1)
+                return false;
+
+        return true;
+}
+
+bool strv_env_is_valid(char **e) {
+        char **p, **q;
+
+        STRV_FOREACH(p, e) {
+                size_t k;
+
+                if (!env_assignment_is_valid(*p))
+                        return false;
+
+                /* Check if there are duplicate assginments */
+                k = strcspn(*p, "=");
+                STRV_FOREACH(q, p + 1)
+                        if (strncmp(*p, *q, k) == 0 && (*q)[k] == '=')
+                                return false;
+        }
+
+        return true;
+}
+
+static int env_append(char **r, char ***k, char **a) {
+        assert(r);
+        assert(k);
+
+        if (!a)
+                return 0;
+
+        /* Add the entries of a to *k unless they already exist in *r
+         * in which case they are overridden instead. This assumes
+         * there is enough space in the r array. */
+
+        for (; *a; a++) {
+                char **j;
+                size_t n;
+
+                n = strcspn(*a, "=");
+
+                if ((*a)[n] == '=')
+                        n++;
+
+                for (j = r; j < *k; j++)
+                        if (strncmp(*j, *a, n) == 0)
+                                break;
+
+                if (j >= *k)
+                        (*k)++;
+                else
+                        free(*j);
+
+                *j = strdup(*a);
+                if (!*j)
+                        return -ENOMEM;
+        }
+
+        return 0;
+}
+
+char **strv_env_merge(unsigned n_lists, ...) {
+        size_t n = 0;
+        char **l, **k, **r;
+        va_list ap;
+        unsigned i;
+
+        /* Merges an arbitrary number of environment sets */
+
+        va_start(ap, n_lists);
+        for (i = 0; i < n_lists; i++) {
+                l = va_arg(ap, char**);
+                n += strv_length(l);
+        }
+        va_end(ap);
+
+        r = new(char*, n+1);
+        if (!r)
+                return NULL;
+
+        k = r;
+
+        va_start(ap, n_lists);
+        for (i = 0; i < n_lists; i++) {
+                l = va_arg(ap, char**);
+                if (env_append(r, &k, l) < 0)
+                        goto fail;
+        }
+        va_end(ap);
+
+        *k = NULL;
+
+        return r;
+
+fail:
+        va_end(ap);
+        strv_free(r);
+
+        return NULL;
+}
+
+static bool env_match(const char *t, const char *pattern) {
+        assert(t);
+        assert(pattern);
+
+        /* pattern a matches string a
+         *         a matches a=
+         *         a matches a=b
+         *         a= matches a=
+         *         a=b matches a=b
+         *         a= does not match a
+         *         a=b does not match a=
+         *         a=b does not match a
+         *         a=b does not match a=c */
+
+        if (streq(t, pattern))
+                return true;
+
+        if (!strchr(pattern, '=')) {
+                size_t l = strlen(pattern);
+
+                return strncmp(t, pattern, l) == 0 && t[l] == '=';
+        }
+
+        return false;
+}
+
+char **strv_env_delete(char **x, unsigned n_lists, ...) {
+        size_t n, i = 0;
+        char **k, **r;
+        va_list ap;
+
+        /* Deletes every entry from x that is mentioned in the other
+         * string lists */
+
+        n = strv_length(x);
+
+        r = new(char*, n+1);
+        if (!r)
+                return NULL;
+
+        STRV_FOREACH(k, x) {
+                unsigned v;
+
+                va_start(ap, n_lists);
+                for (v = 0; v < n_lists; v++) {
+                        char **l, **j;
+
+                        l = va_arg(ap, char**);
+                        STRV_FOREACH(j, l)
+                                if (env_match(*k, *j))
+                                        goto skip;
+                }
+                va_end(ap);
+
+                r[i] = strdup(*k);
+                if (!r[i]) {
+                        strv_free(r);
+                        return NULL;
+                }
+
+                i++;
+                continue;
+
+        skip:
+                va_end(ap);
+        }
+
+        r[i] = NULL;
+
+        assert(i <= n);
+
+        return r;
+}
+
+char **strv_env_unset(char **l, const char *p) {
+
+        char **f, **t;
+
+        if (!l)
+                return NULL;
+
+        assert(p);
+
+        /* Drops every occurrence of the env var setting p in the
+         * string list. edits in-place. */
+
+        for (f = t = l; *f; f++) {
+
+                if (env_match(*f, p)) {
+                        free(*f);
+                        continue;
+                }
+
+                *(t++) = *f;
+        }
+
+        *t = NULL;
+        return l;
+}
+
+char **strv_env_set(char **x, const char *p) {
+
+        char **k, **r;
+        char* m[2] = { (char*) p, NULL };
+
+        /* Overrides the env var setting of p, returns a new copy */
+
+        r = new(char*, strv_length(x)+2);
+        if (!r)
+                return NULL;
+
+        k = r;
+        if (env_append(r, &k, x) < 0)
+                goto fail;
+
+        if (env_append(r, &k, m) < 0)
+                goto fail;
+
+        *k = NULL;
+
+        return r;
+
+fail:
+        strv_free(r);
+        return NULL;
+}
+
+char *strv_env_get_n(char **l, const char *name, size_t k) {
+        char **i;
+
+        assert(name);
+
+        if (k <= 0)
+                return NULL;
+
+        STRV_FOREACH(i, l)
+                if (strncmp(*i, name, k) == 0 &&
+                    (*i)[k] == '=')
+                        return *i + k + 1;
+
+        return NULL;
+}
+
+char *strv_env_get(char **l, const char *name) {
+        assert(name);
+
+        return strv_env_get_n(l, name, strlen(name));
+}
+
+char **strv_env_clean(char **e) {
+        char **p, **q;
+        int k = 0;
+
+        STRV_FOREACH(p, e) {
+                size_t n;
+                bool duplicate = false;
+
+                if (!env_assignment_is_valid(*p)) {
+                        free(*p);
+                        continue;
+                }
+
+                n = strcspn(*p, "=");
+                STRV_FOREACH(q, p + 1)
+                        if (strncmp(*p, *q, n) == 0 && (*q)[n] == '=') {
+                                duplicate = true;
+                                break;
+                        }
+
+                if (duplicate) {
+                        free(*p);
+                        continue;
+                }
+
+                e[k++] = *p;
+        }
+
+        e[k] = NULL;
+        return e;
+}