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355 lines
9.4 KiB
355 lines
9.4 KiB
From bfee1a3131580a7b9d8a7366764b8e78d99a9f1b Mon Sep 17 00:00:00 2001
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From: Petr Lautrbach <plautrba@redhat.com>
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Date: Mon, 17 Feb 2020 21:47:35 +0100
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Subject: [PATCH] libselinux: Eliminate use of security_compute_user()
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get_ordered_context_list() code used to ask the kernel to compute the complete
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set of reachable contexts using /sys/fs/selinux/user aka
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security_compute_user(). This set can be so huge so that it doesn't fit into a
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kernel page and security_compute_user() fails. Even if it doesn't fail,
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get_ordered_context_list() throws away the vast majority of the returned
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contexts because they don't match anything in
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/etc/selinux/targeted/contexts/default_contexts or
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/etc/selinux/targeted/contexts/users/
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get_ordered_context_list() is rewritten to compute set of contexts based on
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/etc/selinux/targeted/contexts/users/ and
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/etc/selinux/targeted/contexts/default_contexts files and to return only valid
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contexts, using security_check_context(), from this set.
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Fixes: https://github.com/SELinuxProject/selinux/issues/28
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Signed-off-by: Petr Lautrbach <plautrba@redhat.com>
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---
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libselinux/src/get_context_list.c | 212 +++++++++++++-----------------
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1 file changed, 93 insertions(+), 119 deletions(-)
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diff --git a/libselinux/src/get_context_list.c b/libselinux/src/get_context_list.c
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index 689e4658..26d7b3b9 100644
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--- a/libselinux/src/get_context_list.c
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+++ b/libselinux/src/get_context_list.c
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@@ -2,6 +2,7 @@
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#include <errno.h>
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#include <stdio.h>
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#include <stdio_ext.h>
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+#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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@@ -114,64 +115,41 @@ int get_default_context(const char *user,
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return 0;
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}
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-static int find_partialcon(char ** list,
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- unsigned int nreach, char *part)
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+static int is_in_reachable(char **reachable, const char *usercon_str)
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{
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- const char *conrole, *contype;
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- char *partrole, *parttype, *ptr;
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- context_t con;
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- unsigned int i;
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+ if (!reachable)
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+ return 0;
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- partrole = part;
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- ptr = part;
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- while (*ptr && !isspace(*ptr) && *ptr != ':')
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- ptr++;
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- if (*ptr != ':')
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- return -1;
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- *ptr++ = 0;
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- parttype = ptr;
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- while (*ptr && !isspace(*ptr) && *ptr != ':')
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- ptr++;
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- *ptr = 0;
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-
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- for (i = 0; i < nreach; i++) {
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- con = context_new(list[i]);
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- if (!con)
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- return -1;
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- conrole = context_role_get(con);
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- contype = context_type_get(con);
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- if (!conrole || !contype) {
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- context_free(con);
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- return -1;
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- }
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- if (!strcmp(conrole, partrole) && !strcmp(contype, parttype)) {
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- context_free(con);
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- return i;
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+ for (; *reachable != NULL; reachable++) {
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+ if (strcmp(*reachable, usercon_str) == 0) {
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+ return 1;
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}
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- context_free(con);
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}
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-
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- return -1;
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+ return 0;
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}
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-static int get_context_order(FILE * fp,
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+static int get_context_user(FILE * fp,
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char * fromcon,
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- char ** reachable,
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- unsigned int nreach,
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- unsigned int *ordering, unsigned int *nordered)
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+ const char * user,
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+ char ***reachable,
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+ unsigned int *nreachable)
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{
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char *start, *end = NULL;
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char *line = NULL;
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- size_t line_len = 0;
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+ size_t line_len = 0, usercon_len;
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+ size_t user_len = strlen(user);
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ssize_t len;
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int found = 0;
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- const char *fromrole, *fromtype;
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+ const char *fromrole, *fromtype, *fromlevel;
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char *linerole, *linetype;
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- unsigned int i;
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+ char **new_reachable = NULL;
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+ char *usercon_str;
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context_t con;
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+ context_t usercon;
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+
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int rc;
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- errno = -EINVAL;
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+ errno = EINVAL;
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/* Extract the role and type of the fromcon for matching.
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User identity and MLS range can be variable. */
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@@ -180,6 +158,7 @@ static int get_context_order(FILE * fp,
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return -1;
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fromrole = context_role_get(con);
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fromtype = context_type_get(con);
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+ fromlevel = context_range_get(con);
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if (!fromrole || !fromtype) {
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context_free(con);
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return -1;
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@@ -243,23 +222,75 @@ static int get_context_order(FILE * fp,
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if (*end)
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*end++ = 0;
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- /* Check for a match in the reachable list. */
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- rc = find_partialcon(reachable, nreach, start);
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- if (rc < 0) {
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- /* No match, skip it. */
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+ /* Check whether a new context is valid */
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+ if (SIZE_MAX - user_len < strlen(start) + 2) {
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+ fprintf(stderr, "%s: one of partial contexts is too big\n", __FUNCTION__);
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+ errno = EINVAL;
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+ rc = -1;
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+ goto out;
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+ }
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+ usercon_len = user_len + strlen(start) + 2;
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+ usercon_str = malloc(usercon_len);
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+ if (!usercon_str) {
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+ rc = -1;
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+ goto out;
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+ }
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+
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+ /* set range from fromcon in the new usercon */
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+ snprintf(usercon_str, usercon_len, "%s:%s", user, start);
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+ usercon = context_new(usercon_str);
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+ if (!usercon) {
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+ if (errno != EINVAL) {
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+ free(usercon_str);
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+ rc = -1;
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+ goto out;
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+ }
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+ fprintf(stderr,
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+ "%s: can't create a context from %s, skipping\n",
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+ __FUNCTION__, usercon_str);
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+ free(usercon_str);
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start = end;
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continue;
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}
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+ free(usercon_str);
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+ if (context_range_set(usercon, fromlevel) != 0) {
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+ context_free(usercon);
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+ rc = -1;
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+ goto out;
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+ }
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+ usercon_str = context_str(usercon);
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+ if (!usercon_str) {
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+ context_free(usercon);
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+ rc = -1;
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+ goto out;
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+ }
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- /* If a match is found and the entry is not already ordered
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- (e.g. due to prior match in prior config file), then set
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- the ordering for it. */
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- i = rc;
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- if (ordering[i] == nreach)
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- ordering[i] = (*nordered)++;
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+ /* check whether usercon is already in reachable */
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+ if (is_in_reachable(*reachable, usercon_str)) {
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+ context_free(usercon);
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+ start = end;
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+ continue;
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+ }
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+ if (security_check_context(usercon_str) == 0) {
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+ new_reachable = realloc(*reachable, (*nreachable + 2) * sizeof(char *));
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+ if (!new_reachable) {
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+ context_free(usercon);
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+ rc = -1;
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+ goto out;
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+ }
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+ *reachable = new_reachable;
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+ new_reachable[*nreachable] = strdup(usercon_str);
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+ if (new_reachable[*nreachable] == NULL) {
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+ context_free(usercon);
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+ rc = -1;
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+ goto out;
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+ }
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+ new_reachable[*nreachable + 1] = 0;
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+ *nreachable += 1;
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+ }
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+ context_free(usercon);
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start = end;
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}
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-
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rc = 0;
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out:
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@@ -313,21 +344,6 @@ static int get_failsafe_context(const char *user, char ** newcon)
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return 0;
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}
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-struct context_order {
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- char * con;
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- unsigned int order;
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-};
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-
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-static int order_compare(const void *A, const void *B)
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-{
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- const struct context_order *c1 = A, *c2 = B;
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- if (c1->order < c2->order)
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- return -1;
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- else if (c1->order > c2->order)
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- return 1;
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- return strcmp(c1->con, c2->con);
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-}
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-
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int get_ordered_context_list_with_level(const char *user,
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const char *level,
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char * fromcon,
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@@ -395,11 +411,8 @@ int get_ordered_context_list(const char *user,
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char *** list)
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{
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char **reachable = NULL;
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- unsigned int *ordering = NULL;
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- struct context_order *co = NULL;
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- char **ptr;
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int rc = 0;
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- unsigned int nreach = 0, nordered = 0, freefrom = 0, i;
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+ unsigned nreachable = 0, freefrom = 0;
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FILE *fp;
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char *fname = NULL;
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size_t fname_len;
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@@ -413,23 +426,6 @@ int get_ordered_context_list(const char *user,
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freefrom = 1;
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}
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- /* Determine the set of reachable contexts for the user. */
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- rc = security_compute_user(fromcon, user, &reachable);
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- if (rc < 0)
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- goto failsafe;
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- nreach = 0;
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- for (ptr = reachable; *ptr; ptr++)
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- nreach++;
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- if (!nreach)
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- goto failsafe;
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-
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- /* Initialize ordering array. */
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- ordering = malloc(nreach * sizeof(unsigned int));
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- if (!ordering)
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- goto failsafe;
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- for (i = 0; i < nreach; i++)
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- ordering[i] = nreach;
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-
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/* Determine the ordering to apply from the optional per-user config
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and from the global config. */
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fname_len = strlen(user_contexts_path) + strlen(user) + 2;
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@@ -440,8 +436,8 @@ int get_ordered_context_list(const char *user,
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fp = fopen(fname, "re");
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if (fp) {
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__fsetlocking(fp, FSETLOCKING_BYCALLER);
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- rc = get_context_order(fp, fromcon, reachable, nreach, ordering,
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- &nordered);
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+ rc = get_context_user(fp, fromcon, user, &reachable, &nreachable);
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+
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fclose(fp);
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if (rc < 0 && errno != ENOENT) {
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fprintf(stderr,
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@@ -454,8 +450,7 @@ int get_ordered_context_list(const char *user,
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fp = fopen(selinux_default_context_path(), "re");
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if (fp) {
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__fsetlocking(fp, FSETLOCKING_BYCALLER);
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- rc = get_context_order(fp, fromcon, reachable, nreach, ordering,
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- &nordered);
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+ rc = get_context_user(fp, fromcon, user, &reachable, &nreachable);
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fclose(fp);
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if (rc < 0 && errno != ENOENT) {
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fprintf(stderr,
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@@ -463,40 +458,19 @@ int get_ordered_context_list(const char *user,
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__FUNCTION__, selinux_default_context_path());
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/* Fall through */
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}
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- rc = 0;
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}
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- if (!nordered)
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+ if (!nreachable)
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goto failsafe;
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- /* Apply the ordering. */
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- co = malloc(nreach * sizeof(struct context_order));
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- if (!co)
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- goto failsafe;
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- for (i = 0; i < nreach; i++) {
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- co[i].con = reachable[i];
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- co[i].order = ordering[i];
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- }
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- qsort(co, nreach, sizeof(struct context_order), order_compare);
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- for (i = 0; i < nreach; i++)
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- reachable[i] = co[i].con;
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- free(co);
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-
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- /* Only report the ordered entries to the caller. */
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- if (nordered <= nreach) {
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- for (i = nordered; i < nreach; i++)
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- free(reachable[i]);
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- reachable[nordered] = NULL;
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- rc = nordered;
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- }
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-
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out:
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- if (rc > 0)
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+ if (nreachable > 0) {
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*list = reachable;
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+ rc = nreachable;
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+ }
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else
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freeconary(reachable);
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- free(ordering);
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if (freefrom)
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freecon(fromcon);
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@@ -519,7 +493,7 @@ int get_ordered_context_list(const char *user,
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reachable = NULL;
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goto out;
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}
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- rc = 1; /* one context in the list */
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+ nreachable = 1; /* one context in the list */
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goto out;
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}
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--
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2.25.4
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