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From 5d52fa8c3c903df4be0e4e954fbca9b3b15285c6 Mon Sep 17 00:00:00 2001
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From: Klaus Wenninger <klaus.wenninger@aon.at>
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Date: Fri, 14 Sep 2018 17:51:50 +0200
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Subject: [PATCH] Fix: sbd-common: don't follow symlinks outside /dev for
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watchdog
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This makes it easier to define a SELinux-policy that keeps
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avc-log clean on /dev traversal triggered by query-watchdog.
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---
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src/sbd-common.c | 42 ++++++++++++++++++++++++++++++++++++++----
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1 file changed, 38 insertions(+), 4 deletions(-)
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diff --git a/src/sbd-common.c b/src/sbd-common.c
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index 0ce6478..fcb7a31 100644
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--- a/src/sbd-common.c
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+++ b/src/sbd-common.c
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@@ -251,7 +251,8 @@ watchdog_close(bool disarm)
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#define MAX_WATCHDOGS 64
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#define SYS_CLASS_WATCHDOG "/sys/class/watchdog"
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#define SYS_CHAR_DEV_DIR "/sys/dev/char"
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-#define WATCHDOG_NODEDIR "/dev"
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+#define WATCHDOG_NODEDIR "/dev/"
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+#define WATCHDOG_NODEDIR_LEN 5
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struct watchdog_list_item {
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dev_t dev;
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@@ -273,7 +274,7 @@ watchdog_populate_list(void)
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struct dirent *entry;
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char entry_name[280];
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DIR *dp;
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- char buf[256] = "";
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+ char buf[280] = "";
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if (watchdog_list != NULL) {
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return;
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@@ -313,7 +314,38 @@ watchdog_populate_list(void)
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struct stat statbuf;
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snprintf(entry_name, sizeof(entry_name),
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- WATCHDOG_NODEDIR "/%s", entry->d_name);
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+ WATCHDOG_NODEDIR "%s", entry->d_name);
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+ if (entry->d_type == DT_LNK) {
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+ int len;
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+
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+ /* !realpath(entry_name, buf) unfortunately does a stat on
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+ * target so we can't really use it to check if links stay
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+ * within /dev without triggering e.g. AVC-logs (with
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+ * SELinux policy that just allows stat within /dev).
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+ * Without canonicalization that doesn't actually touch the
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+ * filesystem easily available introduce some limitations
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+ * for simplicity:
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+ * - just simple path without '..'
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+ * - just one level of symlinks (avoid e.g. loop-checking)
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+ */
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+ len = readlink(entry_name, buf, sizeof(buf) - 1);
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+ if ((len < 1) ||
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+ (len > sizeof(buf) - WATCHDOG_NODEDIR_LEN - 1)) {
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+ continue;
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+ }
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+ buf[len] = '\0';
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+ if (buf[0] != '/') {
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+ memmove(&buf[WATCHDOG_NODEDIR_LEN], buf, len+1);
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+ memcpy(buf, WATCHDOG_NODEDIR, WATCHDOG_NODEDIR_LEN);
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+ len += WATCHDOG_NODEDIR_LEN;
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+ }
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+ if (strstr(buf, "/../") ||
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+ strncmp(WATCHDOG_NODEDIR, buf, WATCHDOG_NODEDIR_LEN) ||
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+ lstat(buf, &statbuf) ||
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+ !S_ISCHR(statbuf.st_mode)) {
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+ continue;
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+ }
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+ }
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if(!stat(entry_name, &statbuf) && S_ISCHR(statbuf.st_mode)) {
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int i;
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@@ -322,6 +354,7 @@ watchdog_populate_list(void)
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int wdfd = watchdog_init_fd(entry_name, -1);
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struct watchdog_list_item *wdg =
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calloc(1, sizeof(struct watchdog_list_item));
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+ int len;
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wdg->dev = watchdogs[i];
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wdg->dev_node = strdup(entry_name);
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@@ -343,7 +376,8 @@ watchdog_populate_list(void)
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snprintf(entry_name, sizeof(entry_name),
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SYS_CHAR_DEV_DIR "/%d:%d/device/driver",
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major(watchdogs[i]), minor(watchdogs[i]));
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- if (readlink(entry_name, buf, sizeof(buf)) > 0) {
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+ if ((len = readlink(entry_name, buf, sizeof(buf) - 1)) > 0) {
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+ buf[len] = '\0';
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wdg->dev_driver = strdup(basename(buf));
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} else if ((wdg->dev_ident) &&
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(strcmp(wdg->dev_ident,
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--
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1.8.3.1
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