hi all,
a couple of days ago Paul Starzetz pointed on bugtraq a problem in the linux
kernel regarding a possible DoS:
struct file * get_empty_filp(void)
{
static int old_max = 0;
struct file * f;
file_list_lock();
if (files_stat.nr_free_files > NR_RESERVED_FILES) {
used_one:
f = list_entry(free_list.next, struct file, f_list);
[...]
/*
* Use a reserved one if we're the superuser
*/
[*] if (files_stat.nr_free_files && !current->euid)
goto used_one;
if free fds are == NR_RESERVED_FILES only root can open new files .. but
suid binaries are euid == 0 so an attacker can eat off this reserved fds.
for more information see
http://online.securityfocus.com/archive/1/281100/2002-07-07/2002-07-13/0
and the other posts.
i attached two possible patches:
--- /usr/src/linux/fs/file_table.c Mon Sep 17 20:16:30 2001
+++ /usr/src/linux/fs/file_table.c Mon Jul 8 23:42:01 2002
@@ -51,9 +51,12 @@
return f;
}
/*
- * Use a reserved one if we're the superuser
+ * Use one of the first 16 reserved fds if we have euid == 0
+ * and one of the second 16 reserved fds if we're the superuser
*/
- if (files_stat.nr_free_files && !current->euid)
+ if (files_stat.nr_free_files > (NR_RESERVED_FILES/2) && !current->euid)
+ goto used_one;
+ else if (files_stat.nr_free_files <= (NR_RESERVED_FILES/2) &&
!current->uid)
goto used_one;
/*
* Allocate a new one if we're below the limit.
--- /usr/src/linux/include/linux/fs.h Mon Jul 1 14:48:44 2002
+++ /usr/src/linux/include/linux/fs.h Tue Jul 9 00:07:06 2002
@@ -65,7 +65,7 @@
extern int leases_enable, dir_notify_enable, lease_break_time;
#define NR_FILE 8192 /* this can well be larger on a larger system */
-#define NR_RESERVED_FILES 10 /* reserved for root */
+#define NR_RESERVED_FILES 32 /* first 16 for euid == 0 processes and second
16 only for root */
#define NR_SUPER 256
#define MAY_EXEC 1
excuse me if another patch was submitted but i didnt see it
cheers, elv
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Mon Jul 15 2002 - 22:00:16 EST