Messages in this thread Patch in this message | | | From | elv@openbeer ... | Subject | [PATCH] Fwd from bugtraq: Linux kernels DoSable by file-max limit | Date | Wed, 10 Jul 2002 01:10:31 GMT |
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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/
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