From f6110a8fee2ca36f8e2d2abecf3cba9fa7b8ea7d Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Mon, 19 Jun 2017 17:09:55 +0200
Subject: [PATCH 1/1] CVE-2017-1000366: Ignore LD_LIBRARY_PATH for AT_SECURE=1
programs [BZ #21624]
LD_LIBRARY_PATH can only be used to reorder system search paths, which
is not useful functionality.
This makes an exploitable unbounded alloca in _dl_init_paths unreachable
for AT_SECURE=1 programs.
---
elf/rtld.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/elf/rtld.c b/elf/rtld.c
index 2446a87..2269dbe 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -2422,7 +2422,8 @@ process_envvars (enum mode *modep)
case 12:
/* The library search path. */
- if (memcmp (envline, "LIBRARY_PATH", 12) == 0)
+ if (!__libc_enable_secure
+ && memcmp (envline, "LIBRARY_PATH", 12) == 0)
{
library_path = &envline[13];
break;
From 6d0ba622891bed9d8394eef1935add53003b12e8 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Mon, 19 Jun 2017 22:31:04 +0200
Subject: [PATCH] ld.so: Reject overly long LD_PRELOAD path elements
---
elf/rtld.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++------------
1 files changed, 73 insertions(+), 16 deletions(-)
diff --git a/elf/rtld.c b/elf/rtld.c
index 2269dbe..86ae20c 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -99,6 +99,35 @@ uintptr_t __pointer_chk_guard_local
strong_alias (__pointer_chk_guard_local, __pointer_chk_guard)
#endif
+/* Length limits for names and paths, to protect the dynamic linker,
+ particularly when __libc_enable_secure is active. */
+#ifdef NAME_MAX
+# define SECURE_NAME_LIMIT NAME_MAX
+#else
+# define SECURE_NAME_LIMIT 255
+#endif
+#ifdef PATH_MAX
+# define SECURE_PATH_LIMIT PATH_MAX
+#else
+# define SECURE_PATH_LIMIT 1024
+#endif
+
+/* Check that AT_SECURE=0, or that the passed name does not contain
+ directories and is not overly long. Reject empty names
+ unconditionally. */
+static bool
+dso_name_valid_for_suid (const char *p)
+{
+ if (__glibc_unlikely (__libc_enable_secure))
+ {
+ /* Ignore pathnames with directories for AT_SECURE=1
+ programs, and also skip overlong names. */
+ size_t len = strlen (p);
+ if (len >= SECURE_NAME_LIMIT || memchr (p, '/', len) != NULL)
+ return false;
+ }
+ return *p != '\0';
+}
/* List of auditing DSOs. */
static struct audit_list
@@ -718,6 +747,42 @@ static const char *preloadlist attribute_relro;
/* Nonzero if information about versions has to be printed. */
static int version_info attribute_relro;
+/* The LD_PRELOAD environment variable gives list of libraries
+ separated by white space or colons that are loaded before the
+ executable's dependencies and prepended to the global scope list.
+ (If the binary is running setuid all elements containing a '/' are
+ ignored since it is insecure.) Return the number of preloads
+ performed. */
+unsigned int
+handle_ld_preload (const char *preloadlist, struct link_map *main_map)
+{
+ unsigned int npreloads = 0;
+ const char *p = preloadlist;
+ char fname[SECURE_PATH_LIMIT];
+
+ while (*p != '\0')
+ {
+ /* Split preload list at space/colon. */
+ size_t len = strcspn (p, " :");
+ if (len > 0 && len < sizeof (fname))
+ {
+ memcpy (fname, p, len);
+ fname[len] = '\0';
+ }
+ else
+ fname[0] = '\0';
+
+ /* Skip over the substring and the following delimiter. */
+ p += len;
+ if (*p != '\0')
+ ++p;
+
+ if (dso_name_valid_for_suid (fname))
+ npreloads += do_preload (fname, main_map, "LD_PRELOAD");
+ }
+ return npreloads;
+}
+
static void
dl_main (const ElfW(Phdr) *phdr,
ElfW(Word) phnum,
@@ -1464,23 +1529,8 @@ ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
if (__glibc_unlikely (preloadlist != NULL))
{
- /* The LD_PRELOAD environment variable gives list of libraries
- separated by white space or colons that are loaded before the
- executable's dependencies and prepended to the global scope
- list. If the binary is running setuid all elements
- containing a '/' are ignored since it is insecure. */
- char *list = strdupa (preloadlist);
- char *p;
-
HP_TIMING_NOW (start);
-
- /* Prevent optimizing strsep. Speed is not important here. */
- while ((p = (strsep) (&list, " :")) != NULL)
- if (p[0] != '\0'
- && (__builtin_expect (! __libc_enable_secure, 1)
- || strchr (p, '/') == NULL))
- npreloads += do_preload (p, main_map, "LD_PRELOAD");
-
+ npreloads += handle_ld_preload (preloadlist, main_map);
HP_TIMING_NOW (stop);
HP_TIMING_DIFF (diff, start, stop);
HP_TIMING_ACCUM_NT (load_time, diff);
From 81b82fb966ffbd94353f793ad17116c6088dedd9 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Mon, 19 Jun 2017 22:32:12 +0200
Subject: [PATCH] ld.so: Reject overly long LD_AUDIT path elements
Also only process the last LD_AUDIT entry.
---
elf/rtld.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++---------
1 files changed, 106 insertions(+), 15 deletions(-)
diff --git a/elf/rtld.c b/elf/rtld.c
index 86ae20c..65647fb 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -129,13 +129,91 @@ dso_name_valid_for_suid (const char *p)
return *p != '\0';
}
-/* List of auditing DSOs. */
+/* LD_AUDIT variable contents. Must be processed before the
+ audit_list below. */
+const char *audit_list_string;
+
+/* Cyclic list of auditing DSOs. audit_list->next is the first
+ element. */
static struct audit_list
{
const char *name;
struct audit_list *next;
} *audit_list;
+/* Iterator for audit_list_string followed by audit_list. */
+struct audit_list_iter
+{
+ /* Tail of audit_list_string still needing processing, or NULL. */
+ const char *audit_list_tail;
+
+ /* The list element returned in the previous iteration. NULL before
+ the first element. */
+ struct audit_list *previous;
+
+ /* Scratch buffer for returning a name which is part of
+ audit_list_string. */
+ char fname[SECURE_NAME_LIMIT];
+};
+
+/* Initialize an audit list iterator. */
+static void
+audit_list_iter_init (struct audit_list_iter *iter)
+{
+ iter->audit_list_tail = audit_list_string;
+ iter->previous = NULL;
+}
+
+/* Iterate through both audit_list_string and audit_list. */
+static const char *
+audit_list_iter_next (struct audit_list_iter *iter)
+{
+ if (iter->audit_list_tail != NULL)
+ {
+ /* First iterate over audit_list_string. */
+ while (*iter->audit_list_tail != '\0')
+ {
+ /* Split audit list at colon. */
+ size_t len = strcspn (iter->audit_list_tail, ":");
+ if (len > 0 && len < sizeof (iter->fname))
+ {
+ memcpy (iter->fname, iter->audit_list_tail, len);
+ iter->fname[len] = '\0';
+ }
+ else
+ /* Do not return this name to the caller. */
+ iter->fname[0] = '\0';
+
+ /* Skip over the substring and the following delimiter. */
+ iter->audit_list_tail += len;
+ if (*iter->audit_list_tail == ':')
+ ++iter->audit_list_tail;
+
+ /* If the name is valid, return it. */
+ if (dso_name_valid_for_suid (iter->fname))
+ return iter->fname;
+ /* Otherwise, wrap around and try the next name. */
+ }
+ /* Fall through to the procesing of audit_list. */
+ }
+
+ if (iter->previous == NULL)
+ {
+ if (audit_list == NULL)
+ /* No pre-parsed audit list. */
+ return NULL;
+ /* Start of audit list. The first list element is at
+ audit_list->next (cyclic list). */
+ iter->previous = audit_list->next;
+ return iter->previous->name;
+ }
+ if (iter->previous == audit_list)
+ /* Cyclic list wrap-around. */
+ return NULL;
+ iter->previous = iter->previous->next;
+ return iter->previous->name;
+}
+
#ifndef HAVE_INLINED_SYSCALLS
/* Set nonzero during loading and initialization of executable and
libraries, cleared before the executable's entry point runs. This
@@ -1305,11 +1383,13 @@ of this helper program; chances are you did not intend to run this program.\n\
GL(dl_rtld_map).l_tls_modid = _dl_next_tls_modid ();
/* If we have auditing DSOs to load, do it now. */
- if (__glibc_unlikely (audit_list != NULL))
+ bool need_security_init = true;
+ if (__glibc_unlikely (audit_list != NULL)
+ || __glibc_unlikely (audit_list_string != NULL))
{
- /* Iterate over all entries in the list. The order is important. */
struct audit_ifaces *last_audit = NULL;
- struct audit_list *al = audit_list->next;
+ struct audit_list_iter al_iter;
+ audit_list_iter_init (&al_iter);
/* Since we start using the auditing DSOs right away we need to
initialize the data structures now. */
@@ -1320,9 +1400,14 @@ of this helper program; chances are you did not intend to run this program.\n\
use different values (especially the pointer guard) and will
fail later on. */
security_init ();
+ need_security_init = false;
- do
+ while (true)
{
+ const char *name = audit_list_iter_next (&al_iter);
+ if (name == NULL)
+ break;
+
int tls_idx = GL(dl_tls_max_dtv_idx);
/* Now it is time to determine the layout of the static TLS
@@ -1331,7 +1416,7 @@ of this helper program; chances are you did not intend to run this program.\n\
no DF_STATIC_TLS bit is set. The reason is that we know
glibc will use the static model. */
struct dlmopen_args dlmargs;
- dlmargs.fname = al->name;
+ dlmargs.fname = name;
dlmargs.map = NULL;
const char *objname;
@@ -1344,7 +1429,7 @@ of this helper program; chances are you did not intend to run this program.\n\
not_loaded:
_dl_error_printf ("\
ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
- al->name, err_str);
+ name, err_str);
if (malloced)
free ((char *) err_str);
}
@@ -1448,10 +1533,7 @@ ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
goto not_loaded;
}
}
-
- al = al->next;
}
- while (al != audit_list->next);
/* If we have any auditing modules, announce that we already
have two objects loaded. */
@@ -1715,7 +1797,7 @@ ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
if (tcbp == NULL)
tcbp = init_tls ();
- if (__glibc_likely (audit_list == NULL))
+ if (__glibc_likely (need_security_init))
/* Initialize security features. But only if we have not done it
earlier. */
security_init ();
@@ -2346,9 +2428,7 @@ process_dl_audit (char *str)
char *p;
while ((p = (strsep) (&str, ":")) != NULL)
- if (p[0] != '\0'
- && (__builtin_expect (! __libc_enable_secure, 1)
- || strchr (p, '/') == NULL))
+ if (dso_name_valid_for_suid (p))
{
/* This is using the local malloc, not the system malloc. The
memory can never be freed. */
@@ -2412,7 +2492,7 @@ process_envvars (enum mode *modep)
break;
}
if (memcmp (envline, "AUDIT", 5) == 0)
- process_dl_audit (&envline[6]);
+ audit_list_string = &envline[6];
break;
case 7: