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[PATCH] ld.so: Reject overly long LD_PRELOAD path elements
- From: fweimer at redhat dot com (Florian Weimer)
- To: libc-alpha at sourceware dot org
- Date: Mon, 19 Jun 2017 18:13:25 +0200
- Subject: [PATCH] ld.so: Reject overly long LD_PRELOAD path elements
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2017-06-19 Florian Weimer <fweimer@redhat.com>
* elf/rtld.c (dso_name_valid_for_suid): New function.
(handle_ld_preload): Likewise.
(dl_main): Call it. Remove alloca.
diff --git a/elf/rtld.c b/elf/rtld.c
index 2269dbe..c801ee5 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -99,6 +99,22 @@ uintptr_t __pointer_chk_guard_local
strong_alias (__pointer_chk_guard_local, __pointer_chk_guard)
#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 >= NAME_MAX || memchr (p, '/', len) != NULL)
+ return false;
+ }
+ return *p != '\0';
+}
/* List of auditing DSOs. */
static struct audit_list
@@ -718,6 +734,42 @@ 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[PATH_MAX];
+
+ while (*p != '\0')
+ {
+ /* Split preload list at space/colon. */
+ size_t len = strcspn (p, " :");
+ if (len > 0 && len < PATH_MAX)
+ {
+ memcpy (fname, p, len);
+ fname[len] = '\0';
+ }
+ else
+ fname[0] = '\0';
+
+ /* Skip over the substring and the following delimiter. */
+ p += len;
+ if (*p == ' ' || *p == ':')
+ ++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 +1516,8 @@ 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);