svn commit: r310420 - head/libexec/rtld-elf
Mark Johnston
markj at FreeBSD.org
Thu Dec 22 17:37:41 UTC 2016
Author: markj
Date: Thu Dec 22 17:37:39 2016
New Revision: 310420
URL: https://svnweb.freebsd.org/changeset/base/310420
Log:
rtld: Fix a race between dl_iterate_phdr() and dlclose().
Add a transient reference count to ensure that the phdr argument to the
callback remains valid while the bind lock is dropped.
Reviewed by: kib
MFC after: 2 weeks
Sponsored by: Dell EMC Isilon
Modified:
head/libexec/rtld-elf/rtld.c
head/libexec/rtld-elf/rtld.h
Modified: head/libexec/rtld-elf/rtld.c
==============================================================================
--- head/libexec/rtld-elf/rtld.c Thu Dec 22 16:19:05 2016 (r310419)
+++ head/libexec/rtld-elf/rtld.c Thu Dec 22 17:37:39 2016 (r310420)
@@ -87,6 +87,8 @@ static char *errmsg_save(void);
static void *fill_search_info(const char *, size_t, void *);
static char *find_library(const char *, const Obj_Entry *, int *);
static const char *gethints(bool);
+static void hold_object(Obj_Entry *);
+static void unhold_object(Obj_Entry *);
static void init_dag(Obj_Entry *);
static void init_pagesizes(Elf_Auxinfo **aux_info);
static void init_rtld(caddr_t, Elf_Auxinfo **);
@@ -112,6 +114,7 @@ static void objlist_put_after(Objlist *,
static void objlist_remove(Objlist *, Obj_Entry *);
static int parse_libdir(const char *);
static void *path_enumerate(const char *, path_enum_proc, void *);
+static void release_object(Obj_Entry *);
static int relocate_object_dag(Obj_Entry *root, bool bind_now,
Obj_Entry *rtldobj, int flags, RtldLockState *lockstate);
static int relocate_object(Obj_Entry *obj, bool bind_now, Obj_Entry *rtldobj,
@@ -1852,6 +1855,23 @@ globallist_next(const Obj_Entry *obj)
}
}
+/* Prevent the object from being unmapped while the bind lock is dropped. */
+static void
+hold_object(Obj_Entry *obj)
+{
+
+ obj->holdcount++;
+}
+
+static void
+unhold_object(Obj_Entry *obj)
+{
+
+ assert(obj->holdcount > 0);
+ if (--obj->holdcount == 0 && obj->unholdfree)
+ release_object(obj);
+}
+
static void
process_z(Obj_Entry *root)
{
@@ -2417,6 +2437,7 @@ objlist_call_fini(Objlist *list, Obj_Ent
* won't be unloaded although its fini function has been
* called.
*/
+ hold_object(elm->obj);
lock_release(rtld_bind_lock, lockstate);
/*
@@ -2444,6 +2465,7 @@ objlist_call_fini(Objlist *list, Obj_Ent
call_initfini_pointer(elm->obj, elm->obj->fini);
}
wlock_acquire(rtld_bind_lock, lockstate);
+ unhold_object(elm->obj);
/* No need to free anything if process is going down. */
if (root != NULL)
free(elm);
@@ -2497,6 +2519,7 @@ objlist_call_init(Objlist *list, RtldLoc
* without better locking.
*/
elm->obj->init_done = true;
+ hold_object(elm->obj);
lock_release(rtld_bind_lock, lockstate);
/*
@@ -2523,6 +2546,7 @@ objlist_call_init(Objlist *list, RtldLoc
}
}
wlock_acquire(rtld_bind_lock, lockstate);
+ unhold_object(elm->obj);
}
errmsg_restore(saved_msg);
}
@@ -3553,11 +3577,13 @@ dl_iterate_phdr(__dl_iterate_hdr_callbac
for (obj = globallist_curr(TAILQ_FIRST(&obj_list)); obj != NULL;) {
TAILQ_INSERT_AFTER(&obj_list, obj, &marker, next);
rtld_fill_dl_phdr_info(obj, &phdr_info);
+ hold_object(obj);
lock_release(rtld_bind_lock, &bind_lockstate);
error = callback(&phdr_info, sizeof phdr_info, param);
wlock_acquire(rtld_bind_lock, &bind_lockstate);
+ unhold_object(obj);
obj = globallist_next(&marker);
TAILQ_REMOVE(&obj_list, &marker, next);
if (error != 0) {
@@ -3812,6 +3838,19 @@ _r_debug_postinit(struct link_map *m)
__compiler_membar();
}
+static void
+release_object(Obj_Entry *obj)
+{
+
+ if (obj->holdcount > 0) {
+ obj->unholdfree = true;
+ return;
+ }
+ munmap(obj->mapbase, obj->mapsize);
+ linkmap_delete(obj);
+ obj_free(obj);
+}
+
/*
* Get address of the pointer variable in the main program.
* Prefer non-weak symbol over the weak one.
@@ -4399,12 +4438,16 @@ unload_object(Obj_Entry *root)
LD_UTRACE(UTRACE_UNLOAD_OBJECT, obj, obj->mapbase,
obj->mapsize, 0, obj->path);
dbg("unloading \"%s\"", obj->path);
- unload_filtees(root);
- munmap(obj->mapbase, obj->mapsize);
- linkmap_delete(obj);
+ /*
+ * Unlink the object now to prevent new references from
+ * being acquired while the bind lock is dropped in
+ * recursive dlclose() invocations.
+ */
TAILQ_REMOVE(&obj_list, obj, next);
obj_count--;
- obj_free(obj);
+
+ unload_filtees(root);
+ release_object(obj);
}
}
Modified: head/libexec/rtld-elf/rtld.h
==============================================================================
--- head/libexec/rtld-elf/rtld.h Thu Dec 22 16:19:05 2016 (r310419)
+++ head/libexec/rtld-elf/rtld.h Thu Dec 22 17:37:39 2016 (r310420)
@@ -142,7 +142,8 @@ typedef struct Struct_Obj_Entry {
TAILQ_ENTRY(Struct_Obj_Entry) next;
char *path; /* Pathname of underlying file (%) */
char *origin_path; /* Directory path of origin file */
- int refcount;
+ int refcount; /* DAG references */
+ int holdcount; /* Count of transient references */
int dl_refcount; /* Number of times loaded by dlopen */
/* These items are computed by map_object() or by digest_phdr(). */
@@ -265,6 +266,7 @@ typedef struct Struct_Obj_Entry {
bool valid_hash_gnu : 1; /* A valid GNU hash tag is available */
bool dlopened : 1; /* dlopen()-ed (vs. load statically) */
bool marker : 1; /* marker on the global obj list */
+ bool unholdfree : 1; /* unmap upon last unhold */
struct link_map linkmap; /* For GDB and dlinfo() */
Objlist dldags; /* Object belongs to these dlopened DAGs (%) */
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