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
This commit is contained in:
Mark Johnston 2016-12-22 17:37:39 +00:00
parent ca7af67ac9
commit c02741759f
Notes: svn2git 2020-12-20 02:59:44 +00:00
svn path=/head/; revision=310420
2 changed files with 50 additions and 5 deletions

View File

@ -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 *, Obj_Entry *, Obj_Entry *);
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_Entry *root, RtldLockState *lockstate)
* 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_Entry *root, RtldLockState *lockstate)
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, RtldLockState *lockstate)
* 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, RtldLockState *lockstate)
}
}
wlock_acquire(rtld_bind_lock, lockstate);
unhold_object(elm->obj);
}
errmsg_restore(saved_msg);
}
@ -3553,11 +3577,13 @@ dl_iterate_phdr(__dl_iterate_hdr_callback callback, void *param)
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);
}
}

View File

@ -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 (%) */