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Avoid late failure in dlopen in global scope update [BZ #25112]

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The call to add_to_global in dl_open_worker happens after running ELF
constructors for new objects.  At this point, proper recovery from
malloc failure would be quite complicated: We would have to run the
ELF destructors and close all opened objects, something that we
currently do not do.

Instead, this change splits add_to_global into two phases,
add_to_global_resize (which can raise an exception, called before ELF
constructors run), and add_to_global_update (which cannot, called
after ELF constructors).  A complication arises due to recursive
dlopen: After the inner dlopen consumes some space, the pre-allocation
in the outer dlopen may no longer be sufficient.  A new member in the
namespace structure, _ns_global_scope_pending_adds keeps track of the
maximum number of objects that need to be added to the global scope.
This enables the inner add_to_global_resize call to take into account
the needs of an outer dlopen.

Most code in the dynamic linker assumes that the number of global
scope entries fits into an unsigned int (matching the r_nlist member
of struct r_scop_elem).  Therefore, change the type of
_ns_global_scope_alloc to unsigned int (from size_t), and add overflow
checks.

Change-Id: Ie08e2f318510d5a6a4bcb1c315f46791b5b77524
This commit is contained in:
Florian Weimer 2019-10-31 18:25:39 +01:00
parent 79e0cd7b3c
commit 440b7f8653
2 changed files with 117 additions and 52 deletions
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160
elf/dl-open.c
View File

@ -50,22 +50,38 @@ struct dl_open_args
struct link_map *map;
/* Namespace ID. */
Lmid_t nsid;
/* Original value of _ns_global_scope_pending_adds. Set by
dl_open_worker. Only valid if nsid is a real namespace
(non-negative). */
unsigned int original_global_scope_pending_adds;
/* Original parameters to the program and the current environment. */
int argc;
char **argv;
char **env;
};
static int
add_to_global (struct link_map *new)
/* Called in case the global scope cannot be extended. */
static void __attribute__ ((noreturn))
add_to_global_resize_failure (struct link_map *new)
{
struct link_map **new_global;
unsigned int to_add = 0;
unsigned int cnt;
_dl_signal_error (ENOMEM, new->l_libname->name, NULL,
N_ ("cannot extend global scope"));
}
/* Grow the global scope array for the namespace, so that all the new
global objects can be added later in add_to_global_update, without
risk of memory allocation failure. add_to_global_resize raises
exceptions for memory allocation errors. */
static void
add_to_global_resize (struct link_map *new)
{
struct link_namespaces *ns = &GL (dl_ns)[new->l_ns];
/* Count the objects we have to put in the global scope. */
for (cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
unsigned int to_add = 0;
for (unsigned int cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
if (new->l_searchlist.r_list[cnt]->l_global == 0)
++to_add;
@ -83,47 +99,51 @@ add_to_global (struct link_map *new)
in an realloc() call. Therefore we allocate a completely new
array the first time we have to add something to the locale scope. */
struct link_namespaces *ns = &GL(dl_ns)[new->l_ns];
if (__builtin_add_overflow (ns->_ns_global_scope_pending_adds, to_add,
&ns->_ns_global_scope_pending_adds))
add_to_global_resize_failure (new);
unsigned int new_size = 0; /* 0 means no new allocation. */
void *old_global = NULL; /* Old allocation if free-able. */
/* Minimum required element count for resizing. Adjusted below for
an exponential resizing policy. */
size_t required_new_size;
if (__builtin_add_overflow (ns->_ns_main_searchlist->r_nlist,
ns->_ns_global_scope_pending_adds,
&required_new_size))
add_to_global_resize_failure (new);
if (ns->_ns_global_scope_alloc == 0)
{
/* This is the first dynamic object given global scope. */
ns->_ns_global_scope_alloc
= ns->_ns_main_searchlist->r_nlist + to_add + 8;
new_global = (struct link_map **)
malloc (ns->_ns_global_scope_alloc * sizeof (struct link_map *));
if (__builtin_add_overflow (required_new_size, 8, &new_size))
add_to_global_resize_failure (new);
}
else if (required_new_size > ns->_ns_global_scope_alloc)
{
if (__builtin_mul_overflow (required_new_size, 2, &new_size))
add_to_global_resize_failure (new);
/* The old array was allocated with our malloc, not the minimal
malloc. */
old_global = ns->_ns_main_searchlist->r_list;
}
if (new_size > 0)
{
size_t allocation_size;
if (__builtin_mul_overflow (new_size, sizeof (struct link_map *),
&allocation_size))
add_to_global_resize_failure (new);
struct link_map **new_global = malloc (allocation_size);
if (new_global == NULL)
{
ns->_ns_global_scope_alloc = 0;
nomem:
_dl_signal_error (ENOMEM, new->l_libname->name, NULL,
N_("cannot extend global scope"));
return 1;
}
add_to_global_resize_failure (new);
/* Copy over the old entries. */
ns->_ns_main_searchlist->r_list
= memcpy (new_global, ns->_ns_main_searchlist->r_list,
(ns->_ns_main_searchlist->r_nlist
* sizeof (struct link_map *)));
}
else if (ns->_ns_main_searchlist->r_nlist + to_add
> ns->_ns_global_scope_alloc)
{
/* We have to extend the existing array of link maps in the
main map. */
struct link_map **old_global
= GL(dl_ns)[new->l_ns]._ns_main_searchlist->r_list;
size_t new_nalloc = ((ns->_ns_global_scope_alloc + to_add) * 2);
memcpy (new_global, ns->_ns_main_searchlist->r_list,
ns->_ns_main_searchlist->r_nlist * sizeof (struct link_map *));
new_global = (struct link_map **)
malloc (new_nalloc * sizeof (struct link_map *));
if (new_global == NULL)
goto nomem;
memcpy (new_global, old_global,
ns->_ns_global_scope_alloc * sizeof (struct link_map *));
ns->_ns_global_scope_alloc = new_nalloc;
ns->_ns_global_scope_alloc = new_size;
ns->_ns_main_searchlist->r_list = new_global;
if (!RTLD_SINGLE_THREAD_P)
@ -131,16 +151,28 @@ add_to_global (struct link_map *new)
free (old_global);
}
}
/* Actually add the new global objects to the global scope. Must be
called after add_to_global_resize. This function cannot fail. */
static void
add_to_global_update (struct link_map *new)
{
struct link_namespaces *ns = &GL (dl_ns)[new->l_ns];
/* Now add the new entries. */
unsigned int new_nlist = ns->_ns_main_searchlist->r_nlist;
for (cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
for (unsigned int cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
{
struct link_map *map = new->l_searchlist.r_list[cnt];
if (map->l_global == 0)
{
map->l_global = 1;
/* The array has been resized by add_to_global_resize. */
assert (new_nlist < ns->_ns_global_scope_alloc);
ns->_ns_main_searchlist->r_list[new_nlist++] = map;
/* We modify the global scope. Report this. */
@ -149,10 +181,15 @@ add_to_global (struct link_map *new)
map->l_name, map->l_ns);
}
}
/* Some of the pending adds have been performed by the loop above.
Adjust the counter accordingly. */
unsigned int added = new_nlist - ns->_ns_main_searchlist->r_nlist;
assert (added <= ns->_ns_global_scope_pending_adds);
ns->_ns_global_scope_pending_adds -= added;
atomic_write_barrier ();
ns->_ns_main_searchlist->r_nlist = new_nlist;
return 0;
}
/* Search link maps in all namespaces for the DSO that contains the object at
@ -225,6 +262,10 @@ dl_open_worker (void *a)
args->nsid = call_map->l_ns;
}
/* Retain the old value, so that it can be restored. */
args->original_global_scope_pending_adds
= GL (dl_ns)[args->nsid]._ns_global_scope_pending_adds;
/* One might be tempted to assert that we are RT_CONSISTENT at this point, but that
may not be true if this is a recursive call to dlopen. */
_dl_debug_initialize (0, args->nsid);
@ -266,7 +307,10 @@ dl_open_worker (void *a)
/* If the user requested the object to be in the global namespace
but it is not so far, add it now. */
if ((mode & RTLD_GLOBAL) && new->l_global == 0)
(void) add_to_global (new);
{
add_to_global_resize (new);
add_to_global_update (new);
}
assert (_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT);
@ -526,6 +570,11 @@ TLS generation counter wrapped! Please report this."));
DL_STATIC_INIT (new);
#endif
/* Perform the necessary allocations for adding new global objects
to the global scope below, via add_to_global_update. */
if (mode & RTLD_GLOBAL)
add_to_global_resize (new);
/* Run the initializer functions of new objects. Temporarily
disable the exception handler, so that lazy binding failures are
fatal. */
@ -542,10 +591,7 @@ TLS generation counter wrapped! Please report this."));
/* Now we can make the new map available in the global scope. */
if (mode & RTLD_GLOBAL)
/* Move the object in the global namespace. */
if (add_to_global (new) != 0)
/* It failed. */
return;
add_to_global_update (new);
#ifndef SHARED
/* We must be the static _dl_open in libc.a. A static program that
@ -559,7 +605,6 @@ TLS generation counter wrapped! Please report this."));
new->l_name, new->l_ns, new->l_direct_opencount);
}
void *
_dl_open (const char *file, int mode, const void *caller_dlopen, Lmid_t nsid,
int argc, char *argv[], char *env[])
@ -627,6 +672,19 @@ no more namespaces available for dlmopen()"));
_dl_unload_cache ();
#endif
/* Do this for both the error and success cases. The old value has
only been determined if the namespace ID was assigned (i.e., it
is not __LM_ID_CALLER). In the success case, we actually may
have consumed more pending adds than planned (because the local
scopes overlap in case of a recursive dlopen, the inner dlopen
doing some of the globalization work of the outer dlopen), so the
old pending adds value is larger than absolutely necessary.
Since it is just a conservative upper bound, this is harmless.
The top-level dlopen call will restore the field to zero. */
if (args.nsid >= 0)
GL (dl_ns)[args.nsid]._ns_global_scope_pending_adds
= args.original_global_scope_pending_adds;
/* See if an error occurred during loading. */
if (__glibc_unlikely (exception.errstring != NULL))
{

9
sysdeps/generic/ldsodefs.h
View File

@ -328,7 +328,14 @@ struct rtld_global
/* This is zero at program start to signal that the global scope map is
allocated by rtld. Later it keeps the size of the map. It might be
reset if in _dl_close if the last global object is removed. */
size_t _ns_global_scope_alloc;
unsigned int _ns_global_scope_alloc;
/* During dlopen, this is the number of objects that still need to
be added to the global scope map. It has to be taken into
account when resizing the map, for future map additions after
recursive dlopen calls from ELF constructors. */
unsigned int _ns_global_scope_pending_adds;
/* Search table for unique objects. */
struct unique_sym_table
{