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authorFlorian Weimer <fweimer@redhat.com>2019-12-13 10:18:46 +0100
committerFlorian Weimer <fweimer@redhat.com>2019-12-13 10:18:46 +0100
commitf8ed116aa574435c6e28260f21963233682d3b57 (patch)
tree859f2077eec2bc1e19f99e4853c4a8bf1c2f7848 /include
parent365624e2d2a342cdb693b4cc35d2312169959e28 (diff)
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dlopen: Rework handling of pending NODELETE status
Commit a2e8aa0d9ea648068d8be52dd7b15f1b6a008e23 ("Block signals during the initial part of dlopen") was deemed necessary because of read-modify-write operations like the one in add_dependency in elf/dl-lookup.c. In the old code, we check for any kind of NODELETE status and bail out: /* Redo the NODELETE check, as when dl_load_lock wasn't held yet this could have changed. */ if (map->l_nodelete != link_map_nodelete_inactive) goto out; And then set pending status (during relocation): if (flags & DL_LOOKUP_FOR_RELOCATE) map->l_nodelete = link_map_nodelete_pending; else map->l_nodelete = link_map_nodelete_active; If a signal arrives during relocation and the signal handler, through lazy binding, adds a global scope dependency on the same map, it will set map->l_nodelete to link_map_nodelete_active. This will be overwritten with link_map_nodelete_pending by the dlopen relocation code. To avoid such problems in relation to the l_nodelete member, this commit introduces two flags for active NODELETE status (irrevocable) and pending NODELETE status (revocable until activate_nodelete is invoked). As a result, NODELETE processing in dlopen does not introduce further reasons why lazy binding from signal handlers is unsafe during dlopen, and a subsequent commit can remove signal blocking from dlopen. This does not address pre-existing issues (unrelated to the NODELETE changes) which make lazy binding in a signal handler during dlopen unsafe, such as the use of malloc in both cases. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/link.h31
1 files changed, 11 insertions, 20 deletions
diff --git a/include/link.h b/include/link.h
index 2e771e4..2acc836 100644
--- a/include/link.h
+++ b/include/link.h
@@ -79,22 +79,6 @@ struct r_search_path_struct
int malloced;
};
-/* Type used by the l_nodelete member. */
-enum link_map_nodelete
-{
- /* This link map can be deallocated. */
- link_map_nodelete_inactive = 0, /* Zero-initialized in _dl_new_object. */
-
- /* This link map cannot be deallocated. */
- link_map_nodelete_active,
-
- /* This link map cannot be deallocated after dlopen has succeded.
- dlopen turns this into link_map_nodelete_active. dlclose treats
- this intermediate state as link_map_nodelete_active. */
- link_map_nodelete_pending,
-};
-
-
/* Structure describing a loaded shared object. The `l_next' and `l_prev'
members form a chain of all the shared objects loaded at startup.
@@ -218,10 +202,17 @@ struct link_map
freed, ie. not allocated with
the dummy malloc in ld.so. */
- /* Actually of type enum link_map_nodelete. Separate byte due to
- a read in add_dependency in elf/dl-lookup.c outside the loader
- lock. Only valid for l_type == lt_loaded. */
- unsigned char l_nodelete;
+ /* NODELETE status of the map. Only valid for maps of type
+ lt_loaded. Lazy binding sets l_nodelete_active directly,
+ potentially from signal handlers. Initial loading of an
+ DF_1_NODELETE object set l_nodelete_pending. Relocation may
+ set l_nodelete_pending as well. l_nodelete_pending maps are
+ promoted to l_nodelete_active status in the final stages of
+ dlopen, prior to calling ELF constructors. dlclose only
+ refuses to unload l_nodelete_active maps, the pending status is
+ ignored. */
+ bool l_nodelete_active;
+ bool l_nodelete_pending;
#include <link_map.h>