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[PATCH v3] dl-load: add memory barrier before updating the next
- From: Maninder Singh <maninder1 dot s at samsung dot com>
- To: libc-alpha at sourceware dot org, triegel at redhat dot com, szabolcs dot nagy at arm dot com
- Cc: pankaj dot m at samsung dot com, ajeet dot y at samsung dot com, a dot sahrawat at samsung dot com, lalit dot mohan at samsung dot com, akhilesh dot k at samsung dot com, hakbong5 dot lee at samsung dot com, Maninder Singh <maninder1 dot s at samsung dot com>, Vaneet Narang <v dot narang at samsung dot com>
- Date: Mon, 3 Apr 2017 16:58:45 +0530
- Subject: [PATCH v3] dl-load: add memory barrier before updating the next
- Authentication-results: sourceware.org; auth=none
- Cms-type: 105P
- Dlp-filter: Pass
- References: <CGME20170403113000epcas5p37d569cf71eda2d413cfab5e7f7e3591d@epcas5p3.samsung.com>
[BZ #21349]: race condition between dl_open and rtld lazy symbol resolve.
This patch adds C11 memory barrier before updating the liblist next.
Issue Fix: race condition between add_name_to_object & _dl_name_match_p.
One threads calling dlopen which further calls add_name_to_object &
other thread trying to resolve RTLD_LAZY symbols through
_dl_runtime_resolve which further calls.
_dl_name_match_p checks if libname->next is valid, then it assumes
libname->next->name to be valid. Also add_name_to_object initialized
name first and then sets valid next pointer.
This patch avoids any reorder of instruction when next is set before
name to avoid any race.
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
---
v1 -> v2: use C11 atomics rather than direct memory barriers.
v2 -> v3: use comments for barriers and enter Bugzilla ID.
elf/dl-load.c | 5 ++++-
elf/dl-misc.c | 5 ++++-
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/elf/dl-load.c b/elf/dl-load.c
index a5318f9..03c6afb 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -418,7 +418,10 @@ add_name_to_object (struct link_map *l, const char *name)
newname->name = memcpy (newname + 1, name, name_len);
newname->next = NULL;
newname->dont_free = 0;
- lastp->next = newname;
+ /* We need release memory order here because we need to synchronize
+ with other thread doing _dl_runtime_resolve which calls _dl_name_match_p
+ to traverse all names added to libname_list*/
+ atomic_store_release (&(lastp->next), newname);
}
/* Standard search directories. */
diff --git a/elf/dl-misc.c b/elf/dl-misc.c
index 1e9a6ee..a26d6f6 100644
--- a/elf/dl-misc.c
+++ b/elf/dl-misc.c
@@ -295,7 +295,10 @@ _dl_name_match_p (const char *name, const struct link_map *map)
if (strcmp (name, runp->name) == 0)
return 1;
else
- runp = runp->next;
+ /* We need to acquire memory order here because we need to synchronize
+ with other thread calling dlopen and adding new name to libname_list
+ through add_name_to_object */
+ runp = atomic_load_acquire(&(runp->next));
return 0;
}
--
1.7.1