From: Maninder Singh <maninder1.s@samsung.com>
To: libc-alpha@sourceware.org, triegel@redhat.com, szabolcs.nagy@arm.com
Cc: pankaj.m@samsung.com, ajeet.y@samsung.com,
a.sahrawat@samsung.com, lalit.mohan@samsung.com,
akhilesh.k@samsung.com, hakbong5.lee@samsung.com,
Maninder Singh <maninder1.s@samsung.com>,
Vaneet Narang <v.narang@samsung.com>
Subject: [PATCH v3] dl-load: add memory barrier before updating the next
Date: Mon, 03 Apr 2017 11:30:00 -0000 [thread overview]
Message-ID: <1491218925-19517-1-git-send-email-maninder1.s@samsung.com> (raw)
In-Reply-To: <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
next parent reply other threads:[~2017-04-03 11:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20170403113000epcas5p37d569cf71eda2d413cfab5e7f7e3591d@epcas5p3.samsung.com>
2017-04-03 11:30 ` Maninder Singh [this message]
2017-04-03 11:45 ` Andreas Schwab
2017-04-03 13:25 ` Torvald Riegel
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