* [PATCH v3] dl-load: add memory barrier before updating the next [not found] <CGME20170403113000epcas5p37d569cf71eda2d413cfab5e7f7e3591d@epcas5p3.samsung.com> @ 2017-04-03 11:30 ` Maninder Singh 2017-04-03 11:45 ` Andreas Schwab 2017-04-03 13:25 ` Torvald Riegel 0 siblings, 2 replies; 3+ messages in thread From: Maninder Singh @ 2017-04-03 11:30 UTC (permalink / raw) To: libc-alpha, triegel, szabolcs.nagy Cc: pankaj.m, ajeet.y, a.sahrawat, lalit.mohan, akhilesh.k, hakbong5.lee, Maninder Singh, Vaneet Narang [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 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] dl-load: add memory barrier before updating the next 2017-04-03 11:30 ` [PATCH v3] dl-load: add memory barrier before updating the next Maninder Singh @ 2017-04-03 11:45 ` Andreas Schwab 2017-04-03 13:25 ` Torvald Riegel 1 sibling, 0 replies; 3+ messages in thread From: Andreas Schwab @ 2017-04-03 11:45 UTC (permalink / raw) To: Maninder Singh Cc: libc-alpha, triegel, szabolcs.nagy, pankaj.m, ajeet.y, a.sahrawat, lalit.mohan, akhilesh.k, hakbong5.lee, Vaneet Narang On Apr 03 2017, Maninder Singh <maninder1.s@samsung.com> wrote: > 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); Please remove the redundant parens. > 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)); Likewise. Andreas. -- Andreas Schwab, SUSE Labs, schwab@suse.de GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7 "And now for something completely different." ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] dl-load: add memory barrier before updating the next 2017-04-03 11:30 ` [PATCH v3] dl-load: add memory barrier before updating the next Maninder Singh 2017-04-03 11:45 ` Andreas Schwab @ 2017-04-03 13:25 ` Torvald Riegel 1 sibling, 0 replies; 3+ messages in thread From: Torvald Riegel @ 2017-04-03 13:25 UTC (permalink / raw) To: Maninder Singh Cc: libc-alpha, szabolcs.nagy, pankaj.m, ajeet.y, a.sahrawat, lalit.mohan, akhilesh.k, hakbong5.lee, Vaneet Narang On Mon, 2017-04-03 at 16:58 +0530, Maninder Singh wrote: > [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> Please address my comments on v2 of your patch too. ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-04-03 13:25 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <CGME20170403113000epcas5p37d569cf71eda2d413cfab5e7f7e3591d@epcas5p3.samsung.com> 2017-04-03 11:30 ` [PATCH v3] dl-load: add memory barrier before updating the next Maninder Singh 2017-04-03 11:45 ` Andreas Schwab 2017-04-03 13:25 ` Torvald Riegel
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