From d8e47bd066d7e626f9f45d416182d585b7e18b9b Mon Sep 17 00:00:00 2001 From: David Matlack Date: Thu, 23 Apr 2026 17:40:29 +0000 Subject: [PATCH] liveupdate: Reference count incoming FLB data Increment the incoming FLB refcount in liveupdate_flb_get_incoming() so that the FLB structure cannot be freed while the caller is actively using it. Add an additional liveupdate_flb_put_incoming() function so the caller can explicitly indicate when it is done using the FLB data. During a Live Update, a subsystem might need to hold onto the incoming File-Lifecycle-Bound (FLB) data for an extended period, such as during device enumeration. Incrementing the reference count guarantees that the data remains valid and accessible until the subsystem releases it, preventing future use-after-free bugs. Fixes: cab056f2aae7 ("liveupdate: luo_flb: introduce File-Lifecycle-Bound global state") Signed-off-by: David Matlack Reviewed-by: Samiullah Khawaja Reviewed-by: Pasha Tatashin Link: https://lore.kernel.org/r/20260423174032.3140399-3-dmatlack@google.com Signed-off-by: Pasha Tatashin Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/liveupdate.h | 6 ++++++ kernel/liveupdate/luo_flb.c | 32 +++++++++++++++++--------------- lib/tests/liveupdate.c | 3 +++ 3 files changed, 26 insertions(+), 15 deletions(-) diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h index 8d3bbc35c828..88722e5caf02 100644 --- a/include/linux/liveupdate.h +++ b/include/linux/liveupdate.h @@ -240,6 +240,8 @@ void liveupdate_unregister_flb(struct liveupdate_file_handler *fh, struct liveupdate_flb *flb); int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp); +void liveupdate_flb_put_incoming(struct liveupdate_flb *flb); + int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp); #else /* CONFIG_LIVEUPDATE */ @@ -280,6 +282,10 @@ static inline int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, return -EOPNOTSUPP; } +static inline void liveupdate_flb_put_incoming(struct liveupdate_flb *flb) +{ +} + static inline int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp) { diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c index 59c5f31ab767..8f5c5dd01cd0 100644 --- a/kernel/liveupdate/luo_flb.c +++ b/kernel/liveupdate/luo_flb.c @@ -165,7 +165,7 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb) bool found = false; int err; - guard(mutex)(&private->incoming.lock); + lockdep_assert_held(&private->incoming.lock); if (private->incoming.finished) return -ENODATA; @@ -206,12 +206,14 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb) return 0; } -static void luo_flb_file_finish_one(struct liveupdate_flb *flb) +void liveupdate_flb_put_incoming(struct liveupdate_flb *flb) { struct luo_flb_private *private = luo_flb_get_private(flb); + struct liveupdate_flb_op_args args = {0}; - if (refcount_dec_and_test(&private->incoming.count)) { - struct liveupdate_flb_op_args args = {0}; + scoped_guard(mutex, &private->incoming.lock) { + if (!refcount_dec_and_test(&private->incoming.count)) + return; if (!private->incoming.retrieved) { int err = luo_flb_retrieve_one(flb); @@ -220,16 +222,14 @@ static void luo_flb_file_finish_one(struct liveupdate_flb *flb) return; } - scoped_guard(mutex, &private->incoming.lock) { - args.flb = flb; - args.obj = private->incoming.obj; - flb->ops->finish(&args); + args.flb = flb; + args.obj = private->incoming.obj; + flb->ops->finish(&args); - private->incoming.data = 0; - private->incoming.obj = NULL; - private->incoming.finished = true; - module_put(flb->ops->owner); - } + private->incoming.data = 0; + private->incoming.obj = NULL; + private->incoming.finished = true; + module_put(flb->ops->owner); } } @@ -312,7 +312,7 @@ void luo_flb_file_finish(struct liveupdate_file_handler *fh) guard(rwsem_read)(&luo_register_rwlock); list_for_each_entry_reverse(iter, flb_list, list) - luo_flb_file_finish_one(iter->flb); + liveupdate_flb_put_incoming(iter->flb); } static void luo_flb_unregister_one(struct liveupdate_file_handler *fh, @@ -509,6 +509,8 @@ int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp) if (!liveupdate_enabled()) return -EOPNOTSUPP; + guard(mutex)(&private->incoming.lock); + if (!private->incoming.obj) { int err = luo_flb_retrieve_one(flb); @@ -516,7 +518,7 @@ int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp) return err; } - guard(mutex)(&private->incoming.lock); + refcount_inc(&private->incoming.count); *objp = private->incoming.obj; return 0; diff --git a/lib/tests/liveupdate.c b/lib/tests/liveupdate.c index e4b0ecbee32f..4c08a7c6fb78 100644 --- a/lib/tests/liveupdate.c +++ b/lib/tests/liveupdate.c @@ -105,6 +105,9 @@ static void liveupdate_test_init(void) pr_err("liveupdate_flb_get_incoming for %s failed: %pe\n", flb->compatible, ERR_PTR(err)); } + + if (!err) + liveupdate_flb_put_incoming(flb); } initialized = true; }