On Thu 06-02-20 15:28:12, Jan Kara wrote: > KASAN is reporting that __blk_add_trace() has a use-after-free issue > when accessing q->blk_trace. Indeed the switching of block tracing (and > thus eventual freeing of q->blk_trace) is completely unsynchronized with > the currently running tracing and thus it can happen that the blk_trace > structure is being freed just while __blk_add_trace() works on it. > Protect accesses to q->blk_trace by RCU during tracing and make sure we > wait for the end of RCU grace period when shutting down tracing. Luckily > that is rare enough event that we can afford that. Note that postponing > the freeing of blk_trace to an RCU callback should better be avoided as > it could have unexpected user visible side-effects as debugfs files > would be still existing for a short while block tracing has been shut > down. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=205711 > CC: stable@xxxxxxxxxxxxxxx > Reported-by: Tristan <tristmd@xxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Jens, do you plan to pick up the patch? Also the reporter asked me to update the reference as: Reported-by: Tristan Madani <tristmd@xxxxxxxxx> Should I resend the patch with this update & reviewed-by's or will you fix it up on commit? Thanks. Honza > --- > include/linux/blkdev.h | 2 +- > include/linux/blktrace_api.h | 18 +++++-- > kernel/trace/blktrace.c | 114 +++++++++++++++++++++++++++++++------------ > 3 files changed, 97 insertions(+), 37 deletions(-) > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index 4c636c42ad68..1cb5afed5515 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -524,7 +524,7 @@ struct request_queue { > unsigned int sg_reserved_size; > int node; > #ifdef CONFIG_BLK_DEV_IO_TRACE > - struct blk_trace *blk_trace; > + struct blk_trace __rcu *blk_trace; > struct mutex blk_trace_mutex; > #endif > /* > diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h > index 7bb2d8de9f30..3b6ff5902edc 100644 > --- a/include/linux/blktrace_api.h > +++ b/include/linux/blktrace_api.h > @@ -51,9 +51,13 @@ void __trace_note_message(struct blk_trace *, struct blkcg *blkcg, const char *f > **/ > #define blk_add_cgroup_trace_msg(q, cg, fmt, ...) \ > do { \ > - struct blk_trace *bt = (q)->blk_trace; \ > + struct blk_trace *bt; \ > + \ > + rcu_read_lock(); \ > + bt = rcu_dereference((q)->blk_trace); \ > if (unlikely(bt)) \ > __trace_note_message(bt, cg, fmt, ##__VA_ARGS__);\ > + rcu_read_unlock(); \ > } while (0) > #define blk_add_trace_msg(q, fmt, ...) \ > blk_add_cgroup_trace_msg(q, NULL, fmt, ##__VA_ARGS__) > @@ -61,10 +65,14 @@ void __trace_note_message(struct blk_trace *, struct blkcg *blkcg, const char *f > > static inline bool blk_trace_note_message_enabled(struct request_queue *q) > { > - struct blk_trace *bt = q->blk_trace; > - if (likely(!bt)) > - return false; > - return bt->act_mask & BLK_TC_NOTIFY; > + struct blk_trace *bt; > + bool ret; > + > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > + ret = bt && (bt->act_mask & BLK_TC_NOTIFY); > + rcu_read_unlock(); > + return ret; > } > > extern void blk_add_driver_data(struct request_queue *q, struct request *rq, > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > index 475e29498bca..a6d3016410eb 100644 > --- a/kernel/trace/blktrace.c > +++ b/kernel/trace/blktrace.c > @@ -335,6 +335,7 @@ static void put_probe_ref(void) > > static void blk_trace_cleanup(struct blk_trace *bt) > { > + synchronize_rcu(); > blk_trace_free(bt); > put_probe_ref(); > } > @@ -629,8 +630,10 @@ static int compat_blk_trace_setup(struct request_queue *q, char *name, > static int __blk_trace_startstop(struct request_queue *q, int start) > { > int ret; > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + bt = rcu_dereference_protected(q->blk_trace, > + lockdep_is_held(&q->blk_trace_mutex)); > if (bt == NULL) > return -EINVAL; > > @@ -740,8 +743,8 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) > void blk_trace_shutdown(struct request_queue *q) > { > mutex_lock(&q->blk_trace_mutex); > - > - if (q->blk_trace) { > + if (rcu_dereference_protected(q->blk_trace, > + lockdep_is_held(&q->blk_trace_mutex))) { > __blk_trace_startstop(q, 0); > __blk_trace_remove(q); > } > @@ -752,8 +755,10 @@ void blk_trace_shutdown(struct request_queue *q) > #ifdef CONFIG_BLK_CGROUP > static u64 blk_trace_bio_get_cgid(struct request_queue *q, struct bio *bio) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + /* We don't use the 'bt' value here except as an optimization... */ > + bt = rcu_dereference_protected(q->blk_trace, 1); > if (!bt || !(blk_tracer_flags.val & TRACE_BLK_OPT_CGROUP)) > return 0; > > @@ -796,10 +801,14 @@ blk_trace_request_get_cgid(struct request_queue *q, struct request *rq) > static void blk_add_trace_rq(struct request *rq, int error, > unsigned int nr_bytes, u32 what, u64 cgid) > { > - struct blk_trace *bt = rq->q->blk_trace; > + struct blk_trace *bt; > > - if (likely(!bt)) > + rcu_read_lock(); > + bt = rcu_dereference(rq->q->blk_trace); > + if (likely(!bt)) { > + rcu_read_unlock(); > return; > + } > > if (blk_rq_is_passthrough(rq)) > what |= BLK_TC_ACT(BLK_TC_PC); > @@ -808,6 +817,7 @@ static void blk_add_trace_rq(struct request *rq, int error, > > __blk_add_trace(bt, blk_rq_trace_sector(rq), nr_bytes, req_op(rq), > rq->cmd_flags, what, error, 0, NULL, cgid); > + rcu_read_unlock(); > } > > static void blk_add_trace_rq_insert(void *ignore, > @@ -853,14 +863,19 @@ static void blk_add_trace_rq_complete(void *ignore, struct request *rq, > static void blk_add_trace_bio(struct request_queue *q, struct bio *bio, > u32 what, int error) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > - if (likely(!bt)) > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > + if (likely(!bt)) { > + rcu_read_unlock(); > return; > + } > > __blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size, > bio_op(bio), bio->bi_opf, what, error, 0, NULL, > blk_trace_bio_get_cgid(q, bio)); > + rcu_read_unlock(); > } > > static void blk_add_trace_bio_bounce(void *ignore, > @@ -905,11 +920,14 @@ static void blk_add_trace_getrq(void *ignore, > if (bio) > blk_add_trace_bio(q, bio, BLK_TA_GETRQ, 0); > else { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > if (bt) > __blk_add_trace(bt, 0, 0, rw, 0, BLK_TA_GETRQ, 0, 0, > NULL, 0); > + rcu_read_unlock(); > } > } > > @@ -921,27 +939,35 @@ static void blk_add_trace_sleeprq(void *ignore, > if (bio) > blk_add_trace_bio(q, bio, BLK_TA_SLEEPRQ, 0); > else { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > if (bt) > __blk_add_trace(bt, 0, 0, rw, 0, BLK_TA_SLEEPRQ, > 0, 0, NULL, 0); > + rcu_read_unlock(); > } > } > > static void blk_add_trace_plug(void *ignore, struct request_queue *q) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > if (bt) > __blk_add_trace(bt, 0, 0, 0, 0, BLK_TA_PLUG, 0, 0, NULL, 0); > + rcu_read_unlock(); > } > > static void blk_add_trace_unplug(void *ignore, struct request_queue *q, > unsigned int depth, bool explicit) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > if (bt) { > __be64 rpdu = cpu_to_be64(depth); > u32 what; > @@ -953,14 +979,17 @@ static void blk_add_trace_unplug(void *ignore, struct request_queue *q, > > __blk_add_trace(bt, 0, 0, 0, 0, what, 0, sizeof(rpdu), &rpdu, 0); > } > + rcu_read_unlock(); > } > > static void blk_add_trace_split(void *ignore, > struct request_queue *q, struct bio *bio, > unsigned int pdu) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > if (bt) { > __be64 rpdu = cpu_to_be64(pdu); > > @@ -969,6 +998,7 @@ static void blk_add_trace_split(void *ignore, > BLK_TA_SPLIT, bio->bi_status, sizeof(rpdu), > &rpdu, blk_trace_bio_get_cgid(q, bio)); > } > + rcu_read_unlock(); > } > > /** > @@ -988,11 +1018,15 @@ static void blk_add_trace_bio_remap(void *ignore, > struct request_queue *q, struct bio *bio, > dev_t dev, sector_t from) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > struct blk_io_trace_remap r; > > - if (likely(!bt)) > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > + if (likely(!bt)) { > + rcu_read_unlock(); > return; > + } > > r.device_from = cpu_to_be32(dev); > r.device_to = cpu_to_be32(bio_dev(bio)); > @@ -1001,6 +1035,7 @@ static void blk_add_trace_bio_remap(void *ignore, > __blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size, > bio_op(bio), bio->bi_opf, BLK_TA_REMAP, bio->bi_status, > sizeof(r), &r, blk_trace_bio_get_cgid(q, bio)); > + rcu_read_unlock(); > } > > /** > @@ -1021,11 +1056,15 @@ static void blk_add_trace_rq_remap(void *ignore, > struct request *rq, dev_t dev, > sector_t from) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > struct blk_io_trace_remap r; > > - if (likely(!bt)) > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > + if (likely(!bt)) { > + rcu_read_unlock(); > return; > + } > > r.device_from = cpu_to_be32(dev); > r.device_to = cpu_to_be32(disk_devt(rq->rq_disk)); > @@ -1034,6 +1073,7 @@ static void blk_add_trace_rq_remap(void *ignore, > __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), > rq_data_dir(rq), 0, BLK_TA_REMAP, 0, > sizeof(r), &r, blk_trace_request_get_cgid(q, rq)); > + rcu_read_unlock(); > } > > /** > @@ -1051,14 +1091,19 @@ void blk_add_driver_data(struct request_queue *q, > struct request *rq, > void *data, size_t len) > { > - struct blk_trace *bt = q->blk_trace; > + struct blk_trace *bt; > > - if (likely(!bt)) > + rcu_read_lock(); > + bt = rcu_dereference(q->blk_trace); > + if (likely(!bt)) { > + rcu_read_unlock(); > return; > + } > > __blk_add_trace(bt, blk_rq_trace_sector(rq), blk_rq_bytes(rq), 0, 0, > BLK_TA_DRV_DATA, 0, len, data, > blk_trace_request_get_cgid(q, rq)); > + rcu_read_unlock(); > } > EXPORT_SYMBOL_GPL(blk_add_driver_data); > > @@ -1597,6 +1642,7 @@ static int blk_trace_remove_queue(struct request_queue *q) > return -EINVAL; > > put_probe_ref(); > + synchronize_rcu(); > blk_trace_free(bt); > return 0; > } > @@ -1758,6 +1804,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev, > struct hd_struct *p = dev_to_part(dev); > struct request_queue *q; > struct block_device *bdev; > + struct blk_trace *bt; > ssize_t ret = -ENXIO; > > bdev = bdget(part_devt(p)); > @@ -1770,21 +1817,23 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev, > > mutex_lock(&q->blk_trace_mutex); > > + bt = rcu_dereference_protected(q->blk_trace, > + lockdep_is_held(&q->blk_trace_mutex)); > if (attr == &dev_attr_enable) { > - ret = sprintf(buf, "%u\n", !!q->blk_trace); > + ret = sprintf(buf, "%u\n", !!bt); > goto out_unlock_bdev; > } > > - if (q->blk_trace == NULL) > + if (bt == NULL) > ret = sprintf(buf, "disabled\n"); > else if (attr == &dev_attr_act_mask) > - ret = blk_trace_mask2str(buf, q->blk_trace->act_mask); > + ret = blk_trace_mask2str(buf, bt->act_mask); > else if (attr == &dev_attr_pid) > - ret = sprintf(buf, "%u\n", q->blk_trace->pid); > + ret = sprintf(buf, "%u\n", bt->pid); > else if (attr == &dev_attr_start_lba) > - ret = sprintf(buf, "%llu\n", q->blk_trace->start_lba); > + ret = sprintf(buf, "%llu\n", bt->start_lba); > else if (attr == &dev_attr_end_lba) > - ret = sprintf(buf, "%llu\n", q->blk_trace->end_lba); > + ret = sprintf(buf, "%llu\n", bt->end_lba); > > out_unlock_bdev: > mutex_unlock(&q->blk_trace_mutex); > @@ -1801,6 +1850,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, > struct block_device *bdev; > struct request_queue *q; > struct hd_struct *p; > + struct blk_trace *bt; > u64 value; > ssize_t ret = -EINVAL; > > @@ -1831,8 +1881,10 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, > > mutex_lock(&q->blk_trace_mutex); > > + bt = rcu_dereference_protected(q->blk_trace, > + lockdep_is_held(&q->blk_trace_mutex)); > if (attr == &dev_attr_enable) { > - if (!!value == !!q->blk_trace) { > + if (!!value == !!bt) { > ret = 0; > goto out_unlock_bdev; > } > @@ -1844,18 +1896,18 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, > } > > ret = 0; > - if (q->blk_trace == NULL) > + if (bt == NULL) > ret = blk_trace_setup_queue(q, bdev); > > if (ret == 0) { > if (attr == &dev_attr_act_mask) > - q->blk_trace->act_mask = value; > + bt->act_mask = value; > else if (attr == &dev_attr_pid) > - q->blk_trace->pid = value; > + bt->pid = value; > else if (attr == &dev_attr_start_lba) > - q->blk_trace->start_lba = value; > + bt->start_lba = value; > else if (attr == &dev_attr_end_lba) > - q->blk_trace->end_lba = value; > + bt->end_lba = value; > } > > out_unlock_bdev: > -- > 2.16.4 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
