[PATCH 3.16 212/245] blktrace: Protect q->blk_trace with RCU

3.16.83-rc1 review patch. If anyone has any objections, please let me know.

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From: Jan Kara jack@suse.cz

commit c780e86dd48ef6467a1146cf7d0fe1e05a635039 upstream.

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 Reviewed-by: Chaitanya Kulkarni chaitanya.kulkarni@wdc.com Reviewed-by: Ming Lei ming.lei@redhat.com Tested-by: Ming Lei ming.lei@redhat.com Reviewed-by: Bart Van Assche bvanassche@acm.org Reported-by: Tristan Madani tristmd@gmail.com Signed-off-by: Jan Kara jack@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk [bwh: Backported to 3.16: - Drop changes in blk_trace_note_message_enabled(), blk_trace_bio_get_cgid() - Adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -447,7 +447,7 @@ 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 /* --- a/include/linux/blktrace_api.h +++ b/include/linux/blktrace_api.h @@ -51,9 +51,13 @@ void __trace_note_message(struct blk_tra **/ #define blk_add_trace_msg(q, 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, fmt, ##__VA_ARGS__); \ + rcu_read_unlock(); \ } while (0) #define BLK_TN_MAX_MSG 128

--- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -302,6 +302,7 @@ static void blk_trace_free(struct blk_tr

static void blk_trace_cleanup(struct blk_trace *bt) { + synchronize_rcu(); blk_trace_free(bt); if (atomic_dec_and_test(&blk_probes_ref)) blk_unregister_tracepoints(); @@ -616,8 +617,10 @@ static int compat_blk_trace_setup(struct 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;

@@ -726,8 +729,8 @@ int blk_trace_ioctl(struct block_device 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); } @@ -753,10 +756,14 @@ void blk_trace_shutdown(struct request_q static void blk_add_trace_rq(struct request_queue *q, struct request *rq, unsigned int nr_bytes, u32 what) { - 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; + }

if (rq->cmd_type == REQ_TYPE_BLOCK_PC) { what |= BLK_TC_ACT(BLK_TC_PC); @@ -767,6 +774,7 @@ static void blk_add_trace_rq(struct requ __blk_add_trace(bt, blk_rq_pos(rq), nr_bytes, rq->cmd_flags, what, rq->errors, 0, NULL); } + rcu_read_unlock(); }

static void blk_add_trace_rq_abort(void *ignore, @@ -816,16 +824,21 @@ static void blk_add_trace_rq_complete(vo 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; + }

if (!error && !bio_flagged(bio, BIO_UPTODATE)) error = EIO;

__blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size, bio->bi_rw, what, error, 0, NULL); + rcu_read_unlock(); }

static void blk_add_trace_bio_bounce(void *ignore, @@ -870,10 +883,13 @@ static void blk_add_trace_getrq(void *ig 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, BLK_TA_GETRQ, 0, 0, NULL); + rcu_read_unlock(); } }

@@ -885,27 +901,35 @@ static void blk_add_trace_sleeprq(void * 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, BLK_TA_SLEEPRQ, 0, 0, NULL); + 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, BLK_TA_PLUG, 0, 0, NULL); + 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; @@ -917,14 +941,17 @@ static void blk_add_trace_unplug(void *i

__blk_add_trace(bt, 0, 0, 0, what, 0, sizeof(rpdu), &rpdu); } + 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);

@@ -933,6 +960,7 @@ static void blk_add_trace_split(void *ig !bio_flagged(bio, BIO_UPTODATE), sizeof(rpdu), &rpdu); } + rcu_read_unlock(); }

/** @@ -952,11 +980,15 @@ static void blk_add_trace_bio_remap(void 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->bi_bdev->bd_dev); @@ -965,6 +997,7 @@ static void blk_add_trace_bio_remap(void __blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size, bio->bi_rw, BLK_TA_REMAP, !bio_flagged(bio, BIO_UPTODATE), sizeof(r), &r); + rcu_read_unlock(); }

/** @@ -985,11 +1018,15 @@ static void blk_add_trace_rq_remap(void 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)); @@ -998,6 +1035,7 @@ static void blk_add_trace_rq_remap(void __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), rq_data_dir(rq), BLK_TA_REMAP, !!rq->errors, sizeof(r), &r); + rcu_read_unlock(); }

/** @@ -1015,10 +1053,14 @@ void blk_add_driver_data(struct request_ 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; + }

if (rq->cmd_type == REQ_TYPE_BLOCK_PC) __blk_add_trace(bt, 0, blk_rq_bytes(rq), 0, @@ -1026,6 +1068,7 @@ void blk_add_driver_data(struct request_ else __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), 0, BLK_TA_DRV_DATA, rq->errors, len, data); + rcu_read_unlock(); } EXPORT_SYMBOL_GPL(blk_add_driver_data);

@@ -1537,6 +1580,7 @@ static int blk_trace_remove_queue(struct spin_lock_irq(&running_trace_lock); list_del(&bt->running_list); spin_unlock_irq(&running_trace_lock); + synchronize_rcu(); blk_trace_free(bt); return 0; } @@ -1698,6 +1742,7 @@ static ssize_t sysfs_blk_trace_attr_show 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)); @@ -1710,21 +1755,23 @@ static ssize_t sysfs_blk_trace_attr_show

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); @@ -1741,6 +1788,7 @@ static ssize_t sysfs_blk_trace_attr_stor struct block_device *bdev; struct request_queue *q; struct hd_struct *p; + struct blk_trace *bt; u64 value; ssize_t ret = -EINVAL;

@@ -1771,8 +1819,10 @@ static ssize_t sysfs_blk_trace_attr_stor

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; } @@ -1784,18 +1834,18 @@ static ssize_t sysfs_blk_trace_attr_stor }

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: