Ah, this patch also requires another follow-on fix:
>
> commit e791ce27c3f6a1d3c746fd6a8f8e36c9540ec6f9
> Author: Hannes Reinecke <hare@xxxxxxx>
> Date: Mon Apr 24 10:26:36 2017 +0200
>
> scsi: sg: reset 'res_in_use' after unlinking reserved array
>
>
> On Tue, Aug 15, 2017 at 8:09 PM, Todd Poynor <toddpoynor@xxxxxxxxxx> wrote:
>>
>> From: Hannes Reinecke <hare@xxxxxxx>
>>
>> The 'reserved' page array is used as a short-cut for mapping data,
>> saving us to allocate pages per request. However, the 'reserved' array
>> is only capable of holding one request, so this patch introduces a mutex
>> for protect 'sg_fd' against concurrent accesses.
>>
>> [toddpoynor@xxxxxxxxxx: backport to 3.18-4.9, fixup for bad ioctl
>> SG_SET_FORCE_LOW_DMA code removed in later versions and not modified by
>> the original patch.]
>>
>> commit 1bc0eb0446158cc76562176b80623aa119afee5b upstream.
>>
>> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
>> Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
>> Tested-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>> Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
>> Signed-off-by: Todd Poynor <toddpoynor@xxxxxxxxxx>
>> ---
>> Suggested for 4.9, 4.4, and 3.18. This version includes a trivial
>> fixup for some bad ioctl code that has been removed. The fix is
>> already in 4.12.
>>
>> Fixes a KASAN use-after-free bug found during multithreaded fuzz testing
>> of SCSI char device syscalls, where ioctl SG_SET_RESERVED_SIZE frees a
>> pre-allocated "reserve buffer" in a race with an I/O request that uses
>> the buffer.
>>
>> BUG: KASAN: use-after-free in bio_copy_user_iov+xx block/bio.c:1205
>> Call Trace:
>> ...
>> [<ffffffff81e051cf>] bio_copy_user_iov+0xcdf/0xe50 block/bio.c:1205
>> [<ffffffff81e3665f>] __blk_rq_map_user_iov block/blk-map.c:56 [inline]
>> [<ffffffff81e3665f>] blk_rq_map_user_iov+0x22f/0x770 block/blk-map.c:133
>> [<ffffffff81e36ca9>] blk_rq_map_user+0x109/0x180 block/blk-map.c:163
>> [<ffffffff8278f982>] sg_start_req drivers/scsi/sg.c:1766 [inline]
>> [<ffffffff8278f982>] sg_common_write.isra.21+0xc12/0x17a0
>> drivers/scsi/sg.c:775
>> [<ffffffff82793d1b>] sg_write+0x68b/0xb10 drivers/scsi/sg.c:678
>>
>> drivers/scsi/sg.c | 47 ++++++++++++++++++++++++++---------------------
>> 1 file changed, 26 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
>> index f753df25ba34..cf7e5f096988 100644
>> --- a/drivers/scsi/sg.c
>> +++ b/drivers/scsi/sg.c
>> @@ -142,6 +142,7 @@ typedef struct sg_fd { /* holds the state
>> of a file descriptor */
>> struct sg_device *parentdp; /* owning device */
>> wait_queue_head_t read_wait; /* queue read until command done
>> */
>> rwlock_t rq_list_lock; /* protect access to list in req_arr */
>> + struct mutex f_mutex; /* protect against changes in this fd */
>> int timeout; /* defaults to SG_DEFAULT_TIMEOUT */
>> int timeout_user; /* defaults to SG_DEFAULT_TIMEOUT_USER */
>> Sg_scatter_hold reserve; /* buffer held for this file
>> descriptor */
>> @@ -155,6 +156,7 @@ typedef struct sg_fd { /* holds the state
>> of a file descriptor */
>> unsigned char next_cmd_len; /* 0: automatic, >0: use on next
>> write() */
>> char keep_orphan; /* 0 -> drop orphan (def), 1 -> keep for
>> read() */
>> char mmap_called; /* 0 -> mmap() never called on this fd */
>> + char res_in_use; /* 1 -> 'reserve' array in use */
>> struct kref f_ref;
>> struct execute_work ew;
>> } Sg_fd;
>> @@ -198,7 +200,6 @@ static void sg_remove_sfp(struct kref *);
>> static Sg_request *sg_get_rq_mark(Sg_fd * sfp, int pack_id);
>> static Sg_request *sg_add_request(Sg_fd * sfp);
>> static int sg_remove_request(Sg_fd * sfp, Sg_request * srp);
>> -static int sg_res_in_use(Sg_fd * sfp);
>> static Sg_device *sg_get_dev(int dev);
>> static void sg_device_destroy(struct kref *kref);
>>
>> @@ -614,6 +615,7 @@ sg_write(struct file *filp, const char __user *buf,
>> size_t count, loff_t * ppos)
>> }
>> buf += SZ_SG_HEADER;
>> __get_user(opcode, buf);
>> + mutex_lock(&sfp->f_mutex);
>> if (sfp->next_cmd_len > 0) {
>> cmd_size = sfp->next_cmd_len;
>> sfp->next_cmd_len = 0; /* reset so only this write()
>> effected */
>> @@ -622,6 +624,7 @@ sg_write(struct file *filp, const char __user *buf,
>> size_t count, loff_t * ppos)
>> if ((opcode >= 0xc0) && old_hdr.twelve_byte)
>> cmd_size = 12;
>> }
>> + mutex_unlock(&sfp->f_mutex);
>> SCSI_LOG_TIMEOUT(4, sg_printk(KERN_INFO, sdp,
>> "sg_write: scsi opcode=0x%02x, cmd_size=%d\n", (int)
>> opcode, cmd_size));
>> /* Determine buffer size. */
>> @@ -721,7 +724,7 @@ sg_new_write(Sg_fd *sfp, struct file *file, const char
>> __user *buf,
>> sg_remove_request(sfp, srp);
>> return -EINVAL; /* either MMAP_IO or DIRECT_IO
>> (not both) */
>> }
>> - if (sg_res_in_use(sfp)) {
>> + if (sfp->res_in_use) {
>> sg_remove_request(sfp, srp);
>> return -EBUSY; /* reserve buffer already being
>> used */
>> }
>> @@ -892,7 +895,7 @@ sg_ioctl(struct file *filp, unsigned int cmd_in,
>> unsigned long arg)
>> return result;
>> if (val) {
>> sfp->low_dma = 1;
>> - if ((0 == sfp->low_dma) && (0 ==
>> sg_res_in_use(sfp))) {
>> + if ((0 == sfp->low_dma) && !sfp->res_in_use) {
>> val = (int) sfp->reserve.bufflen;
>> sg_remove_scat(sfp, &sfp->reserve);
>> sg_build_reserve(sfp, val);
>> @@ -967,12 +970,18 @@ sg_ioctl(struct file *filp, unsigned int cmd_in,
>> unsigned long arg)
>> return -EINVAL;
>> val = min_t(int, val,
>>
>> max_sectors_bytes(sdp->device->request_queue));
>> + mutex_lock(&sfp->f_mutex);
>> if (val != sfp->reserve.bufflen) {
>> - if (sg_res_in_use(sfp) || sfp->mmap_called)
>> + if (sfp->mmap_called ||
>> + sfp->res_in_use) {
>> + mutex_unlock(&sfp->f_mutex);
>> return -EBUSY;
>> + }
>> +
>> sg_remove_scat(sfp, &sfp->reserve);
>> sg_build_reserve(sfp, val);
>> }
>> + mutex_unlock(&sfp->f_mutex);
>> return 0;
>> case SG_GET_RESERVED_SIZE:
>> val = min_t(int, sfp->reserve.bufflen,
>> @@ -1727,13 +1736,22 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
>> md = &map_data;
>>
>> if (md) {
>> - if (!sg_res_in_use(sfp) && dxfer_len <= rsv_schp->bufflen)
>> + mutex_lock(&sfp->f_mutex);
>> + if (dxfer_len <= rsv_schp->bufflen &&
>> + !sfp->res_in_use) {
>> + sfp->res_in_use = 1;
>> sg_link_reserve(sfp, srp, dxfer_len);
>> - else {
>> + } else if ((hp->flags & SG_FLAG_MMAP_IO) &&
>> sfp->res_in_use) {
>> + mutex_unlock(&sfp->f_mutex);
>> + return -EBUSY;
>> + } else {
>> res = sg_build_indirect(req_schp, sfp, dxfer_len);
>> - if (res)
>> + if (res) {
>> + mutex_unlock(&sfp->f_mutex);
>> return res;
>> + }
>> }
>> + mutex_unlock(&sfp->f_mutex);
>>
>> md->pages = req_schp->pages;
>> md->page_order = req_schp->page_order;
>> @@ -2135,6 +2153,7 @@ sg_add_sfp(Sg_device * sdp)
>> rwlock_init(&sfp->rq_list_lock);
>>
>> kref_init(&sfp->f_ref);
>> + mutex_init(&sfp->f_mutex);
>> sfp->timeout = SG_DEFAULT_TIMEOUT;
>> sfp->timeout_user = SG_DEFAULT_TIMEOUT_USER;
>> sfp->force_packid = SG_DEF_FORCE_PACK_ID;
>> @@ -2210,20 +2229,6 @@ sg_remove_sfp(struct kref *kref)
>> schedule_work(&sfp->ew.work);
>> }
>>
>> -static int
>> -sg_res_in_use(Sg_fd * sfp)
>> -{
>> - const Sg_request *srp;
>> - unsigned long iflags;
>> -
>> - read_lock_irqsave(&sfp->rq_list_lock, iflags);
>> - for (srp = sfp->headrp; srp; srp = srp->nextrp)
>> - if (srp->res_used)
>> - break;
>> - read_unlock_irqrestore(&sfp->rq_list_lock, iflags);
>> - return srp ? 1 : 0;
>> -}
>> -
>> #ifdef CONFIG_SCSI_PROC_FS
>> static int
>> sg_idr_max_id(int id, void *p, void *data)
>> --
>> 2.14.1.480.gb18f417b89-goog
>>
>