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scsi: sg: protect accesses to 'reserved' page array
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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.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Tested-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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@hreinecke @martinkpetersen
hreinecke authored and martinkpetersen committed Apr 12, 2017
1 parent 136e57b commit 1bc0eb0
Showing 1 changed file with 25 additions and 20 deletions.
45 changes: 25 additions & 20 deletions drivers/scsi/sg.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand All @@ -153,6 +154,7 @@ 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;
Expand Down Expand Up @@ -196,7 +198,6 @@ 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);

Expand Down Expand Up @@ -612,6 +613,7 @@ 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 */
Expand All @@ -620,6 +622,7 @@ 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. */
Expand Down Expand Up @@ -719,7 +722,7 @@ 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 */
}
Expand Down Expand Up @@ -953,12 +956,18 @@ 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,
Expand Down Expand Up @@ -1718,13 +1727,22 @@ 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;
Expand Down Expand Up @@ -2125,6 +2143,7 @@ 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;
Expand Down Expand Up @@ -2198,20 +2217,6 @@ 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)
Expand Down

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