[PATCH 3.18 22/24] scsi: sg: protect accesses to reserved page array

Greg Kroah-Hartman
2017-08-31T15:53:01Z

From: Hannes Reinecke <hare@suse.de>

commit 1bc0eb0446158cc76562176b80623aa119afee5b upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[toddpoynor@google.com: 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.]

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>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/scsi/sg.c | 47 ++++++++++++++++++++++++++---------------------
1 file changed, 26 insertions(+), 21 deletions(-)

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -153,6 +153,7 @@ typedef struct sg_fd { /* holds the sta
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 */
@@ -166,6 +167,7 @@ typedef struct sg_fd { /* holds the sta
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;
@@ -209,7 +211,6 @@ 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);

@@ -625,6 +626,7 @@ sg_write(struct file *filp, const char _
}
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 */
@@ -633,6 +635,7 @@ sg_write(struct file *filp, const char _
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. */
@@ -732,7 +735,7 @@ sg_new_write(Sg_fd *sfp, struct file *fi
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 */
}
@@ -917,7 +920,7 @@ sg_ioctl(struct file *filp, unsigned int
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);
@@ -992,12 +995,18 @@ sg_ioctl(struct file *filp, unsigned int
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,
@@ -1778,13 +1787,22 @@ sg_start_req(Sg_request *srp, unsigned c
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;
@@ -2191,6 +2209,7 @@ 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;
@@ -2266,20 +2285,6 @@ 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)