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

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>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 92cc658d8bc6d83f2118020e5b9417132f981a83..ddc18082cf6a2576cb42e93c68bd0eccabac9231 100644 (file)
--- 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 */
@@ -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;
@@ -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);
 
@@ -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 */
@@ -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.  */
@@ -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 */
                }
@@ -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,
@@ -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;
@@ -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;
@@ -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)