scsi: sg: protect against races between mmap() and SG_SET_RESERVED_SIZE

Take f_mutex around mmap() processing to protect against races with the
SG_SET_RESERVED_SIZE ioctl.  Ensure the reserve buffer length remains
consistent during the mapping operation, and set the "mmap called" flag
to prevent further changes to the reserved buffer size as an atomic
operation with the mapping.

[mkp: fixed whitespace]

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index bda438e1fb1dbdcdaa2735f68776f8fbe0ae81e8..f5705a95319f8451df6490908029ced153face6b 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1262,6 +1262,7 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
        unsigned long req_sz, len, sa;
        Sg_scatter_hold *rsv_schp;
        int k, length;
+       int ret = 0;
 
        if ((!filp) || (!vma) || (!(sfp = (Sg_fd *) filp->private_data)))
                return -ENXIO;
@@ -1272,8 +1273,11 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
        if (vma->vm_pgoff)
                return -EINVAL; /* want no offset */
        rsv_schp = &sfp->reserve;
-       if (req_sz > rsv_schp->bufflen)
-               return -ENOMEM; /* cannot map more than reserved buffer */
+       mutex_lock(&sfp->f_mutex);
+       if (req_sz > rsv_schp->bufflen) {
+               ret = -ENOMEM;  /* cannot map more than reserved buffer */
+               goto out;
+       }
 
        sa = vma->vm_start;
        length = 1 << (PAGE_SHIFT + rsv_schp->page_order);
@@ -1287,7 +1291,9 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
        vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
        vma->vm_private_data = sfp;
        vma->vm_ops = &sg_mmap_vm_ops;
-       return 0;
+out:
+       mutex_unlock(&sfp->f_mutex);
+       return ret;
 }
 
 static void