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

commit 6a8dadcca81fceff9976e8828cceb072873b7bd5 upstream.

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

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 8a9e139e28531943e02a3e093503d8c70954d111..fc1d9d33873fdf0a63b3a5b325871c82d7abcb50 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1254,6 +1254,7 @@ 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;
@@ -1264,8 +1265,11 @@ 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);
@@ -1279,7 +1283,9 @@ 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