[PATCH v17 39/45] sg: add mmap_sz tracking

[Douglas Gilbert <dgilbert@interlog.com>]

Track mmap_sz from prior mmap(2) call, per sg file descriptor. Also
reset this value whenever munmap(2) is called. Fail SG_FLAG_MMAP_IO
uses if mmap(2) hasn't been called or the memory associated with it
is not large enough for the current request.

Remove SG_FFD_MMAP_CALLED bit as it can be deduced from
sfp->mmap_sz where a value of 0 implies no mmap() call active.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/sg.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index fad396a3c4e7..6d6c00b55d87 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -121,8 +121,7 @@ enum sg_rq_state {	/* N.B. sg_rq_state_arr assumes SG_RS_AWAIT_RCV==2 */
 #define SG_FFD_FORCE_PACKID	0	/* receive only given pack_id/tag */
 #define SG_FFD_CMD_Q		1	/* clear: only 1 active req per fd */
 #define SG_FFD_KEEP_ORPHAN	2	/* policy for this fd */
-#define SG_FFD_MMAP_CALLED	3	/* mmap(2) system call made on fd */
-#define SG_FFD_Q_AT_TAIL	5	/* set: queue reqs at tail of blk q */
+#define SG_FFD_Q_AT_TAIL	3	/* set: queue reqs at tail of blk q */
 
 /* Bit positions (flags) for sg_device::fdev_bm bitmask follow */
 #define SG_FDEV_EXCLUDE		0	/* have fd open with O_EXCL */
@@ -231,6 +230,7 @@ struct sg_fd {		/* holds the state of a file descriptor */
 	atomic_t waiting;	/* number of requests awaiting receive */
 	atomic_t req_cnt;	/* number of requests */
 	int sgat_elem_sz;	/* initialized to scatter_elem_sz */
+	int mmap_sz;		/* byte size of previous mmap() call */
 	unsigned long ffd_bm[1];	/* see SG_FFD_* defines above */
 	pid_t tid;		/* thread id when opened */
 	u8 next_cmd_len;	/* 0: automatic, >0: use on next write() */
@@ -724,10 +724,14 @@ sg_write(struct file *filp, const char __user *p, size_t count, loff_t *ppos)
 static inline int
 sg_chk_mmap(struct sg_fd *sfp, int rq_flags, int len)
 {
+	if (unlikely(sfp->mmap_sz == 0))
+		return -EBADFD;
 	if (atomic_read(&sfp->submitted) > 0)
 		return -EBUSY;  /* already active requests on fd */
 	if (len > sfp->rsv_srp->sgat_h.buflen)
 		return -ENOMEM; /* MMAP_IO size must fit in reserve */
+	if (unlikely(len > sfp->mmap_sz))
+		return -ENOMEM; /* MMAP_IO size can't exceed mmap() size */
 	if (rq_flags & SG_FLAG_DIRECT_IO)
 		return -EINVAL; /* not both MMAP_IO and DIRECT_IO */
 	return 0;
@@ -1789,8 +1793,7 @@ sg_set_reserved_sz(struct sg_fd *sfp, int want_rsv_sz)
 		res = -EPROTO;
 		goto fini;
 	}
-	if (SG_RS_ACTIVE(o_srp) ||
-	    test_bit(SG_FFD_MMAP_CALLED, sfp->ffd_bm)) {
+	if (SG_RS_ACTIVE(o_srp) || sfp->mmap_sz > 0) {
 		res = -EBUSY;
 		goto fini;
 	}
@@ -2251,6 +2254,7 @@ sg_vma_close(struct vm_area_struct *vma)
 		pr_warn("%s: sfp null\n", __func__);
 		return;
 	}
+	sfp->mmap_sz = 0;
 	kref_put(&sfp->f_ref, sg_remove_sfp); /* get in: sg_vma_open() */
 }
 
@@ -2341,7 +2345,7 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
 	req_sz = vma->vm_end - vma->vm_start;
 	SG_LOG(3, sfp, "%s: vm_start=%pK, len=%d\n", __func__,
 	       (void *)vma->vm_start, (int)req_sz);
-	if (vma->vm_pgoff) {
+	if (unlikely(vma->vm_pgoff || req_sz < SG_DEF_SECTOR_SZ)) {
 		res = -EINVAL; /* only an offset of 0 accepted */
 		goto fini;
 	}
@@ -2355,7 +2359,7 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
 		res = -ENOMEM;
 		goto fini;
 	}
-	if (test_and_set_bit(SG_FFD_MMAP_CALLED, sfp->ffd_bm)) {
+	if (sfp->mmap_sz > 0) {
 		SG_LOG(1, sfp, "%s: multiple invocations on this fd\n",
 		       __func__);
 		res = -EADDRINUSE;
@@ -2372,6 +2376,7 @@ sg_mmap(struct file *filp, struct vm_area_struct *vma)
 			goto fini;
 		}
 	}
+	sfp->mmap_sz = req_sz;
 	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_private_data = sfp;
 	vma->vm_ops = &sg_mmap_vm_ops;
@@ -4022,8 +4027,7 @@ sg_proc_debug_fd(struct sg_fd *fp, char *obp, int len, unsigned long idx)
 		       (int)test_bit(SG_FFD_FORCE_PACKID, fp->ffd_bm),
 		       (int)test_bit(SG_FFD_KEEP_ORPHAN, fp->ffd_bm),
 		       fp->ffd_bm[0]);
-	n += scnprintf(obp + n, len - n, "   mmap_called=%d\n",
-		       test_bit(SG_FFD_MMAP_CALLED, fp->ffd_bm));
+	n += scnprintf(obp + n, len - n, "   mmap_sz=%d\n", fp->mmap_sz);
 	n += scnprintf(obp + n, len - n,
 		       "   submitted=%d waiting=%d   open thr_id=%d\n",
 		       atomic_read(&fp->submitted),
-- 
2.25.1