[PATCH] media: bttv: Fix a NULL pointer dereference in setup_window_lock()

[Zhou Qingyang <zhou1615@umn.edu>]

In setup_window_lock(), the return value of videobuf_sg_alloc() is
assigned to variable new and there is a dereference of it after
that. the return value of videobuf_sg_alloc() could be NULL on
failure of allocation, which could lead to a NULL pointer dereference.

Fix this bug by adding a NULL check of new.

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: e5bd0260e7d3 ("V4L/DVB (5077): Bttv cropping support")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
---
The analysis employs differential checking to identify inconsistent 
security operations (e.g., checks or kfrees) between two code paths 
and confirms that the inconsistent operations are not recovered in the
current function or the callers, so they constitute bugs. 

Note that, as a bug found by static analysis, it can be a false
positive or hard to trigger. Multiple researchers have cross-reviewed
the bug.

 drivers/media/pci/bt8xx/bttv-driver.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c
index 8cc9bec43688..6338f98d845d 100644
--- a/drivers/media/pci/bt8xx/bttv-driver.c
+++ b/drivers/media/pci/bt8xx/bttv-driver.c
@@ -2182,6 +2182,8 @@ static int setup_window_lock(struct bttv_fh *fh, struct bttv *btv,
 		struct bttv_buffer *new;
 
 		new = videobuf_sg_alloc(sizeof(*new));
+		if (!new)
+			return -ENOMEM;
 		new->crop = btv->crop[!!fh->do_crop].rect;
 		bttv_overlay_risc(btv, &fh->ov, fh->ovfmt, new);
 		retval = bttv_switch_overlay(btv,fh,new);
-- 
2.25.1