[PATCH] fbsplash: Fix mmap size and offset calculations

[savoundg at gmail.com]

From: Georges Savoundararadj <savoundg at gmail.com>

Before the commit 82c2fad, we were mapping the frame buffer device with
the size: yres * line_length.
This leads to a segmentation fault if the computed offset (yoffset *
line_length + xoffset * bytes_per_pixel) is greater than the size.

This commit maps the frame buffer device with the right offset avoiding
the need to map to a larger size as done in commit 82c2fad (by using
yres_virtual (if non-zero) instead of yres).

Signed-off-by: Georges Savoundararadj <savoundg at gmail.com>
Cc: Denys Vlasenko <vda.linux at googlemail.com>
Cc: Timo Teräs <timo.teras at iki.fi>
Cc: Dan Fandrich <dan at coneharvesters.com>
---
 miscutils/fbsplash.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/miscutils/fbsplash.c b/miscutils/fbsplash.c
index 3ddf8a2..5e20cdb 100644
--- a/miscutils/fbsplash.c
+++ b/miscutils/fbsplash.c
@@ -151,13 +151,13 @@ static void fb_open(const char *strfb_device)
 
 	// map the device in memory
 	G.addr = mmap(NULL,
-			(G.scr_var.yres_virtual ?: G.scr_var.yres) * G.scr_fix.line_length,
-			PROT_WRITE, MAP_SHARED, fbfd, 0);
+			G.scr_var.yres * G.scr_fix.line_length,
+			PROT_WRITE, MAP_SHARED, fbfd,
+			// point to the start of the visible screen
+			G.scr_var.yoffset * G.scr_fix.line_length + G.scr_var.xoffset * G.bytes_per_pixel);
 	if (G.addr == MAP_FAILED)
 		bb_perror_msg_and_die("mmap");
 
-	// point to the start of the visible screen
-	G.addr += G.scr_var.yoffset * G.scr_fix.line_length + G.scr_var.xoffset * G.bytes_per_pixel;
 	close(fbfd);
 }
 
-- 
2.8.0