[PATCH] fbdev: fix potential buffer overflow in do_register_framebuffer()

The current implementation may lead to buffer overflow when:
1.  Unregistration creates NULL gaps in registered_fb[]
2.  All array slots become occupied despite num_registered_fb < FB_MAX
3.  The registration loop exceeds array bounds

Add boundary check to prevent registered_fb[FB_MAX] access.

Signed-off-by: Yongzhen Zhang <redacted>
---
 drivers/video/fbdev/core/fbmem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index dfcf5e4d1d4c..53f1719b1ae1 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c

@@ -449,6 +449,9 @@ static int do_register_framebuffer(struct fb_info *fb_info)
 		if (!registered_fb[i])
 			break;
 
+	if (i >= FB_MAX)
+		return -ENXIO;
+
 	if (!fb_info->modelist.prev || !fb_info->modelist.next)
 		INIT_LIST_HEAD(&fb_info->modelist);
 

-- 
2.25.1