Hi Greg,

below is the manual backport of an upstream patch to fix the build failure in kernel v4.14 in imsttfb.c.

It's not sufficient to just return from init_imstt() as the kernel then may crash later when it tries to access the non-existent framebuffer or cmap. Instead return failure to imsttfb_probe() so that the kernel will skip using that hardware/driver.

Can you please apply this patch to the v4.14 stable queue?

Thanks, Helge

----------- From: Zheng Wang zyytlz.wz@163.com

This is a manual backport of upstream patch c75f5a55061091030a13fef71b9995b89bc86213 to fix a build error in imsttfb.c in kernel v4.14.

A use-after-free bug may occur if init_imstt invokes framebuffer_release and free the info ptr. The caller, imsttfb_probe didn't notice that and still keep the ptr as private data in pdev.

If we remove the driver which will call imsttfb_remove to make cleanup, UAF happens.

Fix it by return error code if bad case happens in init_imstt.

Signed-off-by: Zheng Wang zyytlz.wz@163.com Signed-off-by: Helge Deller deller@gmx.de

diff --git a/drivers/video/fbdev/imsttfb.c b/drivers/video/fbdev/imsttfb.c index 6589d5f0a5a4..eaaa5f1c0f6f 100644 --- a/drivers/video/fbdev/imsttfb.c +++ b/drivers/video/fbdev/imsttfb.c @@ -1348,7 +1348,7 @@ static struct fb_ops imsttfb_ops = { .fb_ioctl = imsttfb_ioctl, };

-static void init_imstt(struct fb_info *info) +static int init_imstt(struct fb_info *info) { struct imstt_par *par = info->par; __u32 i, tmp, *ip, *end; @@ -1420,7 +1420,7 @@ static void init_imstt(struct fb_info *info) || !(compute_imstt_regvals(par, info->var.xres, info->var.yres))) { printk("imsttfb: %ux%ux%u not supported\n", info->var.xres, info->var.yres, info->var.bits_per_pixel); framebuffer_release(info); - return; + return -ENODEV; }

sprintf(info->fix.id, "IMS TT (%s)", par->ramdac == IBM ? "IBM" : "TVP"); @@ -1460,12 +1460,13 @@ static void init_imstt(struct fb_info *info) if (register_framebuffer(info) < 0) { fb_dealloc_cmap(&info->cmap); framebuffer_release(info); - return; + return -ENODEV; }

tmp = (read_reg_le32(par->dc_regs, SSTATUS) & 0x0f00) >> 8; fb_info(info, "%s frame buffer; %uMB vram; chip version %u\n", info->fix.id, info->fix.smem_len >> 20, tmp); + return 0; }

static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent) @@ -1474,6 +1475,7 @@ static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent) struct imstt_par *par; struct fb_info *info; struct device_node *dp; + int ret;

dp = pci_device_to_OF_node(pdev); if(dp) @@ -1525,10 +1527,10 @@ static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent) par->cmap_regs_phys = addr + 0x840000; par->cmap_regs = (__u8 *)ioremap(addr + 0x840000, 0x1000); info->pseudo_palette = par->palette; - init_imstt(info); - - pci_set_drvdata(pdev, info); - return 0; + ret = init_imstt(info); + if (!ret) + pci_set_drvdata(pdev, info); + return ret; }

static void imsttfb_remove(struct pci_dev *pdev)