Re: [PATCH v2] video: imsttfb: Fix use after free bug in imsttfb_probe due to lack of error-handling of init_imstt

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On 4/27/23 05:08, Zheng Wang wrote:
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.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>

applied.
Thanks!
Helge

---
v2:
- add return error code in another location.
---
  drivers/video/fbdev/imsttfb.c | 15 ++++++++-------
  1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/video/fbdev/imsttfb.c b/drivers/video/fbdev/imsttfb.c
index bea45647184e..975dd682fae4 100644
--- a/drivers/video/fbdev/imsttfb.c
+++ b/drivers/video/fbdev/imsttfb.c
@@ -1347,7 +1347,7 @@ static const 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");
@@ -1456,12 +1456,13 @@ static void init_imstt(struct fb_info *info)

  	if (register_framebuffer(info) < 0) {
  		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)
@@ -1529,10 +1530,10 @@ static int imsttfb_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
  	if (!par->cmap_regs)
  		goto error;
  	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;

  error:
  	if (par->dc_regs)





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