2022-02-26 18:42:31

by Helge Deller

Subject: Re: [BUG] fbdev: sm712fb: Page fault in smtcfb_read

* Zheyu Ma <[email protected]>:
> I found a minor in the smtcfb_read() function of the driver sm712fb.
>
> This read function can not handle the case that the size of the
> buffer is 3 and does not check for it, which may cause a page fault.
>
> The following log reveals it:
>
> [ 2432.614490] BUG: unable to handle page fault for address: ffffc90001ffffff
> [ 2432.618474] RIP: 0010:smtcfb_read+0x230/0x3e0
> [ 2432.626551] Call Trace:
> [ 2432.626770] <TASK>
> [ 2432.626950] vfs_read+0x198/0xa00
> [ 2432.627225] ? do_sys_openat2+0x27d/0x350
> [ 2432.627552] ? __fget_light+0x54/0x340
> [ 2432.627871] ksys_read+0xce/0x190
> [ 2432.628143] do_syscall_64+0x43/0x90

Could you try the attached patch ?


diff --git a/drivers/video/fbdev/sm712fb.c b/drivers/video/fbdev/sm712fb.c
index 0dbc6bf8268a..ab45212ccf66 100644
--- a/drivers/video/fbdev/sm712fb.c
+++ b/drivers/video/fbdev/sm712fb.c
@@ -1047,7 +1047,7 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
if (count + p > total_size)
count = total_size - p;

- buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count, GFP_KERNEL);
+ buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!buffer)
return -ENOMEM;

@@ -1059,25 +1059,11 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
while (count) {
c = (count > PAGE_SIZE) ? PAGE_SIZE : count;
dst = buffer;
- for (i = c >> 2; i--;) {
- *dst = fb_readl(src++);
- *dst = big_swap(*dst);
+ for (i = (c + 3) >> 2; i--;) {
+ u32 val = fb_readl(src++);
+ *dst = big_swap(val);
dst++;
}
- if (c & 3) {
- u8 *dst8 = (u8 *)dst;
- u8 __iomem *src8 = (u8 __iomem *)src;
-
- for (i = c & 3; i--;) {
- if (i & 1) {
- *dst8++ = fb_readb(++src8);
- } else {
- *dst8++ = fb_readb(--src8);
- src8 += 2;
- }
- }
- src = (u32 __iomem *)src8;
- }

if (copy_to_user(buf, buffer, c)) {
err = -EFAULT;

2022-02-27 06:37:57

by Zheyu Ma

Subject: Re: [BUG] fbdev: sm712fb: Page fault in smtcfb_read

On Sat, Feb 26, 2022 at 11:03 PM Helge Deller <[email protected]> wrote:
>
> * Zheyu Ma <[email protected]>:
> > I found a minor in the smtcfb_read() function of the driver sm712fb.
> >
> > This read function can not handle the case that the size of the
> > buffer is 3 and does not check for it, which may cause a page fault.
> >
> > The following log reveals it:
> >
> > [ 2432.614490] BUG: unable to handle page fault for address: ffffc90001ffffff
> > [ 2432.618474] RIP: 0010:smtcfb_read+0x230/0x3e0
> > [ 2432.626551] Call Trace:
> > [ 2432.626770] <TASK>
> > [ 2432.626950] vfs_read+0x198/0xa00
> > [ 2432.627225] ? do_sys_openat2+0x27d/0x350
> > [ 2432.627552] ? __fget_light+0x54/0x340
> > [ 2432.627871] ksys_read+0xce/0x190
> > [ 2432.628143] do_syscall_64+0x43/0x90
>
> Could you try the attached patch ?

Good, the patch works for me, thanks.

Tested-by: Zheyu Ma <[email protected]>
>
>
> diff --git a/drivers/video/fbdev/sm712fb.c b/drivers/video/fbdev/sm712fb.c
> index 0dbc6bf8268a..ab45212ccf66 100644
> --- a/drivers/video/fbdev/sm712fb.c
> +++ b/drivers/video/fbdev/sm712fb.c
> @@ -1047,7 +1047,7 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
> if (count + p > total_size)
> count = total_size - p;
>
> - buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count, GFP_KERNEL);
> + buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
> if (!buffer)
> return -ENOMEM;
>
> @@ -1059,25 +1059,11 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
> while (count) {
> c = (count > PAGE_SIZE) ? PAGE_SIZE : count;
> dst = buffer;
> - for (i = c >> 2; i--;) {
> - *dst = fb_readl(src++);
> - *dst = big_swap(*dst);
> + for (i = (c + 3) >> 2; i--;) {
> + u32 val = fb_readl(src++);
> + *dst = big_swap(val);
> dst++;
> }
> - if (c & 3) {
> - u8 *dst8 = (u8 *)dst;
> - u8 __iomem *src8 = (u8 __iomem *)src;
> -
> - for (i = c & 3; i--;) {
> - if (i & 1) {
> - *dst8++ = fb_readb(++src8);
> - } else {
> - *dst8++ = fb_readb(--src8);
> - src8 += 2;
> - }
> - }
> - src = (u32 __iomem *)src8;
> - }
>
> if (copy_to_user(buf, buffer, c)) {
> err = -EFAULT;

Regards,
Zheyu Ma