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video: fbdev: sm712fb: Fix crash in smtcfb_read()

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commit bd771cf5c4254511cc4abb88f3dab3bd58bdf8e8 upstream.

Zheyu Ma reported this crash in the sm712fb driver when reading
three bytes from the framebuffer:

 BUG: unable to handle page fault for address: ffffc90001ffffff
 RIP: 0010:smtcfb_read+0x230/0x3e0
 Call Trace:
  vfs_read+0x198/0xa00
  ? do_sys_openat2+0x27d/0x350
  ? __fget_light+0x54/0x340
  ksys_read+0xce/0x190
  do_syscall_64+0x43/0x90

Fix it by removing the open-coded endianess fixup-code and
by moving the pointer post decrement out the fb_readl() function.

Reported-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Tested-by: Zheyu Ma <zheyuma97@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Helge Deller
2022-02-27 08:43:56 +01:00
committed by Greg Kroah-Hartman
parent ba09b04173
commit 72af881092
1 changed files with 7 additions and 18 deletions
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25
drivers/video/fbdev/sm712fb.c
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@@ -1047,7 +1047,7 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
if (count + p > total_size) if (count + p > total_size)
count = total_size - p; count = total_size - p;
buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count, GFP_KERNEL); buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!buffer) if (!buffer)
return -ENOMEM; return -ENOMEM;
@@ -1059,24 +1059,13 @@ static ssize_t smtcfb_read(struct fb_info *info, char __user *buf,
while (count) { while (count) {
c = (count > PAGE_SIZE) ? PAGE_SIZE : count; c = (count > PAGE_SIZE) ? PAGE_SIZE : count;
dst = buffer; dst = buffer;
for (i = c >> 2; i--;) { for (i = (c + 3) >> 2; i--;) {
*dst = fb_readl(src++); u32 val;
*dst = big_swap(*dst);
dst++;
}
if (c & 3) {
u8 *dst8 = (u8 *)dst;
u8 __iomem *src8 = (u8 __iomem *)src;
for (i = c & 3; i--;) { val = fb_readl(src);
if (i & 1) { *dst = big_swap(val);
*dst8++ = fb_readb(++src8); src++;
} else { dst++;
*dst8++ = fb_readb(--src8);
src8 += 2;
}
}
src = (u32 __iomem *)src8;
} }
if (copy_to_user(buf, buffer, c)) { if (copy_to_user(buf, buffer, c)) {