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firmware: xilinx: fix debugfs write handler

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- Userspace wants to write a string with `len` bytes, not counting the
   terminating NULL, so we should allocate `len+1` bytes. It looks like the
   current code relied on having a nullbyte directly behind `kern_buff`,
   which happens to work reliably as long as `len` isn't one of the kmalloc
   size classes.
 - strncpy_from_user() is completely wrong here; userspace is giving us a
   (not necessarily null-terminated) buffer and its length.
   strncpy_from_user() is for cases in which we don't know the length.
 - Don't let broken userspace allocate arbitrarily big kmalloc allocations.

Just use memdup_user_nul(), which is designed precisely for things like
this.

Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Jolly Shah <jolly.shah@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
This commit is contained in:
Jann Horn 2019-02-18 22:43:09 +01:00 committed by Michal Simek
parent 9e98c678c2
commit b9472f7d82
1 changed files with 4 additions and 11 deletions
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15
drivers/firmware/xilinx/zynqmp-debug.c
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@ -163,21 +163,14 @@ static ssize_t zynqmp_pm_debugfs_api_write(struct file *file,
strcpy(debugfs_buf, "");
if (*off != 0 || len == 0)
if (*off != 0 || len <= 1 || len > PAGE_SIZE - 1)
return -EINVAL;
kern_buff = kzalloc(len, GFP_KERNEL);
if (!kern_buff)
return -ENOMEM;
kern_buff = memdup_user_nul(ptr, len);
if (IS_ERR(kern_buff))
return PTR_ERR(kern_buff);
tmp_buff = kern_buff;
ret = strncpy_from_user(kern_buff, ptr, len);
if (ret < 0) {
ret = -EFAULT;
goto err;
}
/* Read the API name from a user request */
pm_api_req = strsep(&kern_buff, " ");