- 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 <ja...@google.com>
---
WARNING: completely untested patch
drivers/firmware/xilinx/zynqmp-debug.c | 15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)
diff --git a/drivers/firmware/xilinx/zynqmp-debug.c
b/drivers/firmware/xilinx/zynqmp-debug.c
index 2771df6df379..90b66cdbfd58 100644
--- a/drivers/firmware/xilinx/zynqmp-debug.c
+++ b/drivers/firmware/xilinx/zynqmp-debug.c
@@ -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, " ");
--
2.21.0.rc0.258.g878e2cd30e-goog
