Re: [PATCH v3 4/4] mm: huge_memory: Use strscpy() instead of strcpy()

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+cc Kees Cook

Hi Barry,

On 31/10/24 09:01, Barry Song wrote:
On Thu, Oct 31, 2024 at 6:55 PM Maíra Canal <mcanal@xxxxxxxxxx> wrote:

Hi Barry,

On 30/10/24 20:07, Barry Song wrote:
On Thu, Oct 31, 2024 at 2:03 AM Maíra Canal <mcanal@xxxxxxxxxx> wrote:

Replace strcpy() with strscpy() in mm/huge_memory.c

strcpy() has been deprecated because it is generally unsafe, so help to
eliminate it from the kernel source.

Link: https://github.com/KSPP/linux/issues/88
Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
---
   mm/huge_memory.c | 4 ++--
   1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f92068864469..8f41a694433c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -989,7 +989,7 @@ static int __init setup_thp_anon(char *str)

          if (!str || strlen(str) + 1 > PAGE_SIZE)
                  goto err;
-       strcpy(str_dup, str);
+       strscpy(str_dup, str);

What is the difference between strcpy and strscpy without a size parameter?

we have already a check and goto err. strcpy() is entirely safe.
           if (!str || strlen(str) + 1 > PAGE_SIZE)
                   goto err;

My understanding is that we don't need this patch.

strcpy() is a deprecated interface [1]. From the GitHub issue I linked
in the commit description, Kees states: "A lot of kernel code is still
using strcpy(). While the CONFIG_FORTIFY_SOURCE wrapper macros tend to
make its use mostly safe, it would be nice to eliminate the function
from the kernel entirely."

I don't see any value added here since strscpy() has no size parameter and

As `str_dup` is a sized buffer, we don't need to specify the size
parameter.

we have checked strlen(str) + 1 > PAGE_SIZE to avoid parsing any pointless
bootcmd longer than PAGE_SIZE.

From my point of view, this is an extra layer of safety. A developer
could change `str_dup` to SZ_4K and leave PAGE_SIZE in the check. This
could pass by in a review and we would have a check that allows strings
bigger than the destination buffer in systems using 16KB pages.

But see that `split_huge_pages_write` uses `strcpy` without any checks.

I can remove the internal check from `setup_thp_anon` if you feel it
would be more suitable.

Best Regards,
- Maíra

> > But I have no objection to this patch if other people like it.


[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy

Best Regards,
- Maíra



          always = huge_anon_orders_always;
          madvise = huge_anon_orders_madvise;
@@ -4175,7 +4175,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,

                  tok = strsep(&buf, ",");
                  if (tok) {
-                       strcpy(file_path, tok);
+                       strscpy(file_path, tok);
                  } else {
                          ret = -EINVAL;
                          goto out;
--
2.46.2


Thanks
barry





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