[bug report] landlock: Add AUDIT_LANDLOCK_DOMAIN and log domain status

[Mickaël Salaün]

On Wed, Mar 12, 2025 at 11:33:29AM +0300, Dan Carpenter wrote:
> Hello Mickaël Salaün,
> 
> Commit 96cc6f48a8e4 ("landlock: Add AUDIT_LANDLOCK_DOMAIN and log
> domain status") from Mar 8, 2025 (linux-next), leads to the following
> Smatch static checker warning:
> 
> 	security/landlock/domain.c:66 get_current_exe()
> 	warn: 'size' unsigned <= 0

Hi,

Thanks for the report, I'll fix this issue.

I'm using Smatch's kchecker (commit f4f26f80d4f3) but I didn't get this
warning.  I tried with and without build_kernel_data.sh but I get the same
result. Which command are you using?

> 
> security/landlock/domain.c
>     39 static const void *get_current_exe(const char **const exe_str,
>     40                                    size_t *const exe_size)
>     41 {
>     42         const size_t buffer_size = LANDLOCK_PATH_MAX_SIZE;
>     43         struct mm_struct *mm = current->mm;
>     44         struct file *file __free(fput) = NULL;
>     45         char *buffer __free(kfree) = NULL;
>     46         const char *exe;
>     47         size_t size;
>     48 
>     49         if (!mm)
>     50                 return NULL;
>     51 
>     52         file = get_mm_exe_file(mm);
>     53         if (!file)
>     54                 return NULL;
>     55 
>     56         buffer = kmalloc(buffer_size, GFP_KERNEL);
>     57         if (!buffer)
>     58                 return ERR_PTR(-ENOMEM);
>     59 
>     60         exe = d_path(&file->f_path, buffer, buffer_size);
>     61         if (WARN_ON_ONCE(IS_ERR(exe)))
>     62                 /* Should never happen according to LANDLOCK_PATH_MAX_SIZE. */
>     63                 return ERR_CAST(exe);
>     64 
>     65         size = buffer + buffer_size - exe;
> 
> d_path() takes a buffer and returns exe which is a pointer to the
> somewhere in the middle of buffer.
> 
> --> 66         if (WARN_ON_ONCE(size <= 0))
> 
> So size can't be negative.  And also size is declared as unsigned so it
> can't be negative for that reason either.
> 
>     67                 return ERR_PTR(-ENAMETOOLONG);
>     68 
>     69         *exe_size = size;
>     70         *exe_str = exe;
>     71         return no_free_ptr(buffer);
>     72 }
> 
> regards,
> dan carpenter
>