On 30.04.2019 11:18, Michal Koutný wrote:
> Despite comment of validate_prctl_map claims there are no capability
> checks, it is not completely true since commit 4d28df6152aa ("prctl:
> Allow local CAP_SYS_ADMIN changing exe_file"). Extract the check out of
> the function and make the function perform purely arithmetic checks.
>
> This patch should not change any behavior, it is mere refactoring for
> following patch.
>
> CC: Kirill Tkhai <ktk...@virtuozzo.com>
> CC: Cyrill Gorcunov <gorcu...@gmail.com>
> Signed-off-by: Michal Koutný <mkou...@suse.com>
Reviewed-by: Kirill Tkhai <ktk...@virtuozzo.com>
> ---
> kernel/sys.c | 45 ++++++++++++++++++++-------------------------
> 1 file changed, 20 insertions(+), 25 deletions(-)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 12df0e5434b8..e1acb444d7b0 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1882,10 +1882,12 @@ static int prctl_set_mm_exe_file(struct mm_struct
> *mm, unsigned int fd)
> }
>
> /*
> + * Check arithmetic relations of passed addresses.
> + *
> * WARNING: we don't require any capability here so be very careful
> * in what is allowed for modification from userspace.
> */
> -static int validate_prctl_map(struct prctl_mm_map *prctl_map)
> +static int validate_prctl_map_addr(struct prctl_mm_map *prctl_map)
> {
> unsigned long mmap_max_addr = TASK_SIZE;
> struct mm_struct *mm = current->mm;
> @@ -1949,24 +1951,6 @@ static int validate_prctl_map(struct prctl_mm_map
> *prctl_map)
> prctl_map->start_data))
> goto out;
>
> - /*
> - * Someone is trying to cheat the auxv vector.
> - */
> - if (prctl_map->auxv_size) {
> - if (!prctl_map->auxv || prctl_map->auxv_size >
> sizeof(mm->saved_auxv))
> - goto out;
> - }
> -
> - /*
> - * Finally, make sure the caller has the rights to
> - * change /proc/pid/exe link: only local sys admin should
> - * be allowed to.
> - */
> - if (prctl_map->exe_fd != (u32)-1) {
> - if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
> - goto out;
> - }
> -
> error = 0;
> out:
> return error;
> @@ -1993,11 +1977,17 @@ static int prctl_set_mm_map(int opt, const void
> __user *addr, unsigned long data
> if (copy_from_user(&prctl_map, addr, sizeof(prctl_map)))
> return -EFAULT;
>
> - error = validate_prctl_map(&prctl_map);
> + error = validate_prctl_map_addr(&prctl_map);
> if (error)
> return error;
>
> if (prctl_map.auxv_size) {
> + /*
> + * Someone is trying to cheat the auxv vector.
> + */
> + if (!prctl_map.auxv || prctl_map.auxv_size >
> sizeof(mm->saved_auxv))
> + return -EINVAL;
> +
> memset(user_auxv, 0, sizeof(user_auxv));
> if (copy_from_user(user_auxv,
> (const void __user *)prctl_map.auxv,
> @@ -2010,6 +2000,14 @@ static int prctl_set_mm_map(int opt, const void __user
> *addr, unsigned long data
> }
>
> if (prctl_map.exe_fd != (u32)-1) {
> + /*
> + * Make sure the caller has the rights to
> + * change /proc/pid/exe link: only local sys admin should
> + * be allowed to.
> + */
> + if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
> + return -EINVAL;
> +
> error = prctl_set_mm_exe_file(mm, prctl_map.exe_fd);
> if (error)
> return error;
> @@ -2097,7 +2095,7 @@ static int prctl_set_mm(int opt, unsigned long addr,
> unsigned long arg4, unsigned long arg5)
> {
> struct mm_struct *mm = current->mm;
> - struct prctl_mm_map prctl_map;
> + struct prctl_mm_map prctl_map = { .auxv = NULL, .auxv_size = 0, .exe_fd
> = -1 };
> struct vm_area_struct *vma;
> int error;
>
> @@ -2139,9 +2137,6 @@ static int prctl_set_mm(int opt, unsigned long addr,
> prctl_map.arg_end = mm->arg_end;
> prctl_map.env_start = mm->env_start;
> prctl_map.env_end = mm->env_end;
> - prctl_map.auxv = NULL;
> - prctl_map.auxv_size = 0;
> - prctl_map.exe_fd = -1;
>
> switch (opt) {
> case PR_SET_MM_START_CODE:
> @@ -2181,7 +2176,7 @@ static int prctl_set_mm(int opt, unsigned long addr,
> goto out;
> }
>
> - error = validate_prctl_map(&prctl_map);
> + error = validate_prctl_map_addr(&prctl_map);
> if (error)
> goto out;
>
>
