From: Michal Koutný <mkoutny@xxxxxxxx>
Subject: prctl_set_mm: refactor checks from validate_prctl_map
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.
[akpm@xxxxxxxxxxxxxxxxxxxx: coding style fixes]
Link: http://lkml.kernel.org/r/20190502125203.24014-2-mkoutny@xxxxxxxx
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
Reviewed-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Cc: Mateusz Guzik <mguzik@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/sys.c | 51 ++++++++++++++++++++++++-------------------------
1 file changed, 25 insertions(+), 26 deletions(-)
--- a/kernel/sys.c~prctl_set_mm-refactor-checks-from-validate_prctl_map
+++ a/kernel/sys.c
@@ -1882,13 +1882,14 @@ exit_err:
}
/*
+ * 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;
int error = -EINVAL, i;
static const unsigned char offsets[] = {
@@ -1949,24 +1950,6 @@ static int validate_prctl_map(struct prc
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 +1976,18 @@ static int prctl_set_mm_map(int opt, con
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, con
}
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 +2095,11 @@ static int prctl_set_mm(int opt, unsigne
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 +2141,6 @@ static int prctl_set_mm(int opt, unsigne
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 +2180,7 @@ static int prctl_set_mm(int opt, unsigne
goto out;
}
- error = validate_prctl_map(&prctl_map);
+ error = validate_prctl_map_addr(&prctl_map);
if (error)
goto out;
_
