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Subject[PATCH 2/3] prctl_set_mm: Refactor checks from validate_prctl_map
Date
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 <ktkhai@virtuozzo.com>
CC: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Michal Koutný <mkoutny@suse.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;

--
2.16.4
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