[PATCH 4.14 046/189] proc: revalidate kernel thread inodes to root:root

Greg Kroah-Hartman
2018-06-18T08:31:08Z

From: Alexey Dobriyan <adobriyan@gmail.com>

[ Upstream commit 2e0ad552f5f8cd0fda02bc45fcd2b89821c62fd1 ]

task_dump_owner() has the following code:

mm = task->mm;
if (mm) {
if (get_dumpable(mm) != SUID_DUMP_USER) {
uid = ...
}
}

Check for ->mm is buggy -- kernel thread might be borrowing mm
and inode will go to some random uid:gid pair.

Link: http://lkml.kernel.org/r/20180412220109.GA20978@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/proc/base.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1694,6 +1694,12 @@ void task_dump_owner(struct task_struct
kuid_t uid;
kgid_t gid;

+ if (unlikely(task->flags & PF_KTHREAD)) {
+ *ruid = GLOBAL_ROOT_UID;
+ *rgid = GLOBAL_ROOT_GID;
+ return;
+ }
+
/* Default to the tasks effective ownership */
rcu_read_lock();
cred = __task_cred(task);