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proc: revalidate kernel thread inodes to root:root 

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>
This commit is contained in:
Alexey Dobriyan 2018-04-20 14:56:03 -07:00 committed by Linus Torvalds
parent 1e6306652b
commit 2e0ad552f5
1 changed files with 6 additions and 0 deletions
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6
fs/proc/base.c
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@ -1693,6 +1693,12 @@ void task_dump_owner(struct task_struct *task, umode_t mode,
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);