** Changed in: linux (Ubuntu)
Importance: Undecided => High
** Changed in: linux (Ubuntu)
Assignee: (unassigned) => Colin Ian King (colin-king)
** Changed in: linux (Ubuntu)
Status: Confirmed => In Progress
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https://bugs.launchpad.net/bugs/1876856
Title:
xenial: soft lockup in check_unsafe_exec()
Status in linux package in Ubuntu:
In Progress
Bug description:
Endless cycle was detected few times during ubuntu 16.04 testing insied
openvz VMs
dmesg output and crash dump ivestigation shows that foolowing ubuntu
16.04.patch is guilty
commit d6572202d986a84feda4cf7e6ce0bebaa18cb8fe
Author: Colin Ian King <[email protected]>
Date: Fri May 12 15:51:56 2017 +0100
UBUNTU:SAUCE: exec: ensure file system accounting in check_unsafe_exec is
correct
BugLink: http://bugs.launchpad.net/bugs/1672819
fs/exec.c:: check_unsafe_exec()
...
recheck:
fs_recheck = false;
t = p;
n_fs = 1;
spin_lock(&p->fs->lock);
rcu_read_lock();
while_each_thread(p, t) {
if (t->fs == p->fs)
n_fs++;
if (t->flags & (PF_EXITING | PF_FORKNOEXEC))
fs_recheck = true;
}
rcu_read_unlock();
if (p->fs->users > n_fs) {
if (fs_recheck) {
spin_unlock(&p->fs->lock);
goto recheck; <<<<<< cycles forever
}
bprm->unsafe |= LSM_UNSAFE_SHARE;
} else
p->fs->in_exec = 1;
spin_unlock(&p->fs->lock);
dmesg example is attached,
let me know if you want to look at crash dump image.
Bug is xenial-specific (4.4 kernel), other kernel branches seems are not
affected.
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