Messages in this thread | | | Date | Thu, 7 May 2015 17:37:48 -0700 | From | josh@joshtrip ... | Subject | Re: [PATCH] devpts: If initialization failed, don't crash when opening /dev/ptmx |
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On Thu, May 07, 2015 at 03:59:19PM -0700, Andrew Morton wrote: > On Wed, 6 May 2015 17:35:47 -0700 Josh Triplett <josh@joshtriplett.org> wrote: > > > If devpts failed to initialize, it would store an ERR_PTR in the global > > devpts_mnt. A subsequent open of /dev/ptmx would call devpts_new_index, > > which would dereference devpts_mnt and crash. > > > > Avoid storing invalid values in devpts_mnt; leave it NULL instead. > > Make both devpts_new_index and devpts_pty_new fail gracefully with > > ENODEV in that case, which then becomes the return value to the > > userspace open call on /dev/ptmx. > > It looks like the system is pretty crippled if init_devptr_fs() fails. > Can the user actually get access to consoles and do useful things in > this situation? Maybe it would be better to just give up and panic?
Mounting devpts doesn't work without it, but you don't *need* to do that to run a viable system. A full-featured terminal might be unhappy. init=/bin/sh works, and a console login doesn't strictly require /dev/pts. A substantial initramfs or rescue system should work without /dev/pts mounted.
I think this falls under Linus's comments elsewhere about BUG versus WARN. The system can continue and will function to some degree. panic() is more suitable for "if I even return from this function, horrible things will start happening". With this patch, all the functions provided by devpts gracefully fail if devpts did, so I don't see a good reason to panic().
> > @@ -676,12 +689,15 @@ static int __init init_devpts_fs(void) > > struct ctl_table_header *table; > > > > if (!err) { > > + static struct vfsmount *mnt; > > static is weird. I assume this was a braino?
Copy/paste issue, yes. Fixed in v2.
- Josh Triplett
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