Patch "fs/fcntl: f_setown, avoid undefined behaviour" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

fs/fcntl: f_setown, avoid undefined behaviour

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-fcntl-f_setown-avoid-undefined-behaviour.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Slaby <[email protected]>
Date: Tue, 13 Jun 2017 13:35:51 +0200
Subject: fs/fcntl: f_setown, avoid undefined behaviour

From: Jiri Slaby <[email protected]>

commit fc3dc67471461c0efcb1ed22fb7595121d65fad9 upstream.

fcntl(0, F_SETOWN, 0x80000000) triggers:

UBSAN: Undefined behaviour in fs/fcntl.c:118:7
negation of -2147483648 cannot be represented in type 'int':
CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1
...
Call Trace:

...
[<ffffffffad8f0868>] ? f_setown+0x1d8/0x200 [<ffffffffad8f19a9>] ? SyS_fcntl+0x999/0xf30 [<ffffffffaed1fb00>] ? entry_SYSCALL_64_fastpath+0x23/0xc1

Fix that by checking the arg parameter properly (against INT_MAX) before "who = -who". And return immediatelly with -EINVAL in case it is wrong. Note that according to POSIX we can return EINVAL:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html

[EINVAL]
The cmd argument is F_SETOWN and the value of the argument is not valid as a process or process group identifier.

[v2] returns an error, v1 used to fail silently [v3] implement proper check for the bad value INT_MIN

---
 fs/fcntl.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -114,6 +114,10 @@ void f_setown(struct file *filp, unsigne
 	int who = arg;
 	type = PIDTYPE_PID;
 	if (who < 0) {
+		/* avoid overflow below */
+		if (who == INT_MIN)
+			return -EINVAL;
+
 		type = PIDTYPE_PGID;
 		who = -who;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/ipc-msg-make-msgrcv-work-with-long_min.patch queue-4.9/fs-fcntl-f_setown-avoid-undefined-behaviour.patch queue-4.9/acpi-scan-prefer-devices-without-_hid-_cid-for-_adr-matching.patch