]> www.infradead.org Git - users/jedix/linux-maple.git/commit
pty: make sure super_block is still valid in final /dev/tty close
authorHerton R. Krzesinski <herton@redhat.com>
Thu, 14 Jan 2016 19:56:58 +0000 (17:56 -0200)
committerChuck Anderson <chuck.anderson@oracle.com>
Thu, 26 May 2016 22:44:57 +0000 (15:44 -0700)
commit1bc8cbf43aacc6513ad5c0d0ebad9f156715a0d0
tree1de4a247f1224f9a6d6f63fac42ebac80388f7ec
parent87ec623ace85aec4babb2f42238a8795290e3d1b
pty: make sure super_block is still valid in final /dev/tty close

Orabug: 23330844

[ Upstream commit 1f55c718c290616889c04946864a13ef30f64929 ]

Considering current pty code and multiple devpts instances, it's possible
to umount a devpts file system while a program still has /dev/tty opened
pointing to a previosuly closed pty pair in that instance. In the case all
ptmx and pts/N files are closed, umount can be done. If the program closes
/dev/tty after umount is done, devpts_kill_index will use now an invalid
super_block, which was already destroyed in the umount operation after
running ->kill_sb. This is another "use after free" type of issue, but now
related to the allocated super_block instance.

To avoid the problem (warning at ida_remove and potential crashes) for
this specific case, I added two functions in devpts which grabs additional
references to the super_block, which pty code now uses so it makes sure
the super block structure is still valid until pty shutdown is done.
I also moved the additional inode references to the same functions, which
also covered similar case with inode being freed before /dev/tty final
close/shutdown.

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>
Cc: stable@vger.kernel.org # 2.6.29+
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 38bdf7e3fb81c3d9cbbacab6f96e9fd28ff6c704)

Signed-off-by: Dan Duval <dan.duval@oracle.com>
drivers/tty/pty.c
fs/devpts/inode.c
include/linux/devpts_fs.h