firmware: Fix an oops on reading fw_priv->fw in sysfs loading file
authorNeil Horman <nhorman@tuxdriver.com>
Mon, 2 Jan 2012 20:31:23 +0000 (15:31 -0500)
committerGreg Kroah-Hartman <gregkh@suse.de>
Thu, 12 Jan 2012 19:33:08 +0000 (11:33 -0800)
commitb8f5d3ec5824990acc0b1620fb211ee8e172cb64
tree2c781e8a56e134fe1e166f3a870774a19413b44b
parent75ba9e7ff5c9b6cf775f6968e4b362e38c8e325a
firmware: Fix an oops on reading fw_priv->fw in sysfs loading file

commit eea915bb0d1358755f151eaefb8208a2d5f3e10c upstream.

This oops was reported recently:
firmware_loading_store+0xf9/0x17b
dev_attr_store+0x20/0x22
sysfs_write_file+0x101/0x134
vfs_write+0xac/0xf3
sys_write+0x4a/0x6e
system_call_fastpath+0x16/0x1b

The complete backtrace was unfortunately not captured, but details can be found
here:
https://bugzilla.redhat.com/show_bug.cgi?id=769920

The cause is fairly clear.

Its caused by the fact that firmware_loading_store has a case 0 in its
switch statement that reads and writes the fw_priv->fw poniter without the
protection of the fw_lock mutex.  since there is a window between the time that
_request_firmware sets fw_priv->fw to NULL and the time the corresponding sysfs
file is unregistered, its possible for a user space application to race in, and
write a zero to the loading file, causing a NULL dereference in
firmware_loading_store.  Fix it by extending the protection of the fw_lock mutex
to cover all of the firware_loading_store function.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
drivers/base/firmware_class.c