From: Al Viro Date: Thu, 9 Oct 2014 03:44:00 +0000 (-0400) Subject: fix misuses of f_count() in ppp and netlink X-Git-Tag: v3.2.65~114 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=a59a6d8aad7120f8cf6b2393d2a1463de0c1ba6c fix misuses of f_count() in ppp and netlink commit 24dff96a37a2ca319e75a74d3929b2de22447ca6 upstream. we used to check for "nobody else could start doing anything with that opened file" by checking that refcount was 2 or less - one for descriptor table and one we'd acquired in fget() on the way to wherever we are. That was race-prone (somebody else might have had a reference to descriptor table and do fget() just as we'd been checking) and it had become flat-out incorrect back when we switched to fget_light() on those codepaths - unlike fget(), it doesn't grab an extra reference unless the descriptor table is shared. The same change allowed a race-free check, though - we are safe exactly when refcount is less than 2. It was a long time ago; pre-2.6.12 for ioctl() (the codepath leading to ppp one) and 2.6.17 for sendmsg() (netlink one). OTOH, netlink hadn't grown that check until 3.9 and ppp used to live in drivers/net, not drivers/net/ppp until 3.1. The bug existed well before that, though, and the same fix used to apply in old location of file. Signed-off-by: Al Viro [bwh: Backported to 3.2: drop changes to netlink_mmap_sendmsg()] Signed-off-by: Ben Hutchings --- diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 3ed983ce71af..4782d79f21c0 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -588,7 +588,7 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) if (file == ppp->owner) ppp_shutdown_interface(ppp); } - if (atomic_long_read(&file->f_count) <= 2) { + if (atomic_long_read(&file->f_count) < 2) { ppp_release(NULL, file); err = 0; } else