Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751289Ab2BVFny (ORCPT ); Wed, 22 Feb 2012 00:43:54 -0500 Received: from out5-smtp.messagingengine.com ([66.111.4.29]:33981 "EHLO out5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750769Ab2BVFnx (ORCPT ); Wed, 22 Feb 2012 00:43:53 -0500 X-Sasl-enc: +36+hUnrb0/3h/hqLv27a1thRimbnKH4qdBUBjmxjXZYNvNDbKtvoKJqHA 1329889431 Message-ID: <1329889428.2193.45.camel@perseus.themaw.net> Subject: Re: compat: autofs v5 packet size ambiguity - update From: Ian Kent To: Linus Torvalds Cc: David Miller , linux-kernel@vger.kernel.org, "H. Peter Anvin" , autofs@vger.kernel.org, Thomas Meyer , Al Viro Date: Wed, 22 Feb 2012 13:43:48 +0800 In-Reply-To: References: <20120221.221609.218135609185671883.davem@davemloft.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 (3.2.3-1.fc16) Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6803 Lines: 193 On Tue, 2012-02-21 at 20:56 -0800, Linus Torvalds wrote: > On Tue, Feb 21, 2012 at 7:47 PM, Linus Torvalds > wrote: > > > > And then it does a AUTOFS_IOC_PROTOVER ioctl to see what the protocol > > version is. > > > > So we could just decide that > > > > (a) we add a mount option for the packet size (or just "v6" - which > > would be "v5 with a fixed packet size") > > > > (b) in the absence of an explicit mount option, we look at > > is_compat_task() for the first AUTOFS_IOC_PROTOVER ioctl we get. > > Ok, so here's a patch that does that. Well, it doesn't do that (a) > part, but it does the auto-detection of whether the daemon is a compat > process or not. > > THIS IS UNTESTED. Thomas - could you test this in your environment? I > added your "Tested-by:", but that's really for the previous patch that > tested is_compat_task() in the wrong context. > > Linus How about .... ummm .. I haven't updated the patch description in case this is wrong, just put together what I think should work ... TOTALLY UNTESTED also. autofs: work around unhappy compat problem on x86-64 From: Ian Kent When the autofs protocol version 5 packet type was added in commit 5c0a32fc2cd0 ("autofs4: add new packet type for v5 communications"), it obvously tried quite hard to be word-size agnostic, and uses explicitly sized fields that are all correctly aligned. However, with the final "char name[NAME_MAX+1]" array at the end, the actual size of the structure ends up being not very well defined: because the struct isn't marked 'packed', doing a "sizeof()" on it will align the size of the struct up to the biggest alignment of the members it has. And despite all the members being the same, the alignment of them is different: a "__u64" has 4-byte alignment on x86-32, but native 8-byte alignment on x86-64. And while 'NAME_MAX+1' ends up being a nice round number (256), the name[] array starts out a 4-byte aligned. End result: the "packed" size of the structure is 300 bytes: 4-byte, but not 8-byte aligned. As a result, despite all the fields being in the same place on all architectures, sizeof() will round up that size to 304 bytes on architectures that have 8-byte alignment for u64. Note that this is *not* a problem for 32-bit compat mode on POWER, since there __u64 is 8-byte aligned even in 32-bit mode. But on x86, 32-bit and 64-bit alignment is different for 64-bit entities, and as a result the structure that has exactly the same layout has different sizes. So on x86-64, but no other architecture, we will just subtract 4 from the size of the structure when running in a compat task. That way we will write the properly sized packet that user mode expects. Not pretty. Sadly, this very subtle, and unnecessary, size difference has been encoded in user space that wants to read packets of *exactly* the right size, and will refuse to touch anything else. Reported-and-tested-by: Thomas Meyer Cc: Ian Kent --- fs/autofs4/autofs_i.h | 1 + fs/autofs4/dev-ioctl.c | 3 +++ fs/autofs4/inode.c | 1 + fs/autofs4/root.c | 8 ++++++++ fs/autofs4/waitq.c | 23 ++++++++++++++++++++--- 5 files changed, 33 insertions(+), 3 deletions(-) diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index d8d8e7b..eb1cc92 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -110,6 +110,7 @@ struct autofs_sb_info { int sub_version; int min_proto; int max_proto; + int compat_daemon; unsigned long exp_timeout; unsigned int type; int reghost_enabled; diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c index 76741d8..868fd57 100644 --- a/fs/autofs4/dev-ioctl.c +++ b/fs/autofs4/dev-ioctl.c @@ -265,6 +265,9 @@ static int autofs_dev_ioctl_open_mountpoint(const char *name, dev_t devid) } autofs_dev_ioctl_fd_install(fd, filp); + + if (sbi->compat_daemon < 0) + sbi->compat_daemon = is_compat_task(); } return fd; diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c index e16980b..2920bbd 100644 --- a/fs/autofs4/inode.c +++ b/fs/autofs4/inode.c @@ -224,6 +224,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent) set_autofs_type_indirect(&sbi->type); sbi->min_proto = 0; sbi->max_proto = 0; + sbi->compat_daemon = -1; /* unknown */ mutex_init(&sbi->wq_mutex); mutex_init(&sbi->pipe_mutex); spin_lock_init(&sbi->fs_lock); diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c index 75e5f1c..9c620bf 100644 --- a/fs/autofs4/root.c +++ b/fs/autofs4/root.c @@ -71,6 +71,14 @@ const struct dentry_operations autofs4_dentry_operations = { .d_release = autofs4_dentry_release, }; +static int autofs4_root_dir_open(struct inode *inode, struct file *file) +{ + struct autofs_sb_info *sbi= autofs4_sbi(file->f_path.dentry->d_sb); + if (sbi->compat_daemon < 0) + sbi->compat_daemon = is_compat_task(); + return dcache_dir_open(inode, file); +} + static void autofs4_add_active(struct dentry *dentry) { struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb); diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c index da8876d..8ec8507 100644 --- a/fs/autofs4/waitq.c +++ b/fs/autofs4/waitq.c @@ -15,6 +15,7 @@ #include #include #include +#include #include "autofs_i.h" /* We make this a static variable rather than a part of the superblock; it @@ -91,7 +92,24 @@ static int autofs4_write(struct autofs_sb_info *sbi, return (bytes > 0); } - + +/* + * The autofs_v5 packet was misdesigned. + * + * The packets are identical on x86-32 and x86-64, but have different + * alignment. Which means that 'sizeof()' will give different results. + * Fix it up for the case of running 32-bit user mode on a 64-bit kernel. + */ +static noinline size_t autofs_v5_packet_size(struct autofs_sb_info *sbi) +{ + size_t pktsz = sizeof(struct autofs_v5_packet); +#if defined(CONFIG_X86_64) && defined(CONFIG_COMPAT) + if (sbi->compat_daemon > 0) + pktsz -= 4; +#endif + return pktsz; +} + static void autofs4_notify_daemon(struct autofs_sb_info *sbi, struct autofs_wait_queue *wq, int type) @@ -155,8 +173,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi, { struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet; - pktsz = sizeof(*packet); - + pktsz = autofs_v5_packet_size(sbi); packet->wait_queue_token = wq->wait_queue_token; packet->len = wq->name.len; memcpy(packet->name, wq->name.name, wq->name.len); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/