From fcbf94b9dedd2ce08e798a99aafc94fec8668161 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sat, 28 Apr 2012 08:29:56 -0700
Subject: Revert "autofs: work around unhappy compat problem on x86-64"
This reverts commit a32744d4abae24572eff7269bc17895c41bd0085.
While that commit was technically the right thing to do, and made the
x86-64 compat mode work identically to native 32-bit mode (and thus
fixing the problem with a 32-bit systemd install on a 64-bit kernel), it
turns out that the automount binaries had workarounds for this compat
problem.
Now, the workarounds are disgusting: doing an "uname()" to find out the
architecture of the kernel, and then comparing it for the 64-bit cases
and fixing up the size of the read() in automount for those. And they
were confused: it's not actually a generic 64-bit issue at all, it's
very much tied to just x86-64, which has different alignment for an
'u64' in 64-bit mode than in 32-bit mode.
But the end result is that fixing the compat layer actually breaks the
case of a 32-bit automount on a x86-64 kernel.
There are various approaches to fix this (including just doing a
"strcmp()" on current->comm and comparing it to "automount"), but I
think that I will do the one that teaches pipes about a special "packet
mode", which will allow user space to not have to care too deeply about
the padding at the end of the autofs packet.
That change will make the compat workaround unnecessary, so let's revert
it first, and get automount working again in compat mode. The
packetized pipes will then fix autofs for systemd.
Reported-and-requested-by: Michael Tokarev <mjt@tls.msk.ru>
Cc: Ian Kent <raven@themaw.net>
Cc: stable@kernel.org # for 3.3
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/autofs4/dev-ioctl.c | 1 -
1 file changed, 1 deletion(-)
(limited to 'fs/autofs4/dev-ioctl.c')
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index 9dacb8586701..3dfd615afb6b 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -385,7 +385,6 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
sbi->pipefd = pipefd;
sbi->pipe = pipe;
sbi->catatonic = 0;
- sbi->compat_daemon = is_compat_task();
}
out:
mutex_unlock(&sbi->wq_mutex);
--
cgit v1.2.3
From 64f371bc3107e69efce563a3d0f0e6880de0d537 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 29 Apr 2012 13:30:08 -0700
Subject: autofs: make the autofsv5 packet file descriptor use a packetized
pipe
The autofs packet size has had a very unfortunate size problem on x86:
because the alignment of 'u64' differs in 32-bit and 64-bit modes, and
because the packet data was not 8-byte aligned, the size of the autofsv5
packet structure differed between 32-bit and 64-bit modes despite
looking otherwise identical (300 vs 304 bytes respectively).
We first fixed that up by making the 64-bit compat mode know about this
problem in commit a32744d4abae ("autofs: work around unhappy compat
problem on x86-64"), and that made a 32-bit 'systemd' work happily on a
64-bit kernel because everything then worked the same way as on a 32-bit
kernel.
But it turned out that 'automount' had actually known and worked around
this problem in user space, so fixing the kernel to do the proper 32-bit
compatibility handling actually *broke* 32-bit automount on a 64-bit
kernel, because it knew that the packet sizes were wrong and expected
those incorrect sizes.
As a result, we ended up reverting that compatibility mode fix, and
thus breaking systemd again, in commit fcbf94b9dedd.
With both automount and systemd doing a single read() system call, and
verifying that they get *exactly* the size they expect but using
different sizes, it seemed that fixing one of them inevitably seemed to
break the other. At one point, a patch I seriously considered applying
from Michael Tokarev did a "strcmp()" to see if it was automount that
was doing the operation. Ugly, ugly.
However, a prettier solution exists now thanks to the packetized pipe
mode. By marking the communication pipe as being packetized (by simply
setting the O_DIRECT flag), we can always just write the bigger packet
size, and if user-space does a smaller read, it will just get that
partial end result and the extra alignment padding will simply be thrown
away.
This makes both automount and systemd happy, since they now get the size
they asked for, and the kernel side of autofs simply no longer needs to
care - it could pad out the packet arbitrarily.
Of course, if there is some *other* user of autofs (please, please,
please tell me it ain't so - and we haven't heard of any) that tries to
read the packets with multiple writes, that other user will now be
broken - the whole point of the packetized mode is that one system call
gets exactly one packet, and you cannot read a packet in pieces.
Tested-by: Michael Tokarev <mjt@tls.msk.ru>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: David Miller <davem@davemloft.net>
Cc: Ian Kent <raven@themaw.net>
Cc: Thomas Meyer <thomas@m3y3r.de>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/autofs4/autofs_i.h | 11 +++++++++++
fs/autofs4/dev-ioctl.c | 2 +-
fs/autofs4/inode.c | 2 +-
3 files changed, 13 insertions(+), 2 deletions(-)
(limited to 'fs/autofs4/dev-ioctl.c')
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index d8d8e7ba6a1e..908e18455413 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -269,6 +269,17 @@ int autofs4_fill_super(struct super_block *, void *, int);
struct autofs_info *autofs4_new_ino(struct autofs_sb_info *);
void autofs4_clean_ino(struct autofs_info *);
+static inline int autofs_prepare_pipe(struct file *pipe)
+{
+ if (!pipe->f_op || !pipe->f_op->write)
+ return -EINVAL;
+ if (!S_ISFIFO(pipe->f_dentry->d_inode->i_mode))
+ return -EINVAL;
+ /* We want a packet pipe */
+ pipe->f_flags |= O_DIRECT;
+ return 0;
+}
+
/* Queue management functions */
int autofs4_wait(struct autofs_sb_info *,struct dentry *, enum autofs_notify);
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index 3dfd615afb6b..aa9103f8f01b 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -376,7 +376,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
err = -EBADF;
goto out;
}
- if (!pipe->f_op || !pipe->f_op->write) {
+ if (autofs_prepare_pipe(pipe) < 0) {
err = -EPIPE;
fput(pipe);
goto out;
diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
index 14c7bc02349e..6e488ebe7784 100644
--- a/fs/autofs4/inode.c
+++ b/fs/autofs4/inode.c
@@ -290,7 +290,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
printk("autofs: could not open pipe file descriptor\n");
goto fail_dput;
}
- if (!pipe->f_op || !pipe->f_op->write)
+ if (autofs_prepare_pipe(pipe) < 0)
goto fail_fput;
sbi->pipe = pipe;
sbi->pipefd = pipefd;
--
cgit v1.2.3