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authorLinus Torvalds <torvalds@linux-foundation.org>2017-08-23 18:16:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-08-23 18:16:11 -0700
commit143c97cc652949893c8056c679012f0aeccb80e5 (patch)
tree987e3a7fd939ae8169f7ddfc4d0b145a666536fa /drivers/tty/pty.c
parent2acf097f16abba684012cca670a61d94178bd1ab (diff)
Revert "pty: fix the cached path of the pty slave file descriptor in the master"
This reverts commit c8c03f1858331e85d397bacccd34ef409aae993c. It turns out that while fixing the ptmx file descriptor to have the correct 'struct path' to the associated slave pty is a really good thing, it breaks some user space tools for a very annoying reason. The problem is that /dev/ptmx and its associated slave pty (/dev/pts/X) are on different mounts. That was what caused us to have the wrong path in the first place (we would mix up the vfsmount of the 'ptmx' node, with the dentry of the pty slave node), but it also means that now while we use the right vfsmount, having the pty master open also keeps the pts mount busy. And it turn sout that that makes 'pbuilder' very unhappy, as noted by Stefan Lippers-Hollmann: "This patch introduces a regression for me when using pbuilder 0.228.7[2] (a helper to build Debian packages in a chroot and to create and update its chroots) when trying to umount /dev/ptmx (inside the chroot) on Debian/ unstable (full log and pbuilder configuration file[3] attached). [...] Setting up build-essential (12.3) ... Processing triggers for libc-bin (2.24-15) ... I: unmounting dev/ptmx filesystem W: Could not unmount dev/ptmx: umount: /var/cache/pbuilder/build/1340/dev/ptmx: target is busy (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1).)" apparently pbuilder tries to unmount the /dev/pts filesystem while still holding at least one master node open, which is arguably not very nice, but we don't break user space even when fixing other bugs. So this commit has to be reverted. I'll try to figure out a way to avoid caching the path to the slave pty in the master pty. The only thing that actually wants that slave pty path is the "TIOCGPTPEER" ioctl, and I think we could just recreate the path at that time. Reported-by: Stefan Lippers-Hollmann <s.l-h@gmx.de> Cc: Eric W Biederman <ebiederm@xmission.com> Cc: Christian Brauner <christian.brauner@canonical.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/tty/pty.c')
-rw-r--r--drivers/tty/pty.c7
1 files changed, 2 insertions, 5 deletions
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 1fc80ea87c13..284749fb0f6b 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -793,7 +793,6 @@ static int ptmx_open(struct inode *inode, struct file *filp)
struct tty_struct *tty;
struct path *pts_path;
struct dentry *dentry;
- struct vfsmount *mnt;
int retval;
int index;
@@ -806,7 +805,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
if (retval)
return retval;
- fsi = devpts_acquire(filp, &mnt);
+ fsi = devpts_acquire(filp);
if (IS_ERR(fsi)) {
retval = PTR_ERR(fsi);
goto out_free_file;
@@ -850,7 +849,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
pts_path = kmalloc(sizeof(struct path), GFP_KERNEL);
if (!pts_path)
goto err_release;
- pts_path->mnt = mnt;
+ pts_path->mnt = filp->f_path.mnt;
pts_path->dentry = dentry;
path_get(pts_path);
tty->link->driver_data = pts_path;
@@ -867,7 +866,6 @@ err_path_put:
path_put(pts_path);
kfree(pts_path);
err_release:
- mntput(mnt);
tty_unlock(tty);
// This will also put-ref the fsi
tty_release(inode, filp);
@@ -876,7 +874,6 @@ out:
devpts_kill_index(fsi, index);
out_put_fsi:
devpts_release(fsi);
- mntput(mnt);
out_free_file:
tty_free_file(filp);
return retval;

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