path: root/fs
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authorSukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>2009-11-17 18:35:43 -0800
committerGreg Kroah-Hartman <gregkh@suse.de>2009-12-11 15:18:05 -0800
commitedfacdd6f81119b9005615593f2cbd94b8c7e2d8 (patch)
tree9cdd79e4cc6f57b01848a20d5f79fcf46d6e9f16 /fs
parent68cb4f8e246bbbc649980be0628cae9265870a91 (diff)
devpts_get_tty() should validate inode
devpts_get_tty() assumes that the inode passed in is associated with a valid pty. But if the only reference to the pty is via a bind-mount, the inode passed to devpts_get_tty() while valid, would refer to a pty that no longer exists. With a lot of debug effort, Grzegorz Nosek developed a small program (see below) to reproduce a crash on recent kernels. This crash is a regression introduced by the commit: commit 527b3e4773628b30d03323a2cb5fb0d84441990f Author: Sukadev Bhattiprolu <sukadev@us.ibm.com> Date: Mon Oct 13 10:43:08 2008 +0100 To fix, ensure that the dentry associated with the inode has not yet been deleted/unhashed by devpts_pty_kill(). See also: https://lists.linux-foundation.org/pipermail/containers/2009-July/019273.html tty-bug.c: #define _GNU_SOURCE #include <fcntl.h> #include <sched.h> #include <stdlib.h> #include <sys/mount.h> #include <sys/signal.h> #include <unistd.h> #include <stdio.h> #include <linux/fs.h> void dummy(int sig) { } static int child(void *unused) { int fd; signal(SIGINT, dummy); signal(SIGHUP, dummy); pause(); /* cheesy synchronisation to wait for /dev/pts/0 to appear */ mount("/dev/pts/0", "/dev/console", NULL, MS_BIND, NULL); sleep(2); fd = open("/dev/console", O_RDWR); dup(0); dup(0); write(1, "Hello world!\n", sizeof("Hello world!\n")-1); return 0; } int main(void) { pid_t pid; char *stack; stack = malloc(16384); pid = clone(child, stack+16384, CLONE_NEWNS|SIGCHLD, NULL); open("/dev/ptmx", O_RDWR|O_NOCTTY|O_NONBLOCK); unlockpt(fd); grantpt(fd); sleep(2); kill(pid, SIGHUP); sleep(1); return 0; /* exit before child opens /dev/console */ } Reported-by: Grzegorz Nosek <root@localdomain.pl> Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> Tested-by: Serge Hallyn <serue@us.ibm.com> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'fs')
1 files changed, 14 insertions, 2 deletions
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index d5f8c96964b..8882ecc0f1b 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -517,11 +517,23 @@ int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
+ struct dentry *dentry;
+ struct tty_struct *tty;
BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
+ /* Ensure dentry has not been deleted by devpts_pty_kill() */
+ dentry = d_find_alias(pts_inode);
+ if (!dentry)
+ return NULL;
+ tty = NULL;
if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
- return (struct tty_struct *)pts_inode->i_private;
- return NULL;
+ tty = (struct tty_struct *)pts_inode->i_private;
+ dput(dentry);
+ return tty;
void devpts_pty_kill(struct tty_struct *tty)