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authorHerton R. Krzesinski <herton@redhat.com>2016-01-14 17:56:58 -0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-02-06 23:45:46 -0800
commit1f55c718c290616889c04946864a13ef30f64929 (patch)
treed578b6dee5f2eb8ebe8f73ccba2b79a31252c52c
parent2831c89f42dcde440cfdccb9fee9f42d54bbc1ef (diff)
downloadlinux-1f55c718c290616889c04946864a13ef30f64929.tar.bz2
pty: make sure super_block is still valid in final /dev/tty close
Considering current pty code and multiple devpts instances, it's possible to umount a devpts file system while a program still has /dev/tty opened pointing to a previosuly closed pty pair in that instance. In the case all ptmx and pts/N files are closed, umount can be done. If the program closes /dev/tty after umount is done, devpts_kill_index will use now an invalid super_block, which was already destroyed in the umount operation after running ->kill_sb. This is another "use after free" type of issue, but now related to the allocated super_block instance. To avoid the problem (warning at ida_remove and potential crashes) for this specific case, I added two functions in devpts which grabs additional references to the super_block, which pty code now uses so it makes sure the super block structure is still valid until pty shutdown is done. I also moved the additional inode references to the same functions, which also covered similar case with inode being freed before /dev/tty final close/shutdown. Signed-off-by: Herton R. Krzesinski <herton@redhat.com> Cc: stable@vger.kernel.org # 2.6.29+ Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/pty.c9
-rw-r--r--fs/devpts/inode.c20
-rw-r--r--include/linux/devpts_fs.h4
3 files changed, 30 insertions, 3 deletions
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 3b5cde833ee5..2348fa613707 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -688,7 +688,7 @@ static void pty_unix98_shutdown(struct tty_struct *tty)
else
ptmx_inode = tty->link->driver_data;
devpts_kill_index(ptmx_inode, tty->index);
- iput(ptmx_inode); /* drop reference we acquired at ptmx_open */
+ devpts_del_ref(ptmx_inode);
}
static const struct tty_operations ptm_unix98_ops = {
@@ -785,9 +785,12 @@ static int ptmx_open(struct inode *inode, struct file *filp)
* still have /dev/tty opened pointing to the master/slave pair (ptmx
* is closed/released before /dev/tty), we must make sure that the inode
* is still valid when we call the final pty_unix98_shutdown, thus we
- * hold an additional reference to the ptmx inode
+ * hold an additional reference to the ptmx inode. For the same /dev/tty
+ * last close case, we also need to make sure the super_block isn't
+ * destroyed (devpts instance unmounted), before /dev/tty is closed and
+ * on its release devpts_kill_index is called.
*/
- ihold(inode);
+ devpts_add_ref(inode);
tty_add_file(tty, filp);
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 1f107fd51328..655f21f99160 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -575,6 +575,26 @@ void devpts_kill_index(struct inode *ptmx_inode, int idx)
mutex_unlock(&allocated_ptys_lock);
}
+/*
+ * pty code needs to hold extra references in case of last /dev/tty close
+ */
+
+void devpts_add_ref(struct inode *ptmx_inode)
+{
+ struct super_block *sb = pts_sb_from_inode(ptmx_inode);
+
+ atomic_inc(&sb->s_active);
+ ihold(ptmx_inode);
+}
+
+void devpts_del_ref(struct inode *ptmx_inode)
+{
+ struct super_block *sb = pts_sb_from_inode(ptmx_inode);
+
+ iput(ptmx_inode);
+ deactivate_super(sb);
+}
+
/**
* devpts_pty_new -- create a new inode in /dev/pts/
* @ptmx_inode: inode of the master
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 251a2090a554..e0ee0b3000b2 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -19,6 +19,8 @@
int devpts_new_index(struct inode *ptmx_inode);
void devpts_kill_index(struct inode *ptmx_inode, int idx);
+void devpts_add_ref(struct inode *ptmx_inode);
+void devpts_del_ref(struct inode *ptmx_inode);
/* mknod in devpts */
struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
void *priv);
@@ -32,6 +34,8 @@ void devpts_pty_kill(struct inode *inode);
/* Dummy stubs in the no-pty case */
static inline int devpts_new_index(struct inode *ptmx_inode) { return -EINVAL; }
static inline void devpts_kill_index(struct inode *ptmx_inode, int idx) { }
+static inline void devpts_add_ref(struct inode *ptmx_inode) { }
+static inline void devpts_del_ref(struct inode *ptmx_inode) { }
static inline struct inode *devpts_pty_new(struct inode *ptmx_inode,
dev_t device, int index, void *priv)
{