pty: make sure super_block is still valid in final /dev/tty close
[ Upstream commit 1f55c718c2
]
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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
wifi-calibration
parent
614f8734d1
commit
38bdf7e3fb
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@ -679,7 +679,7 @@ static void pty_unix98_shutdown(struct tty_struct *tty)
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else
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ptmx_inode = tty->link->driver_data;
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devpts_kill_index(ptmx_inode, tty->index);
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iput(ptmx_inode); /* drop reference we acquired at ptmx_open */
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devpts_del_ref(ptmx_inode);
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}
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static const struct tty_operations ptm_unix98_ops = {
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@ -776,9 +776,12 @@ static int ptmx_open(struct inode *inode, struct file *filp)
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* still have /dev/tty opened pointing to the master/slave pair (ptmx
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* is closed/released before /dev/tty), we must make sure that the inode
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* is still valid when we call the final pty_unix98_shutdown, thus we
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* hold an additional reference to the ptmx inode
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* hold an additional reference to the ptmx inode. For the same /dev/tty
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* last close case, we also need to make sure the super_block isn't
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* destroyed (devpts instance unmounted), before /dev/tty is closed and
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* on its release devpts_kill_index is called.
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*/
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ihold(inode);
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devpts_add_ref(inode);
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tty_add_file(tty, filp);
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@ -569,6 +569,26 @@ void devpts_kill_index(struct inode *ptmx_inode, int idx)
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mutex_unlock(&allocated_ptys_lock);
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}
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/*
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* pty code needs to hold extra references in case of last /dev/tty close
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*/
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void devpts_add_ref(struct inode *ptmx_inode)
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{
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struct super_block *sb = pts_sb_from_inode(ptmx_inode);
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atomic_inc(&sb->s_active);
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ihold(ptmx_inode);
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}
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void devpts_del_ref(struct inode *ptmx_inode)
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{
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struct super_block *sb = pts_sb_from_inode(ptmx_inode);
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iput(ptmx_inode);
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deactivate_super(sb);
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}
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/**
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* devpts_pty_new -- create a new inode in /dev/pts/
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* @ptmx_inode: inode of the master
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@ -19,6 +19,8 @@
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int devpts_new_index(struct inode *ptmx_inode);
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void devpts_kill_index(struct inode *ptmx_inode, int idx);
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void devpts_add_ref(struct inode *ptmx_inode);
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void devpts_del_ref(struct inode *ptmx_inode);
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/* mknod in devpts */
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struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
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void *priv);
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@ -32,6 +34,8 @@ void devpts_pty_kill(struct inode *inode);
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/* Dummy stubs in the no-pty case */
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static inline int devpts_new_index(struct inode *ptmx_inode) { return -EINVAL; }
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static inline void devpts_kill_index(struct inode *ptmx_inode, int idx) { }
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static inline void devpts_add_ref(struct inode *ptmx_inode) { }
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static inline void devpts_del_ref(struct inode *ptmx_inode) { }
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static inline struct inode *devpts_pty_new(struct inode *ptmx_inode,
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dev_t device, int index, void *priv)
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{
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