Re: pipe_release oops.

[Dave Jones]

On Thu, Mar 07, 2013 at 04:21:13PM -0800, Linus Torvalds wrote:
 > On Thu, Mar 7, 2013 at 2:36 PM, Dave Jones <da...@redhat.com> wrote:
 > >
 > > The hits keep on coming..
 > >
 > > [  255.609172] BUG: unable to handle kernel NULL pointer dereference at 
 > > 0000000000000064
 > > [  255.610393] IP: [<ffffffff811bad62>] pipe_release+0x42/0xd0
 > 
 > Ok, I think this is the same issue as your fasync thing.
 > 
 > So add a "if (pipe) { }" in pipe_release() too.

Yeah, that does the trick.
I changed your other diff a little to use a goto, which reduces a level of 
indentation..

Signed-off-by: Dave Jones <da...@redhat.com>

diff --git a/fs/pipe.c b/fs/pipe.c
index 64a494c..49ba9cc 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -740,6 +740,9 @@ pipe_release(struct inode *inode, int decr, int decw)
 
        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
+       if (!pipe)
+               goto out_unlock;
+
        pipe->readers -= decr;
        pipe->writers -= decw;
 
@@ -750,6 +753,8 @@ pipe_release(struct inode *inode, int decr, int decw)
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
+
+out_unlock:
        mutex_unlock(&inode->i_mutex);
 
        return 0;
@@ -759,10 +764,11 @@ static int
 pipe_read_fasync(int fd, struct file *filp, int on)
 {
        struct inode *inode = file_inode(filp);
-       int retval;
+       int retval = 0;
 
        mutex_lock(&inode->i_mutex);
-       retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
+       if (inode->i_pipe)
+               retval = fasync_helper(fd, filp, on, 
&inode->i_pipe->fasync_readers);
        mutex_unlock(&inode->i_mutex);
 
        return retval;
@@ -773,10 +779,11 @@ static int
 pipe_write_fasync(int fd, struct file *filp, int on)
 {
        struct inode *inode = file_inode(filp);
-       int retval;
+       int retval = 0;
 
        mutex_lock(&inode->i_mutex);
-       retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
+       if (inode->i_pipe)
+               retval = fasync_helper(fd, filp, on, 
&inode->i_pipe->fasync_writers);
        mutex_unlock(&inode->i_mutex);
 
        return retval;
@@ -787,16 +794,22 @@ static int
 pipe_rdwr_fasync(int fd, struct file *filp, int on)
 {
        struct inode *inode = file_inode(filp);
-       struct pipe_inode_info *pipe = inode->i_pipe;
-       int retval;
+       struct pipe_inode_info *pipe;
+       int retval = 0;
 
        mutex_lock(&inode->i_mutex);
+       pipe = inode->i_pipe;
+       if (!pipe)
+               goto out_unlock;
+
        retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
        if (retval >= 0) {
                retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
                if (retval < 0) /* this can happen only if on == T */
                        fasync_helper(-1, filp, 0, &pipe->fasync_readers);
        }
+
+out_unlock:
        mutex_unlock(&inode->i_mutex);
        return retval;
 }
--
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