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    SubjectRe: [PATCH v2 1/1]: fs: pipe.c null pointer dereference + sign off
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    On Mon, 2009-10-19 at 11:13 -0700, Earl Chew wrote:
    > [ Exactly as before, but with sign off ]
    >

    You've got a few more submission related issues, see below.

    > This patch fixes a null pointer exception in pipe_rdwr_open() which
    > generates the stack trace:
    >
    >
    > > Unable to handle kernel NULL pointer dereference at 0000000000000028 RIP:
    > > [<ffffffff802899a5>] pipe_rdwr_open+0x35/0x70
    > > [<ffffffff8028125c>] __dentry_open+0x13c/0x230
    > > [<ffffffff8028143d>] do_filp_open+0x2d/0x40
    > > [<ffffffff802814aa>] do_sys_open+0x5a/0x100
    > > [<ffffffff8021faf3>] sysenter_do_call+0x1b/0x67
    >
    > This defect is also described in:
    > http://lkml.org/lkml/2009/10/14/184
    > http://bugzilla.kernel.org/show_bug.cgi?id=14416
    >
    >
    > The failure mode is triggered by an attempt to open an anonymous
    > pipe via /proc/pid/fd/* as exemplified by this script:
    >
    > =============================================================
    > #!/bin/sh
    > while : ; do
    > { echo y ; sleep 1 ; } | { while read ; do echo z$REPLY; done ; } &
    > PID=$!
    > OUT=$(ps -efl | grep 'sleep 1' | grep -v grep |
    > { read PID REST ; echo $PID; } )
    > OUT="${OUT%% *}"
    > DELAY=$((RANDOM * 1000 / 32768))
    > usleep $((DELAY * 1000 + RANDOM % 1000 ))
    > echo n > /proc/$OUT/fd/1 # Trigger defect
    > done
    > =============================================================
    >
    > Note that the failure window is quite small and I could only
    > reliably reproduce the defect by inserting a small delay
    > in pipe_rdwr_open(). For example:
    >
    > static int
    > pipe_rdwr_open(struct inode *inode, struct file *filp)
    > {
    > msleep(100);
    > mutex_lock(&inode->i_mutex);
    >
    >
    > Although the defect was observed in pipe_rdwr_open(), I think it
    > makes sense to replicate the change through all the pipe_*_open()
    > functions.
    >
    > The core of the change is to verify that inode->i_pipe has not
    > been released before attempting to manipulate it. If inode->i_pipe
    > is no longer present, return ENOENT to indicate so.
    >
    > The comment about potentially using atomic_t for i_pipe->readers
    > and i_pipe->writers has also been removed because it is no longer
    > relevant in this context. The inode->i_mutex lock must be used so
    > that inode->i_pipe can be dealt with correctly.
    >
    >
    > Signed-off-by: Earl Chew <earl_chew@agilent.com>
    >
    >
    > --- linux-2.6.21_mvlcge500/fs/pipe.c.orig 2009-10-15
    > 20:33:53.000000000 -0700
    > +++ linux-2.6.21_mvlcge500/fs/pipe.c 2009-10-15 21:21:25.000000000 -0700
    > @@ -712,36 +712,55 @@ pipe_rdwr_release(struct inode *inode, s
    > static int

    You patch looks like it might be line wrapped .. Sometimes mailers will
    do that if you don't tell them the content is already formatted.

    Also I see your using a MontaVista kernel, which is older than current
    mainline .. I would assume you tested this on a recent kernel also?

    > pipe_read_open(struct inode *inode, struct file *filp)
    > {
    > - /* We could have perhaps used atomic_t, but this and friends
    > - below are the only places. So it doesn't seem worthwhile. */
    > + int ret = -ENOENT;

    >From checkpatch,

    ERROR: code indent should use tabs where possible
    #125: FILE: fs/pipe.c:720:
    + ret = 0;$

    It looks like maybe your mailer (or copy and paste) may have stripped
    all the tabs off your patch. This makes is very difficult to apply.


    Daniel



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