Date:	Sat, 13 Mar 2010 08:18:59 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	andi@...stfloor.org
Subject: Re: [PATCH 1/2] exec: Rediff wrecked bits of usermodehelper overhaul

On Sat, Mar 13, 2010 at 12:33:48PM +0100, Oleg Nesterov wrote:
> Neil, you confused the ordering ;)
> 
> This is "2/2", the second patch. And the next email is "1/2".
> 
Gahh!  You're right!  Dang it!  Sorry.  Andrew, want me to repost?  I can fix
the patch names while I'm at it :)
Neil

> 
> On 03/12, Neil Horman wrote:
> >
> > Rediff of the usermodehelper changes after all the wreckage.  This patch
> > encompasses the patches that were formally in -mm as:
> > 
> > kmod-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limit.patch
> > kmod-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limitcleanup.patch
> > 
> > kmod: replace call_usermodehelper_pipe() with use of umh init function and resolve limit
> > 
> > The first patch in this series introduced an init function to the
> > call_usermodehelper api so that processes could be customized by caller.
> > This patch takes advantage of that fact, by customizing the helper in
> > do_coredump to create the pipe and set its core limit to one (for our
> > recusrsion check).  This lets us clean up the previous uglyness in the
> > usermodehelper internals and factor call_usermodehelper out entirely.
> > While I'm at it, we can also modify the helper setup to look for a core
> > limit value of 1 rather than zero for our recursion check
> > 
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > CC: Oleg Nesterov <oleg@...hat.com>
> > CC: Andi Kleen <andi@...stfloor.org>
> > 
> > 
> >  fs/exec.c            |   63 ++++++++++++++++++++++++++++++++++-----
> >  include/linux/kmod.h |    7 ----
> >  kernel/kmod.c        |   82 ---------------------------------------------------
> >  3 files changed, 56 insertions(+), 96 deletions(-)
> > 
> > diff --git a/fs/exec.c b/fs/exec.c
> > index f351cdb..64a50b4 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1784,6 +1784,50 @@ static void wait_for_dump_helpers(struct file *file)
> >  }
> >  
> >  
> > +/*
> > + * uhm_pipe_setup
> > + * helper function to customize the process used
> > + * to collect the core in userspace.  Specifically
> > + * it sets up a pipe and installs it as fd 0 (stdin)
> > + * for the process.  Returns 0 on success, or
> > + * PTR_ERR on failure.
> > + * Note that it also sets the core limit to 1.  This
> > + * is a special value that we use to trap recursive
> > + * core dumps
> > + */
> > +static int umh_pipe_setup(struct subprocess_info *info)
> > +{
> > +	struct file *rp, *wp;
> > +	struct fdtable *fdt;
> > +	struct coredump_params *cp = (struct coredump_params *)info->data;
> > +	struct files_struct *cf = current->files;
> > +
> > +	wp = create_write_pipe(0);
> > +	if (IS_ERR(wp))
> > +		return PTR_ERR(wp);
> > +
> > +	rp = create_read_pipe(wp, 0);
> > +	if (IS_ERR(rp)) {
> > +		free_write_pipe(wp);
> > +		return PTR_ERR(rp);
> > +	}
> > +
> > +	cp->file = wp;
> > +
> > +	sys_close(0);
> > +	fd_install(0, rp);
> > +	spin_lock(&cf->file_lock);
> > +	fdt = files_fdtable(cf);
> > +	FD_SET(0, fdt->open_fds);
> > +	FD_CLR(0, fdt->close_on_exec);
> > +	spin_unlock(&cf->file_lock);
> > +
> > +	/* and disallow core files too */
> > +	current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
> > +
> > +	return 0;
> > +}
> > +
> >  void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >  {
> >  	struct core_state core_state;
> > @@ -1871,15 +1915,15 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >  		goto fail_unlock;
> >  
> >   	if (ispipe) {
> > -		if (cprm.limit == 0) {
> > +		if (cprm.limit == 1) {
> >  			/*
> >  			 * Normally core limits are irrelevant to pipes, since
> >  			 * we're not writing to the file system, but we use
> > -			 * cprm.limit of 0 here as a speacial value. Any
> > -			 * non-zero limit gets set to RLIM_INFINITY below, but
> > +			 * cprm.limit of 1 here as a speacial value. Any
> > +			 * non-1 limit gets set to RLIM_INFINITY below, but
> >  			 * a limit of 0 skips the dump.  This is a consistent
> >  			 * way to catch recursive crashes.  We can still crash
> > -			 * if the core_pattern binary sets RLIM_CORE =  !0
> > +			 * if the core_pattern binary sets RLIM_CORE =  !1
> >  			 * but it runs as root, and can do lots of stupid things
> >  			 * Note that we use task_tgid_vnr here to grab the pid
> >  			 * of the process group leader.  That way we get the
> > @@ -1887,7 +1931,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >  			 * core_pattern process dies.
> >  			 */
> >  			printk(KERN_WARNING
> > -				"Process %d(%s) has RLIMIT_CORE set to 0\n",
> > +				"Process %d(%s) has RLIMIT_CORE set to 1\n",
> >  				task_tgid_vnr(current), current->comm);
> >  			printk(KERN_WARNING "Aborting core\n");
> >  			goto fail_unlock;
> > @@ -1911,8 +1955,13 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> >  		cprm.limit = RLIM_INFINITY;
> >  
> >  		/* SIGPIPE can happen, but it's just never processed */
> > -		if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL,
> > -				&cprm.file)) {
> > +		cprm.file = NULL;
> > +		if (call_usermodehelper_fns(helper_argv[0], helper_argv, NULL,
> > +					    UMH_WAIT_EXEC, umh_pipe_setup,
> > +					    NULL, &cprm)) {
> > +			if (cprm.file)
> > +				filp_close(cprm.file, NULL);
> > +
> >   			printk(KERN_INFO "Core dump to %s pipe failed\n",
> >  			       corename);
> >  			goto fail_dropcount;
> > diff --git a/include/linux/kmod.h b/include/linux/kmod.h
> > index f9edf63..5c05877 100644
> > --- a/include/linux/kmod.h
> > +++ b/include/linux/kmod.h
> > @@ -62,7 +62,6 @@ struct subprocess_info {
> >  	char **envp;
> >  	enum umh_wait wait;
> >  	int retval;
> > -	struct file *stdin;
> >  	int (*init)(struct subprocess_info *info);
> >  	void (*cleanup)(struct subprocess_info *info);
> >  	void *data;
> > @@ -75,8 +74,6 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
> >  /* Set various pieces of state into the subprocess_info structure */
> >  void call_usermodehelper_setkeys(struct subprocess_info *info,
> >  				 struct key *session_keyring);
> > -int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
> > -				  struct file **filp);
> >  void call_usermodehelper_setfns(struct subprocess_info *info,
> >  		    int (*init)(struct subprocess_info *info),
> >  		    void (*cleanup)(struct subprocess_info *info),
> > @@ -132,10 +129,6 @@ call_usermodehelper_keys(char *path, char **argv, char **envp,
> >  
> >  extern void usermodehelper_init(void);
> >  
> > -struct file;
> > -extern int call_usermodehelper_pipe(char *path, char *argv[], char *envp[],
> > -				    struct file **filp);
> > -
> >  extern int usermodehelper_disable(void);
> >  extern void usermodehelper_enable(void);
> >  
> > diff --git a/kernel/kmod.c b/kernel/kmod.c
> > index 531ef62..d154454 100644
> > --- a/kernel/kmod.c
> > +++ b/kernel/kmod.c
> > @@ -147,23 +147,6 @@ static int ____call_usermodehelper(void *data)
> >  	commit_creds(sub_info->cred);
> >  	sub_info->cred = NULL;
> >  
> > -	/* Install input pipe when needed */
> > -	if (sub_info->stdin) {
> > -		struct files_struct *f = current->files;
> > -		struct fdtable *fdt;
> > -		/* no races because files should be private here */
> > -		sys_close(0);
> > -		fd_install(0, sub_info->stdin);
> > -		spin_lock(&f->file_lock);
> > -		fdt = files_fdtable(f);
> > -		FD_SET(0, fdt->open_fds);
> > -		FD_CLR(0, fdt->close_on_exec);
> > -		spin_unlock(&f->file_lock);
> > -
> > -		/* and disallow core files too */
> > -		current->signal->rlim[RLIMIT_CORE] = (struct rlimit){0, 0};
> > -	}
> > -
> >  	/* We can run anywhere, unlike our parent keventd(). */
> >  	set_cpus_allowed_ptr(current, cpu_all_mask);
> >  
> > @@ -429,35 +412,6 @@ void call_usermodehelper_setfns(struct subprocess_info *info,
> >  EXPORT_SYMBOL(call_usermodehelper_setfns);
> >  
> >  /**
> > - * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
> > - * @sub_info: a subprocess_info returned by call_usermodehelper_setup
> > - * @filp: set to the write-end of a pipe
> > - *
> > - * This constructs a pipe, and sets the read end to be the stdin of the
> > - * subprocess, and returns the write-end in *@...p.
> > - */
> > -int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
> > -				  struct file **filp)
> > -{
> > -	struct file *f;
> > -
> > -	f = create_write_pipe(0);
> > -	if (IS_ERR(f))
> > -		return PTR_ERR(f);
> > -	*filp = f;
> > -
> > -	f = create_read_pipe(f, 0);
> > -	if (IS_ERR(f)) {
> > -		free_write_pipe(*filp);
> > -		return PTR_ERR(f);
> > -	}
> > -	sub_info->stdin = f;
> > -
> > -	return 0;
> > -}
> > -EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
> > -
> > -/**
> >   * call_usermodehelper_exec - start a usermode application
> >   * @sub_info: information about the subprocessa
> >   * @wait: wait for the application to finish and return status.
> > @@ -504,42 +458,6 @@ unlock:
> >  }
> >  EXPORT_SYMBOL(call_usermodehelper_exec);
> >  
> > -/**
> > - * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
> > - * @path: path to usermode executable
> > - * @argv: arg vector for process
> > - * @envp: environment for process
> > - * @filp: set to the write-end of a pipe
> > - *
> > - * This is a simple wrapper which executes a usermode-helper function
> > - * with a pipe as stdin.  It is implemented entirely in terms of
> > - * lower-level call_usermodehelper_* functions.
> > - */
> > -int call_usermodehelper_pipe(char *path, char **argv, char **envp,
> > -			     struct file **filp)
> > -{
> > -	struct subprocess_info *sub_info;
> > -	int ret;
> > -
> > -	sub_info = call_usermodehelper_setup(path, argv, envp,
> > -					     GFP_KERNEL);
> > -	if (sub_info == NULL)
> > -		return -ENOMEM;
> > -
> > -	ret = call_usermodehelper_stdinpipe(sub_info, filp);
> > -	if (ret < 0) {
> > -		call_usermodehelper_freeinfo(sub_info);
> > -		return ret;
> > -	}
> > -
> > -	ret = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
> > -	if (ret < 0)	/* Failed to execute helper, close pipe */
> > -		filp_close(*filp, NULL);
> > -
> > -	return ret;
> > -}
> > -EXPORT_SYMBOL(call_usermodehelper_pipe);
> > -
> >  void __init usermodehelper_init(void)
> >  {
> >  	khelper_wq = create_singlethread_workqueue("khelper");
> 
> 
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