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Commit 2dab5974 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Fix possible filp_cachep memory corruption 



In commit 31e6b01f ("fs: rcu-walk for path lookup") we started doing
path lookup using RCU, which then falls back to a careful non-RCU lookup
in case of problems (LOOKUP_REVAL).  So do_filp_open() has this "re-do
the lookup carefully" looping case.

However, that means that we must not release the open-intent file data
if we are going to loop around and use it once more!

Fix this by moving the release of the open-intent data to the function
that allocates it (do_filp_open() itself) rather than the helper
functions that can get called multiple times (finish_open() and
do_last()).  This makes the logic for the lifetime of that field much
more obvious, and avoids the possible double free.

Reported-by: default avatarJ. R. Okajima <hooanon05@yahoo.co.jp>
Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d2478521

fs/namei.c

+10 −10
Original line number Diff line number Diff line
@@ -561,10 +561,14 @@ static inline int nameidata_drop_rcu_last_maybe(struct nameidata *nd) 
 */

void release_open_intent(struct nameidata *nd)

{

	if (nd->intent.open.file->f_path.dentry == NULL)

		put_filp(nd->intent.open.file);

	struct file *file = nd->intent.open.file;



	if (file && !IS_ERR(file)) {

		if (file->f_path.dentry == NULL)

			put_filp(file);

		else

		fput(nd->intent.open.file);

			fput(file);

	}

}



/*
@@ -2265,8 +2269,6 @@ static struct file *finish_open(struct nameidata *nd, 
	return filp;



exit:

	if (!IS_ERR(nd->intent.open.file))

		release_open_intent(nd);

	path_put(&nd->path);

	return ERR_PTR(error);

}
@@ -2389,8 +2391,6 @@ static struct file *do_last(struct nameidata *nd, struct path *path, 
exit_dput:

	path_put_conditional(path, nd);

exit:

	if (!IS_ERR(nd->intent.open.file))

		release_open_intent(nd);

	path_put(&nd->path);

	return ERR_PTR(error);

}
@@ -2477,6 +2477,7 @@ struct file *do_filp_open(int dfd, const char *pathname, 
	}

	audit_inode(pathname, nd.path.dentry);

	filp = finish_open(&nd, open_flag, acc_mode);

	release_open_intent(&nd);

	return filp;



creat:
@@ -2553,6 +2554,7 @@ struct file *do_filp_open(int dfd, const char *pathname, 
		path_put(&nd.root);

	if (filp == ERR_PTR(-ESTALE) && !(flags & LOOKUP_REVAL))

		goto reval;

	release_open_intent(&nd);

	return filp;



exit_dput:
@@ -2560,8 +2562,6 @@ struct file *do_filp_open(int dfd, const char *pathname, 
out_path:

	path_put(&nd.path);

out_filp:

	if (!IS_ERR(nd.intent.open.file))

		release_open_intent(&nd);

	filp = ERR_PTR(error);

	goto out;

}

fs/open.c

+2 −0
Original line number Diff line number Diff line
@@ -790,6 +790,8 @@ struct file *nameidata_to_filp(struct nameidata *nd) 


	/* Pick up the filp from the open intent */

	filp = nd->intent.open.file;

	nd->intent.open.file = NULL;



	/* Has the filesystem initialised the file for us? */

	if (filp->f_path.dentry == NULL) {

		path_get(&nd->path);