All of lore.kernel.org
 help / color / mirror / Atom feed
From: NeilBrown <neilb@suse.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 14/20] VFS/namei: add 'inode' arg to put_link().
Date: Mon, 23 Mar 2015 13:37:40 +1100	[thread overview]
Message-ID: <20150323023740.8161.51849.stgit@notabene.brown> (raw)
In-Reply-To: <20150323023258.8161.32467.stgit@notabene.brown>

When symlinks are followed in RCU-walk, dentry->d_inode
may have changed between the call to ->follow_link and
the call to ->put_link.
So we need to preserve the inode used in the first instance,
and use it to find the correct put_link.

Note that this means that when RCU-walk is permitted in
->follow_link, dentry->d_inode cannot be used in ->put_link.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 Documentation/filesystems/porting |    4 ++++
 fs/namei.c                        |   20 ++++++++++++--------
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index eba8dd0a13e3..09454610515c 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -490,3 +490,7 @@ in your dentry operations instead.
 	The passed inode must be used rather than dentry->d_inode,
 	particularly if LOOKUP_RCU is set.
 	If s_fs_info is used, it must be freed using RCU.
+--
+[mandatory]
+	If ->follow_link permits RCU-walk, then ->put_link must
+	not access dentry->d_inode as that may have changed.
diff --git a/fs/namei.c b/fs/namei.c
index 224b1495edae..72f5a4f91855 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -763,9 +763,9 @@ static void terminate_walk(struct nameidata *nd)
 	}
 }
 
-static inline void put_link(struct nameidata *nd, struct path *link, void *cookie)
+static inline void put_link(struct nameidata *nd, struct path *link,
+			    struct inode *inode, void *cookie)
 {
-	struct inode *inode = link->dentry->d_inode;
 	if (inode->i_op->put_link)
 		inode->i_op->put_link(link->dentry, nd_get_link(nd), cookie);
 	if (!(nd->flags & LOOKUP_LINK_RCU))
@@ -934,7 +934,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 	if (s) {
 		if (unlikely(IS_ERR(s))) {
 			terminate_walk(nd);
-			put_link(nd, link, *p);
+			put_link(nd, link, inode, *p);
 			return PTR_ERR(s);
 		}
 		if (*s == '/') {
@@ -948,7 +948,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
 		nd->inode = nd->path.dentry->d_inode;
 		error = link_path_walk(s, nd);
 		if (unlikely(error))
-			put_link(nd, link, *p);
+			put_link(nd, link, inode, *p);
 	}
 
 	return error;
@@ -1669,13 +1669,14 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
 
 	do {
 		struct path link = *path;
+		struct inode *inode = link.dentry->d_inode;
 		void *cookie;
 
 		res = follow_link(&link, nd, &cookie);
 		if (res)
 			break;
 		res = walk_component(nd, path, LOOKUP_FOLLOW);
-		put_link(nd, &link, cookie);
+		put_link(nd, &link, inode, cookie);
 	} while (res > 0);
 
 	nd->link_count--;
@@ -2036,6 +2037,7 @@ static int path_lookupat(int dfd, const char *name,
 		while (err > 0) {
 			void *cookie;
 			struct path link = path;
+			struct inode *inode = link.dentry->d_inode;
 			err = may_follow_link(&link, nd);
 			if (unlikely(err))
 				break;
@@ -2044,7 +2046,7 @@ static int path_lookupat(int dfd, const char *name,
 			if (err)
 				break;
 			err = lookup_last(nd, &path);
-			put_link(nd, &link, cookie);
+			put_link(nd, &link, inode, cookie);
 		}
 	}
 
@@ -2396,6 +2398,7 @@ path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags
 	while (err > 0) {
 		void *cookie;
 		struct path link = *path;
+		struct inode *inode = link.dentry->d_inode;
 		err = may_follow_link(&link, &nd);
 		if (unlikely(err))
 			break;
@@ -2404,7 +2407,7 @@ path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags
 		if (err)
 			break;
 		err = mountpoint_last(&nd, path);
-		put_link(&nd, &link, cookie);
+		put_link(&nd, &link, inode, cookie);
 	}
 out:
 	path_cleanup(&nd);
@@ -3281,6 +3284,7 @@ static struct file *path_openat(int dfd, struct filename *pathname,
 	error = do_last(nd, &path, file, op, &opened, pathname);
 	while (unlikely(error > 0)) { /* trailing symlink */
 		struct path link = path;
+		struct inode *inode = link.dentry->d_inode;
 		void *cookie;
 		if (!(nd->flags & LOOKUP_FOLLOW)) {
 			path_to_nameidata(&path, nd);
@@ -3297,7 +3301,7 @@ static struct file *path_openat(int dfd, struct filename *pathname,
 		if (unlikely(error))
 			break;
 		error = do_last(nd, &path, file, op, &opened, pathname);
-		put_link(nd, &link, cookie);
+		put_link(nd, &link, inode, cookie);
 	}
 out:
 	path_cleanup(nd);



  parent reply	other threads:[~2015-03-23  2:39 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-23  2:37 [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown
2015-03-23  2:37 ` [PATCH 02/20] STAGING/lustre: limit follow_link recursion using stack space NeilBrown
2015-04-18  3:01   ` Al Viro
2015-04-19 20:57     ` Andreas Dilger
2015-04-19 21:33       ` Al Viro
2015-04-20  2:29         ` Al Viro
2015-03-23  2:37 ` [PATCH 03/20] VFS: replace {, total_}link_count in task_struct with pointer to nameidata NeilBrown
2015-03-23  2:37 ` [PATCH 01/20] Documentation: remove outdated information from automount-support.txt NeilBrown
2015-03-23  2:37 ` [PATCH 10/20] security: make inode_follow_link RCU-walk aware NeilBrown
2015-03-23  2:37 ` [PATCH 04/20] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link NeilBrown
2015-03-23  2:37 ` [PATCH 07/20] VFS: remove nameidata args from ->follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 06/20] SECURITY: remove nameidata arg from inode_follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 05/20] VFS: replace nameidata arg to ->put_link with a char* NeilBrown
2015-03-23  2:37 ` [PATCH 09/20] security/selinux: pass 'flags' arg to avc_audit() and avc_has_perm_flags() NeilBrown
2015-03-23  2:37 ` [PATCH 11/20] VFS/namei: use terminate_walk when symlink lookup fails NeilBrown
2015-03-23  2:37 ` [PATCH 08/20] VFS: make all ->follow_link handlers aware for LOOKUP_RCU NeilBrown
2015-03-23  2:37 ` [PATCH 13/20] VFS/namei: abort RCU-walk on symlink if atime needs updating NeilBrown
2015-03-23  2:37 ` NeilBrown [this message]
2015-04-17 16:25   ` [PATCH 14/20] VFS/namei: add 'inode' arg to put_link() Al Viro
2015-04-17 19:09     ` Al Viro
2015-04-18  8:09       ` Al Viro
2015-03-23  2:37 ` [PATCH 16/20] VFS/namei: enable RCU-walk when following symlinks NeilBrown
2015-03-23  2:37 ` [PATCH 19/20] XFS: allow follow_link to often succeed in RCU-walk NeilBrown
2015-03-23  2:37 ` [PATCH 20/20] NFS: support LOOKUP_RCU in nfs_follow_link NeilBrown
2015-03-23  2:37 ` [PATCH 18/20] xfs: use RCU to free 'struct xfs_mount' NeilBrown
2015-03-23  2:37 ` [PATCH 17/20] VFS/namei: handle LOOKUP_RCU in page_follow_link_light NeilBrown
2015-03-23  2:37 ` [PATCH 12/20] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU NeilBrown
2015-03-23  2:37 ` [PATCH 15/20] VFS/namei: enhance follow_link to support RCU-walk NeilBrown
2015-03-25 23:23 ` [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150323023740.8161.51849.stgit@notabene.brown \
    --to=neilb@suse.de \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=viro@ZenIV.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.