Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264764AbUDWItY (ORCPT ); Fri, 23 Apr 2004 04:49:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264766AbUDWItY (ORCPT ); Fri, 23 Apr 2004 04:49:24 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.101]:60346 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id S264764AbUDWIsw (ORCPT ); Fri, 23 Apr 2004 04:48:52 -0400 Date: Fri, 23 Apr 2004 14:22:18 +0530 From: Maneesh Soni To: viro@parcelfarce.linux.theplanet.co.uk Cc: Greg KH , Jeff Garzik , LKML Subject: Re: [RFC] fix sysfs symlinks Message-ID: <20040423085218.GB27638@in.ibm.com> Reply-To: maneesh@in.ibm.com References: <20040415220232.GC23039@kroah.com> <20040416152448.GF24997@parcelfarce.linux.theplanet.co.uk> <20040416223732.GC21701@kroah.com> <20040416234601.GL24997@parcelfarce.linux.theplanet.co.uk> <40807466.1020701@pobox.com> <20040417090712.B11481@flint.arm.linux.org.uk> <20040417082206.GM24997@parcelfarce.linux.theplanet.co.uk> <20040420161602.GB9603@kroah.com> <20040421101104.GA7921@in.ibm.com> <20040422213736.GL17014@parcelfarce.linux.theplanet.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040422213736.GL17014@parcelfarce.linux.theplanet.co.uk> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10243 Lines: 351 On Thu, Apr 22, 2004 at 10:37:37PM +0100, viro@parcelfarce.linux.theplanet.co.uk wrote: [..] > > I would unhash before doing kobject_put() here. Otherwise you are risking > ->follow_link() or ->readlink() coming between kobject_put() and unhashing, > which will screw you when sysfs_get_kobject() tries to grab a reference to > (already freed) ->d_fsdata. > > > + /* release the target kobject in case of > > + * a symlink > > + */ > > + if (S_ISLNK(victim->d_inode->i_mode)) > > + kobject_put(victim->d_fsdata); > > d_delete(victim); > > Ditto. Right.. I have corrected this. [..] > > Huh? Not to mention anything else, dput(d) is guaranteed to screw you if > IS_ERR(d) is true. great eyes.. I couldn't spot this even with four eyes 8-).. but for my relief I was not the culprit for this. I also corrected a couple of more uses of sysfs_get_dentry(). > > + down(&target_parent->d_inode->i_sem); > > + error = sysfs_get_target_path(kobj, target_kobj, path); > > + up(&target_parent->d_inode->i_sem); > > You need to be careful in sysfs_get_target_path() - this ->i_sem doesn't > prevent renames of ancestors. rwsem held exclusive by renaming and shared > by sysfs_get_target_path(), maybe? FWIW, even rwlock might be sufficient... I used rwsem, considering the allocations done in kobject_set_name(). Updated patch appended. Thanks Maneesh o The symlinks code in sysfs doesnot point to the correct target kobject whenever target kobject is renamed and suffers from dangling symlinks if target kobject is removed. o The following patch implements ->readlink and ->follow_link operations for sysfs instead of using the page_symlink_inode_operations. The pointer to target kobject is saved in the link dentry's d_fsdata field. The target path is generated everytime we do ->readlink and ->follow_link. This results in generating the correct target path during readlink and follow_link operations inspite of renamed target kobject. o This also pins the target kobject during link creation and the ref. is released when the link is removed. o Apart from being correct this patch also saves some memory by not pinning a whole page for saving the target information. o Used a rw_semaphor sysfs_rename_sem to avoid clashing with renaming of ancestors while the target path is generated. o Also corrected a couple of sysfs_get_dentry() uses. fs/sysfs/dir.c | 17 +++++- fs/sysfs/group.c | 12 ++-- fs/sysfs/inode.c | 5 + fs/sysfs/symlink.c | 136 +++++++++++++++++++++++++++++++++++++---------------- fs/sysfs/sysfs.h | 3 + 5 files changed, 124 insertions(+), 49 deletions(-) diff -puN fs/sysfs/sysfs.h~sysfs-symlinks-fix fs/sysfs/sysfs.h --- linux-2.6.6-rc2-mm1/fs/sysfs/sysfs.h~sysfs-symlinks-fix 2004-04-23 10:22:41.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/sysfs.h 2004-04-23 12:11:52.000000000 +0530 @@ -12,6 +12,9 @@ extern void sysfs_hash_and_remove(struct extern int sysfs_create_subdir(struct kobject *, const char *, struct dentry **); extern void sysfs_remove_subdir(struct dentry *); +extern int sysfs_readlink(struct dentry *, char __user *, int ); +extern int sysfs_follow_link(struct dentry *, struct nameidata *); +extern struct rw_semaphore sysfs_rename_sem; static inline struct kobject *sysfs_get_kobject(struct dentry *dentry) { diff -puN fs/sysfs/dir.c~sysfs-symlinks-fix fs/sysfs/dir.c --- linux-2.6.6-rc2-mm1/fs/sysfs/dir.c~sysfs-symlinks-fix 2004-04-23 10:22:41.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/dir.c 2004-04-23 11:30:17.000000000 +0530 @@ -10,6 +10,8 @@ #include #include "sysfs.h" +DECLARE_RWSEM(sysfs_rename_sem); + static int init_dir(struct inode * inode) { inode->i_op = &simple_dir_inode_operations; @@ -136,6 +138,12 @@ restart: */ spin_unlock(&dcache_lock); d_delete(d); + /* release the target kobject in case of + * a symlink + */ + if (S_ISLNK(d->d_inode->i_mode)) + kobject_put(d->d_fsdata); + simple_unlink(dentry->d_inode,d); dput(d); pr_debug(" done\n"); @@ -167,10 +175,13 @@ void sysfs_rename_dir(struct kobject * k parent = kobj->parent->dentry; down(&parent->d_inode->i_sem); - new_dentry = sysfs_get_dentry(parent, new_name); - d_move(kobj->dentry, new_dentry); - kobject_set_name(kobj,new_name); + if (!IS_ERR(new_dentry)) { + down_write(&sysfs_rename_sem); + d_move(kobj->dentry, new_dentry); + kobject_set_name(kobj,new_name); + up_write(&sysfs_rename_sem); + } up(&parent->d_inode->i_sem); } diff -puN fs/sysfs/inode.c~sysfs-symlinks-fix fs/sysfs/inode.c --- linux-2.6.6-rc2-mm1/fs/sysfs/inode.c~sysfs-symlinks-fix 2004-04-23 10:22:41.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/inode.c 2004-04-23 11:03:38.000000000 +0530 @@ -97,6 +97,11 @@ void sysfs_hash_and_remove(struct dentry atomic_read(&victim->d_count)); d_delete(victim); + /* release the target kobject in case of + * a symlink + */ + if (S_ISLNK(victim->d_inode->i_mode)) + kobject_put(victim->d_fsdata); simple_unlink(dir->d_inode,victim); } /* diff -puN fs/sysfs/symlink.c~sysfs-symlinks-fix fs/sysfs/symlink.c --- linux-2.6.6-rc2-mm1/fs/sysfs/symlink.c~sysfs-symlinks-fix 2004-04-23 10:22:41.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/symlink.c 2004-04-23 11:40:49.000000000 +0530 @@ -8,27 +8,17 @@ #include "sysfs.h" +static struct inode_operations sysfs_symlink_inode_operations = { + .readlink = sysfs_readlink, + .follow_link = sysfs_follow_link, +}; static int init_symlink(struct inode * inode) { - inode->i_op = &page_symlink_inode_operations; + inode->i_op = &sysfs_symlink_inode_operations; return 0; } -static int sysfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname) -{ - int error; - - error = sysfs_create(dentry, S_IFLNK|S_IRWXUGO, init_symlink); - if (!error) { - int l = strlen(symname)+1; - error = page_symlink(dentry->d_inode, symname, l); - if (error) - iput(dentry->d_inode); - } - return error; -} - static int object_depth(struct kobject * kobj) { struct kobject * p = kobj; @@ -74,37 +64,20 @@ int sysfs_create_link(struct kobject * k struct dentry * dentry = kobj->dentry; struct dentry * d; int error = 0; - int size; - int depth; - char * path; - char * s; - - depth = object_depth(kobj); - size = object_path_length(target) + depth * 3 - 1; - if (size > PATH_MAX) - return -ENAMETOOLONG; - pr_debug("%s: depth = %d, size = %d\n",__FUNCTION__,depth,size); - - path = kmalloc(size,GFP_KERNEL); - if (!path) - return -ENOMEM; - memset(path,0,size); - - for (s = path; depth--; s += 3) - strcpy(s,"../"); - - fill_object_path(target,path,size); - pr_debug("%s: path = '%s'\n",__FUNCTION__,path); down(&dentry->d_inode->i_sem); d = sysfs_get_dentry(dentry,name); - if (!IS_ERR(d)) - error = sysfs_symlink(dentry->d_inode,d,path); - else + if (!IS_ERR(d)) { + error = sysfs_create(d, S_IFLNK|S_IRWXUGO, init_symlink); + if (!error) + /* + * associate the link dentry with the target kobject + */ + d->d_fsdata = kobject_get(target); + dput(d); + } else error = PTR_ERR(d); - dput(d); up(&dentry->d_inode->i_sem); - kfree(path); return error; } @@ -120,6 +93,87 @@ void sysfs_remove_link(struct kobject * sysfs_hash_and_remove(kobj->dentry,name); } +static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target, + char *path) +{ + char * s; + int depth, size; + + depth = object_depth(kobj); + size = object_path_length(target) + depth * 3 - 1; + if (size > PATH_MAX) + return -ENAMETOOLONG; + + pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size); + + for (s = path; depth--; s += 3) + strcpy(s,"../"); + + fill_object_path(target, path, size); + pr_debug("%s: path = '%s'\n", __FUNCTION__, path); + + return 0; +} + +static int sysfs_getlink(struct dentry *dentry, char * path) +{ + struct kobject *kobj, *target_kobj; + struct dentry * target_parent; + int error = 0; + + kobj = sysfs_get_kobject(dentry->d_parent); + if (!kobj) + return -EINVAL; + + target_kobj = sysfs_get_kobject(dentry); + if (!target_kobj) { + kobject_put(kobj); + return -EINVAL; + } + + down_read(&sysfs_rename_sem); + error = sysfs_get_target_path(kobj, target_kobj, path); + up_read(&sysfs_rename_sem); + + kobject_put(kobj); + kobject_put(target_kobj); + return error; + +} + +int sysfs_readlink(struct dentry *dentry, char __user *buffer, int buflen) +{ + int error = 0; + unsigned long page = get_zeroed_page(GFP_KERNEL); + + if (!page) + return -ENOMEM; + + error = sysfs_getlink(dentry, (char *) page); + if (!error) + error = vfs_readlink(dentry, buffer, buflen, (char *) page); + + free_page(page); + + return error; +} + +int sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) +{ + int error = 0; + unsigned long page = get_zeroed_page(GFP_KERNEL); + + if (!page) + return -ENOMEM; + + error = sysfs_getlink(dentry, (char *) page); + if (!error) + error = vfs_follow_link(nd, (char *) page); + + free_page(page); + + return error; +} EXPORT_SYMBOL(sysfs_create_link); EXPORT_SYMBOL(sysfs_remove_link); diff -puN fs/sysfs/group.c~sysfs-symlinks-fix fs/sysfs/group.c --- linux-2.6.6-rc2-mm1/fs/sysfs/group.c~sysfs-symlinks-fix 2004-04-23 11:20:40.000000000 +0530 +++ linux-2.6.6-rc2-mm1-maneesh/fs/sysfs/group.c 2004-04-23 11:22:12.000000000 +0530 @@ -70,11 +70,13 @@ void sysfs_remove_group(struct kobject * else dir = dget(kobj->dentry); - remove_files(dir,grp); - if (grp->name) - sysfs_remove_subdir(dir); - /* release the ref. taken in this routine */ - dput(dir); + if (dir && !IS_ERR(dir)) { + remove_files(dir,grp); + if (grp->name) + sysfs_remove_subdir(dir); + /* release the ref. taken in this routine */ + dput(dir); + } } _ -- Maneesh Soni Linux Technology Center, IBM Software Lab, Bangalore, India email: maneesh@in.ibm.com Phone: 91-80-25044999 Fax: 91-80-25268553 T/L : 9243696 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/