From: James Morris Prevent permission checking from being performed when the kernel wants to unconditionally remove a sysfs group, by introducing an kernel-only variant of lookup_one_len(), lookup_one_len_kern(). Additionally, as sysfs_remove_group() does not check the return value of the lookup before using it, a BUG_ON has been added to pinpoint the cause of any problems potentially caused by this (and as a form of annotation). Signed-off-by: James Morris Cc: Nagendra Singh Tomar Cc: Greg KH Cc: Tejun Heo Cc: Stephen Smalley Cc: Eric Paris Signed-off-by: Andrew Morton --- fs/namei.c | 72 ++++++++++++++++++++++++++++------------ fs/sysfs/group.c | 6 ++- include/linux/namei.h | 1 3 files changed, 57 insertions(+), 22 deletions(-) diff -puN fs/namei.c~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group fs/namei.c --- a/fs/namei.c~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group +++ a/fs/namei.c @@ -1243,22 +1243,13 @@ int __user_path_lookup_open(const char _ return err; } -/* - * Restricted form of lookup. Doesn't follow links, single-component only, - * needs parent already locked. Doesn't follow mounts. - * SMP-safe. - */ -static struct dentry * __lookup_hash(struct qstr *name, struct dentry * base, struct nameidata *nd) +static inline struct dentry *__lookup_hash_kern(struct qstr *name, struct dentry *base, struct nameidata *nd) { - struct dentry * dentry; + struct dentry *dentry; struct inode *inode; int err; inode = base->d_inode; - err = permission(inode, MAY_EXEC, nd); - dentry = ERR_PTR(err); - if (err) - goto out; /* * See if the low-level filesystem might want @@ -1287,35 +1278,76 @@ out: return dentry; } +/* + * Restricted form of lookup. Doesn't follow links, single-component only, + * needs parent already locked. Doesn't follow mounts. + * SMP-safe. + */ +static inline struct dentry * __lookup_hash(struct qstr *name, struct dentry *base, struct nameidata *nd) +{ + struct dentry *dentry; + struct inode *inode; + int err; + + inode = base->d_inode; + + err = permission(inode, MAY_EXEC, nd); + dentry = ERR_PTR(err); + if (err) + goto out; + + dentry = __lookup_hash_kern(name, base, nd); +out: + return dentry; +} + static struct dentry *lookup_hash(struct nameidata *nd) { return __lookup_hash(&nd->last, nd->dentry, nd); } /* SMP-safe */ -struct dentry * lookup_one_len(const char * name, struct dentry * base, int len) +static inline int __lookup_one_len(const char *name, struct qstr *this, struct dentry *base, int len) { unsigned long hash; - struct qstr this; unsigned int c; - this.name = name; - this.len = len; + this->name = name; + this->len = len; if (!len) - goto access; + return -EACCES; hash = init_name_hash(); while (len--) { c = *(const unsigned char *)name++; if (c == '/' || c == '\0') - goto access; + return -EACCES; hash = partial_name_hash(c, hash); } - this.hash = end_name_hash(hash); + this->hash = end_name_hash(hash); + return 0; +} +struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) +{ + int err; + struct qstr this; + + err = __lookup_one_len(name, &this, base, len); + if (err) + return ERR_PTR(err); return __lookup_hash(&this, base, NULL); -access: - return ERR_PTR(-EACCES); +} + +struct dentry *lookup_one_len_kern(const char *name, struct dentry *base, int len) +{ + int err; + struct qstr this; + + err = __lookup_one_len(name, &this, base, len); + if (err) + return ERR_PTR(err); + return __lookup_hash_kern(&this, base, NULL); } /* diff -puN fs/sysfs/group.c~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group fs/sysfs/group.c --- a/fs/sysfs/group.c~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group +++ a/fs/sysfs/group.c @@ -70,9 +70,11 @@ void sysfs_remove_group(struct kobject * { struct dentry * dir; - if (grp->name) - dir = lookup_one_len(grp->name, kobj->dentry, + if (grp->name) { + dir = lookup_one_len_kern(grp->name, kobj->dentry, strlen(grp->name)); + BUG_ON(IS_ERR(dir)); + } else dir = dget(kobj->dentry); diff -puN include/linux/namei.h~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group include/linux/namei.h --- a/include/linux/namei.h~security-prevent-permission-checking-of-file-removal-via-sysfs_remove_group +++ a/include/linux/namei.h @@ -82,6 +82,7 @@ extern struct file *nameidata_to_filp(st extern void release_open_intent(struct nameidata *); extern struct dentry * lookup_one_len(const char *, struct dentry *, int); +extern struct dentry *lookup_one_len_kern(const char *, struct dentry *, int); extern int follow_down(struct vfsmount **, struct dentry **); extern int follow_up(struct vfsmount **, struct dentry **); _