Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965433AbbEEFcf (ORCPT ); Tue, 5 May 2015 01:32:35 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:40079 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755638AbbEEFXI (ORCPT ); Tue, 5 May 2015 01:23:08 -0400 From: Al Viro To: Linus Torvalds Cc: Neil Brown , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 79/79] namei: stretch RCU mode into get_link() Date: Tue, 5 May 2015 06:22:53 +0100 Message-Id: <1430803373-4948-79-git-send-email-viro@ZenIV.linux.org.uk> X-Mailer: git-send-email 1.7.7.6 In-Reply-To: <20150505052205.GS889@ZenIV.linux.org.uk> References: <20150505052205.GS889@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5538 Lines: 201 From: Al Viro one potentially subtle point: may_follow_link() kludge rejecting symlink traversal in RCU mode is handled by returning -ECHILD and repeating everything in non-RCU mode. Reason: audit_log_link_denied() won't work in RCU mode. Signed-off-by: Al Viro --- fs/namei.c | 86 ++++++++++++++++++++++++++++++++++---------------------------- 1 file changed, 47 insertions(+), 39 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index cf8f2de..761d4b1 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -725,6 +725,29 @@ static int complete_walk(struct nameidata *nd) return status; } +static inline void put_link(struct nameidata *nd) +{ + struct saved *last = nd->stack + --nd->depth; + struct inode *inode = last->link.dentry->d_inode; + if (last->cookie && inode->i_op->put_link) + inode->i_op->put_link(last->link.dentry, last->cookie); + path_put(&last->link); +} + +static void terminate_walk(struct nameidata *nd) +{ + if (!(nd->flags & LOOKUP_RCU)) { + path_put(&nd->path); + } else { + nd->flags &= ~LOOKUP_RCU; + if (!(nd->flags & LOOKUP_ROOT)) + nd->root.mnt = NULL; + rcu_read_unlock(); + } + while (unlikely(nd->depth)) + put_link(nd); +} + static __always_inline void set_root(struct nameidata *nd) { get_fs_root(current->fs, &nd->root); @@ -776,15 +799,6 @@ void nd_jump_link(struct path *path) nd->flags |= LOOKUP_JUMPED; } -static inline void put_link(struct nameidata *nd) -{ - struct saved *last = nd->stack + --nd->depth; - struct inode *inode = last->link.dentry->d_inode; - if (last->cookie && inode->i_op->put_link) - inode->i_op->put_link(last->link.dentry, last->cookie); - path_put(&last->link); -} - int sysctl_protected_symlinks __read_mostly = 0; int sysctl_protected_hardlinks __read_mostly = 0; @@ -804,21 +818,20 @@ int sysctl_protected_hardlinks __read_mostly = 0; * * Returns 0 if following the symlink is allowed, -ve on error. */ -static inline int may_follow_link(struct path *link, struct nameidata *nd) +static inline int may_follow_link(struct path *link, const struct inode *inode, + struct nameidata *nd) { - const struct inode *inode; const struct inode *parent; if (!sysctl_protected_symlinks) return 0; /* Allowed if owner and follower match. */ - inode = link->dentry->d_inode; if (uid_eq(current_cred()->fsuid, inode->i_uid)) return 0; /* Allowed if parent directory not sticky and world-writable. */ - parent = nd->path.dentry->d_inode; + parent = nd->inode; if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH)) return 0; @@ -826,9 +839,14 @@ static inline int may_follow_link(struct path *link, struct nameidata *nd) if (uid_eq(parent->i_uid, inode->i_uid)) return 0; + if (nd->flags & LOOKUP_RCU) { + terminate_walk(nd); + return -ECHILD; + } + audit_log_link_denied("follow_link", link); - path_put_conditional(link, nd); - path_put(&nd->path); + path_to_nameidata(link, nd); + terminate_walk(nd); return -EACCES; } @@ -902,15 +920,19 @@ static int may_linkat(struct path *link) } static __always_inline -const char *get_link(struct nameidata *nd) +const char *get_link(struct nameidata *nd, struct inode *inode) { struct saved *last = nd->stack + nd->depth; struct dentry *dentry = nd->link.dentry; - struct inode *inode = dentry->d_inode; int error; const char *res; - BUG_ON(nd->flags & LOOKUP_RCU); + if (nd->flags & LOOKUP_RCU) { + if (unlikely(nd->link.mnt != nd->path.mnt || + unlazy_walk(nd, dentry))) { + return ERR_PTR(-ECHILD); + } + } if (nd->link.mnt == nd->path.mnt) mntget(nd->link.mnt); @@ -1553,20 +1575,6 @@ static inline int handle_dots(struct nameidata *nd, int type) return 0; } -static void terminate_walk(struct nameidata *nd) -{ - if (!(nd->flags & LOOKUP_RCU)) { - path_put(&nd->path); - } else { - nd->flags &= ~LOOKUP_RCU; - if (!(nd->flags & LOOKUP_ROOT)) - nd->root.mnt = NULL; - rcu_read_unlock(); - } - while (unlikely(nd->depth)) - put_link(nd); -} - static int pick_link(struct nameidata *nd, struct path *link) { int error; @@ -1847,16 +1855,16 @@ OK: if (err) { const char *s; + struct inode *inode = nd->link.dentry->d_inode; if (nd->flags & LOOKUP_RCU) { - if (unlikely(nd->link.mnt != nd->path.mnt || - unlazy_walk(nd, nd->link.dentry))) { + if (unlikely(is_stale(nd, nd->link.dentry))) { err = -ECHILD; break; } } - s = get_link(nd); + s = get_link(nd, inode); if (unlikely(IS_ERR(s))) { err = PTR_ERR(s); @@ -2009,20 +2017,20 @@ static void path_cleanup(struct nameidata *nd) static int trailing_symlink(struct nameidata *nd) { const char *s; + struct inode *inode = nd->link.dentry->d_inode; int error; if (nd->flags & LOOKUP_RCU) { - if (unlikely(nd->link.mnt != nd->path.mnt || - unlazy_walk(nd, nd->link.dentry))) { + if (unlikely(is_stale(nd, nd->link.dentry))) { terminate_walk(nd); return -ECHILD; } } - error = may_follow_link(&nd->link, nd); + error = may_follow_link(&nd->link, inode, nd); if (unlikely(error)) return error; nd->flags |= LOOKUP_PARENT; - s = get_link(nd); + s = get_link(nd, inode); if (unlikely(IS_ERR(s))) { terminate_walk(nd); return PTR_ERR(s); -- 2.1.4 -- 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/