From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: [PATCH review 2/4] vfs: Test for and handle paths that are unreachable from their mnt_root Date: Wed, 08 Apr 2015 18:32:58 -0500 Message-ID: <87sica8ac5.fsf_-_@x220.int.ebiederm.org> References: <871tncuaf6.fsf@x220.int.ebiederm.org> <87mw5xq7lt.fsf@x220.int.ebiederm.org> <87a8yqou41.fsf_-_@x220.int.ebiederm.org> <874moq9oyb.fsf_-_@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <874moq9oyb.fsf_-_-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org> (Eric W. Biederman's message of "Wed, 08 Apr 2015 18:31:56 -0500") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Linux Containers Cc: Andrey Vagin , Richard Weinberger , Andy Lutomirski , Al Viro , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jann Horn , Willy Tarreau List-Id: containers.vger.kernel.org - Add a dentry flag DCACHE_MOUNT_VIOLATED to mark loopback mounts that have had a dentry moved into a directory that does not descend from the mount root dentry. - In mnt_put_root clear DCACHE_MOUNT_VIOLATED. - Add a function path_connected to verify a path.dentry is reachable from path.mnt.mnt_root. AKA rename did not do something nasty to the bind mount. - Disable ".." when a path is not connected during lookup. (Maybe we want to stop ".." at this path instead?) Following .. is not disabled after a transition to / and is never disabled when / is the directory we start with. Because we already limit .. no higher than / - In prepend_path and it's callers in the d_path family for a path that is not connected don't attempt to find parent directories. Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Signed-off-by: "Eric W. Biederman" --- fs/dcache.c | 3 +++ fs/internal.h | 1 + fs/namei.c | 30 ++++++++++++++++++++++++++++++ fs/namespace.c | 2 +- include/linux/dcache.h | 6 ++++++ include/linux/namei.h | 2 ++ 6 files changed, 43 insertions(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index c71e3732e53b..e07eb03f6de6 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2871,6 +2871,9 @@ static int prepend_path(const struct path *path, char *bptr; int blen; + if (!path_connected(path)) + root = path; + rcu_read_lock(); restart_mnt: read_seqbegin_or_lock(&mount_lock, &m_seq); diff --git a/fs/internal.h b/fs/internal.h index 01dce1d1476b..046767f0042e 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -51,6 +51,7 @@ extern void __init chrdev_init(void); extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *); extern int vfs_path_lookup(struct dentry *, struct vfsmount *, const char *, unsigned int, struct path *); +extern bool path_connected(const struct path *); /* * namespace.c diff --git a/fs/namei.c b/fs/namei.c index c83145af4bfc..83cdcdf36eed 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -493,6 +493,22 @@ void path_put(const struct path *path) } EXPORT_SYMBOL(path_put); +/** + * path_connected - Verify that a path->dentry is below path->mnt->mnt.mnt_root + * @path: path to verify + * + * Rename can sometimes move a file or directory outside of bind mount + * don't honor paths where this has happened. + */ +bool path_connected(const struct path *path) +{ + struct dentry *root = path->mnt->mnt_root; + if (!d_mount_violated(root)) + return true; + + return is_subdir(path->dentry, root); +} + struct nameidata { struct path path; struct qstr last; @@ -712,6 +728,7 @@ void nd_jump_link(struct nameidata *nd, struct path *path) nd->path = *path; nd->inode = nd->path.dentry->d_inode; nd->flags |= LOOKUP_JUMPED; + nd->flags &= ~LOOKUP_NODOTDOT; } void nd_set_link(struct nameidata *nd, char *path) @@ -897,6 +914,7 @@ follow_link(struct path *link, struct nameidata *nd, void **p) nd->path = nd->root; path_get(&nd->root); nd->flags |= LOOKUP_JUMPED; + nd->flags &= ~LOOKUP_NODOTDOT; } nd->inode = nd->path.dentry->d_inode; error = link_path_walk(s, nd); @@ -1161,6 +1179,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, path->mnt = &mounted->mnt; path->dentry = mounted->mnt.mnt_root; nd->flags |= LOOKUP_JUMPED; + nd->flags &= ~LOOKUP_NODOTDOT; nd->seq = read_seqcount_begin(&path->dentry->d_seq); /* * Update the inode too. We don't need to re-check the @@ -1176,6 +1195,10 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, static int follow_dotdot_rcu(struct nameidata *nd) { struct inode *inode = nd->inode; + + if (nd->flags & LOOKUP_NODOTDOT) + return 0; + if (!nd->root.mnt) set_root_rcu(nd); @@ -1293,6 +1316,9 @@ static void follow_mount(struct path *path) static void follow_dotdot(struct nameidata *nd) { + if (nd->flags & LOOKUP_NODOTDOT) + return; + if (!nd->root.mnt) set_root(nd); @@ -1909,6 +1935,8 @@ static int path_init(int dfd, const char *name, unsigned int flags, } else { get_fs_pwd(current->fs, &nd->path); } + if (unlikely(!path_connected(&nd->path))) + nd->flags |= LOOKUP_NODOTDOT; } else { /* Caller must check execute permissions on the starting path component */ struct fd f = fdget_raw(dfd); @@ -1936,6 +1964,8 @@ static int path_init(int dfd, const char *name, unsigned int flags, path_get(&nd->path); fdput(f); } + if (unlikely(!path_connected(&nd->path))) + nd->flags |= LOOKUP_NODOTDOT; } nd->inode = nd->path.dentry->d_inode; diff --git a/fs/namespace.c b/fs/namespace.c index 0b517f1e898a..75abc9fcaafa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -850,7 +850,7 @@ static void mnt_put_root(struct mount *mnt) if (!--mr->r_count) { hlist_del(&mr->r_hash); spin_lock(&root->d_lock); - root->d_flags &= ~DCACHE_MOUNTROOT; + root->d_flags &= ~(DCACHE_MOUNTROOT | DCACHE_MOUNT_VIOLATED); spin_unlock(&root->d_lock); kfree(mr); } diff --git a/include/linux/dcache.h b/include/linux/dcache.h index 01cd930bf9d8..18e36d974168 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -227,6 +227,7 @@ struct dentry_operations { #define DCACHE_FALLTHRU 0x01000000 /* Fall through to lower layer */ #define DCACHE_MOUNTROOT 0x02000000 /* Root of a vfsmount */ +#define DCACHE_MOUNT_VIOLATED 0x04000000 /* Vfsmount with dentries moved out */ extern seqlock_t rename_lock; @@ -408,6 +409,11 @@ static inline bool d_mountroot(const struct dentry *dentry) return dentry->d_flags & DCACHE_MOUNTROOT; } +static inline bool d_mount_violated(const struct dentry *dentry) +{ + return dentry->d_flags & DCACHE_MOUNT_VIOLATED; +} + /* * Directory cache entry type accessor functions. */ diff --git a/include/linux/namei.h b/include/linux/namei.h index c8990779f0c3..55c8aaec7b03 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -45,6 +45,8 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_ROOT 0x2000 #define LOOKUP_EMPTY 0x4000 +#define LOOKUP_NODOTDOT 0x10000 + extern int user_path_at(int, const char __user *, unsigned, struct path *); extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty); -- 2.2.1