Add a new O_BENEATH flag for openat(2) which restricts the provided path, rejecting (with -EPERM) paths that are not beneath the provided dfd. In particular, reject: - paths that contain .. components - paths that begin with / - symlinks that have paths as above.
Also disallow use of nd_jump_link() for following symlinks without path expansion, when O_BENEATH is set. Signed-off-by: David Drysdale <[email protected]> --- arch/alpha/include/uapi/asm/fcntl.h | 1 + arch/parisc/include/uapi/asm/fcntl.h | 1 + arch/sparc/include/uapi/asm/fcntl.h | 1 + fs/fcntl.c | 4 ++-- fs/namei.c | 21 ++++++++++++++++++--- fs/open.c | 4 +++- fs/proc/base.c | 4 +++- fs/proc/namespaces.c | 8 ++++++-- include/linux/namei.h | 3 ++- include/uapi/asm-generic/fcntl.h | 4 ++++ 10 files changed, 41 insertions(+), 10 deletions(-) diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h index 09f49a6b87d1..76a87038d2c1 100644 --- a/arch/alpha/include/uapi/asm/fcntl.h +++ b/arch/alpha/include/uapi/asm/fcntl.h @@ -33,6 +33,7 @@ #define O_PATH 040000000 #define __O_TMPFILE 0100000000 +#define O_BENEATH 0200000000 /* no / or .. in openat path */ #define F_GETLK 7 #define F_SETLK 8 diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h index 34a46cbc76ed..3adadf72f929 100644 --- a/arch/parisc/include/uapi/asm/fcntl.h +++ b/arch/parisc/include/uapi/asm/fcntl.h @@ -21,6 +21,7 @@ #define O_PATH 020000000 #define __O_TMPFILE 040000000 +#define O_BENEATH 080000000 /* no / or .. in openat path */ #define F_GETLK64 8 #define F_SETLK64 9 diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h index 7e8ace5bf760..ea38f0bd6cec 100644 --- a/arch/sparc/include/uapi/asm/fcntl.h +++ b/arch/sparc/include/uapi/asm/fcntl.h @@ -36,6 +36,7 @@ #define O_PATH 0x1000000 #define __O_TMPFILE 0x2000000 +#define O_BENEATH 0x4000000 /* no / or .. in openat path */ #define F_GETOWN 5 /* for sockets. */ #define F_SETOWN 6 /* for sockets. */ diff --git a/fs/fcntl.c b/fs/fcntl.c index ee85cd4e136a..3169693e9390 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -740,7 +740,7 @@ static int __init fcntl_init(void) * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY * is defined as O_NONBLOCK on some platforms and not on others. */ - BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32( + BUILD_BUG_ON(22 - 1 /* for O_RDONLY being 0 */ != HWEIGHT32( O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | O_APPEND | /* O_NONBLOCK | */ @@ -748,7 +748,7 @@ static int __init fcntl_init(void) O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | O_NOATIME | O_CLOEXEC | __FMODE_EXEC | O_PATH | __O_TMPFILE | - __FMODE_NONOTIFY + __FMODE_NONOTIFY| O_BENEATH )); fasync_cache = kmem_cache_create("fasync_cache", diff --git a/fs/namei.c b/fs/namei.c index c83145af4bfc..67e9a8e27329 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -705,13 +705,16 @@ static inline void path_to_nameidata(const struct path *path, * Helper to directly jump to a known parsed path from ->follow_link, * caller must have taken a reference to path beforehand. */ -void nd_jump_link(struct nameidata *nd, struct path *path) +int nd_jump_link(struct nameidata *nd, struct path *path) { + if (nd->flags & LOOKUP_BENEATH) + return -EPERM; path_put(&nd->path); nd->path = *path; nd->inode = nd->path.dentry->d_inode; nd->flags |= LOOKUP_JUMPED; + return 0; } void nd_set_link(struct nameidata *nd, char *path) @@ -1775,9 +1778,14 @@ static int link_path_walk(const char *name, struct nameidata *nd) { struct path next; int err; - - while (*name=='/') + + while (*name == '/') { + if (nd->flags & LOOKUP_BENEATH) { + err = -EPERM; + goto exit; + } name++; + } if (!*name) return 0; @@ -1796,6 +1804,10 @@ static int link_path_walk(const char *name, struct nameidata *nd) if (name[0] == '.') switch (hashlen_len(hash_len)) { case 2: if (name[1] == '.') { + if (nd->flags & LOOKUP_BENEATH) { + err = -EPERM; + goto exit; + } type = LAST_DOTDOT; nd->flags |= LOOKUP_JUMPED; } @@ -1847,6 +1859,7 @@ static int link_path_walk(const char *name, struct nameidata *nd) break; } } +exit: terminate_walk(nd); return err; } @@ -1886,6 +1899,8 @@ static int path_init(int dfd, const char *name, unsigned int flags, nd->m_seq = read_seqbegin(&mount_lock); if (*name=='/') { + if (flags & LOOKUP_BENEATH) + return -EPERM; if (flags & LOOKUP_RCU) { rcu_read_lock(); nd->seq = set_root_rcu(nd); diff --git a/fs/open.c b/fs/open.c index 33f9cbf2610b..16e06610ddbb 100644 --- a/fs/open.c +++ b/fs/open.c @@ -902,7 +902,7 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o * If we have O_PATH in the open flag. Then we * cannot have anything other than the below set of flags */ - flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH; + flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH | O_BENEATH; acc_mode = 0; } else { acc_mode = MAY_OPEN | ACC_MODE(flags); @@ -933,6 +933,8 @@ static inline int build_open_flags(int flags, umode_t mode, struct open_flags *o lookup_flags |= LOOKUP_DIRECTORY; if (!(flags & O_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; + if (flags & O_BENEATH) + lookup_flags |= LOOKUP_BENEATH; op->lookup_flags = lookup_flags; return 0; } diff --git a/fs/proc/base.c b/fs/proc/base.c index 3f3d7aeb0712..eb8a9926ebb1 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1385,7 +1385,9 @@ static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd) if (error) goto out; - nd_jump_link(nd, &path); + error = nd_jump_link(nd, &path); + if (error) + goto out; return NULL; out: return ERR_PTR(error); diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c index c9eac4563fa8..8351534dc43b 100644 --- a/fs/proc/namespaces.c +++ b/fs/proc/namespaces.c @@ -36,6 +36,7 @@ static void *proc_ns_follow_link(struct dentry *dentry, struct nameidata *nd) const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops; struct task_struct *task; struct path ns_path; + int err; void *error = ERR_PTR(-EACCES); task = get_proc_task(inode); @@ -44,8 +45,11 @@ static void *proc_ns_follow_link(struct dentry *dentry, struct nameidata *nd) if (ptrace_may_access(task, PTRACE_MODE_READ)) { error = ns_get_path(&ns_path, task, ns_ops); - if (!error) - nd_jump_link(nd, &ns_path); + if (!error) { + err = nd_jump_link(nd, &ns_path); + if (err) + error = ERR_PTR(err); + } } put_task_struct(task); return error; diff --git a/include/linux/namei.h b/include/linux/namei.h index c8990779f0c3..bd656840a271 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -28,6 +28,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_FOLLOW 0x0001 #define LOOKUP_DIRECTORY 0x0002 #define LOOKUP_AUTOMOUNT 0x0004 +#define LOOKUP_BENEATH 0x0008 #define LOOKUP_PARENT 0x0010 #define LOOKUP_REVAL 0x0020 @@ -70,7 +71,7 @@ extern int follow_up(struct path *); extern struct dentry *lock_rename(struct dentry *, struct dentry *); extern void unlock_rename(struct dentry *, struct dentry *); -extern void nd_jump_link(struct nameidata *nd, struct path *path); +extern int nd_jump_link(struct nameidata *nd, struct path *path); extern void nd_set_link(struct nameidata *nd, char *path); extern char *nd_get_link(struct nameidata *nd); diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h index e063effe0cc1..4542bc6a2950 100644 --- a/include/uapi/asm-generic/fcntl.h +++ b/include/uapi/asm-generic/fcntl.h @@ -92,6 +92,10 @@ #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY) #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT) +#ifndef O_BENEATH +#define O_BENEATH 040000000 /* no / or .. in openat path */ +#endif + #ifndef O_NDELAY #define O_NDELAY O_NONBLOCK #endif -- 2.2.0.rc0.207.ga3a616c -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
