[PATCH 1/3 v2] namei: add LOOKUP_DFD_ROOT to use dfd as root
From: Andrey Vagin <hidden>
Date: 2016-07-05 21:27:27
Also in:
lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
The problem is that a pathname can contain absolute symlinks and now they are resolved relative to the current root. If we want to open a file in another mount namespaces and we have a file descriptor to its root directory, we probably want to resolve pathname in the target mount namespace. For this we add this new flag. If LOOKUP_DFD_ROOT is set, path_init() initializes nd->root and nd->path to the same value. Changes since v1: * initialize nd->root_seq (thanks to Omar Sandoval for reporting and fixing this issue) Cc: Omar Sandoval <osandov@osandov.com> Signed-off-by: Andrey Vagin <redacted> --- fs/namei.c | 16 +++++++++++++++- include/linux/namei.h | 2 ++ 2 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/fs/namei.c b/fs/namei.c
index 70580ab..d52541a 100644
--- a/fs/namei.c
+++ b/fs/namei.c@@ -2148,7 +2148,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->path.dentry = NULL; nd->m_seq = read_seqbegin(&mount_lock); - if (*s == '/') { + if (*s == '/' && !(flags & LOOKUP_DFD_ROOT)) { if (flags & LOOKUP_RCU) rcu_read_lock(); set_root(nd);
@@ -2174,6 +2174,13 @@ static const char *path_init(struct nameidata *nd, unsigned flags) get_fs_pwd(current->fs, &nd->path); nd->inode = nd->path.dentry->d_inode; } + if (flags & LOOKUP_DFD_ROOT) { + nd->root = nd->path; + if (flags & LOOKUP_RCU) + nd->root_seq = nd->seq; + else + path_get(&nd->root); + } return s; } else { /* Caller must check execute permissions on the starting path component */
@@ -2202,6 +2209,13 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->inode = nd->path.dentry->d_inode; } fdput(f); + if (flags & LOOKUP_DFD_ROOT) { + nd->root = nd->path; + if (flags & LOOKUP_RCU) + nd->root_seq = nd->seq; + else + path_get(&nd->root); + } return s; } }
diff --git a/include/linux/namei.h b/include/linux/namei.h
index d3d0398..ca2ea13 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_DFD_ROOT 0x8000 + extern int path_pts(struct path *path); extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty);
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2.5.5