[PATCH -V16 04/12] vfs: Allow handle based open on symlinks
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From: Aneesh Kumar K.V on 12 Jul 2010 02:40 The patch update may_open to allow handle based open on symlinks. The file handle based API use file descritor returned from open_by_handle_at to do different file system operations. To find the link target name we need to get a file descriptor on symlinks. We should be able to read the link target using file handle. The exact usecase is with respect to implementing READLINK operation on a userspace NFS server. The request contain the file handle and the response include target name. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar(a)linux.vnet.ibm.com> --- fs/namei.c | 10 +++++++++- fs/open.c | 9 ++++++++- include/linux/fs.h | 1 + 3 files changed, 18 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 4d590a3..a6a8093 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1456,7 +1456,15 @@ int may_open(struct path *path, int acc_mode, int flag) switch (inode->i_mode & S_IFMT) { case S_IFLNK: - return -ELOOP; + /* + * Allow only if acc_mode contain + * open link request and read request. + */ + if (acc_mode != (MAY_OPEN_LINK | MAY_READ)) + return -ELOOP; + if (flag != O_RDONLY) + return -ELOOP; + break; case S_IFDIR: if (acc_mode & MAY_WRITE) return -EISDIR; diff --git a/fs/open.c b/fs/open.c index df5d21e..afb089e 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1268,8 +1268,15 @@ static long do_sys_open_by_handle(int mountdirfd, */ if (open_flag & __O_SYNC) open_flag |= O_DSYNC; + /* + * Handle based API allow open on a symlink + */ + if (S_ISLNK(path->dentry->d_inode->i_mode)) + acc_mode = MAY_OPEN_LINK; + else + acc_mode = MAY_OPEN; - acc_mode = MAY_OPEN | ACC_MODE(open_flag); + acc_mode |= ACC_MODE(open_flag); /* O_TRUNC implies we need access checks for write permissions */ if (open_flag & O_TRUNC) diff --git a/include/linux/fs.h b/include/linux/fs.h index a458b4e..08afa72 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -53,6 +53,7 @@ struct inodes_stat_t { #define MAY_APPEND 8 #define MAY_ACCESS 16 #define MAY_OPEN 32 +#define MAY_OPEN_LINK 64 /* * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond -- 1.7.2.rc1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |