Commit 0640113b authored by Linus Torvalds's avatar Linus Torvalds

vfs: Fix /proc/<tid>/fdinfo/<fd> file handling

Cyrill Gorcunov reports that I broke the fdinfo files with commit
30a08bf2 ("proc: move fd symlink i_mode calculations into
tid_fd_revalidate()"), and he's quite right.

The tid_fd_revalidate() function is not just used for the <tid>/fd
symlinks, it's also used for the <tid>/fdinfo/<fd> files, and the
permission model for those are different.

So do the dynamic symlink permission handling just for symlinks, making
the fdinfo files once more appear as the proper regular files they are.

Of course, Al Viro argued (probably correctly) that we shouldn't do the
symlink permission games at all, and make the symlinks always just be
the normal 'lrwxrwxrwx'.  That would have avoided this issue too, but
since somebody noticed that the permissions had changed (which was the
reason for that original commit 30a08bf2 in the first place), people
do apparently use this feature.

[ Basically, you can use the symlink permission data as a cheap "fdinfo"
  replacement, since you see whether the file is open for reading and/or
  writing by just looking at st_mode of the symlink.  So the feature
  does make sense, even if the pain it has caused means we probably
  shouldn't have done it to begin with. ]
Reported-and-tested-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5041caa4
...@@ -1803,7 +1803,7 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd) ...@@ -1803,7 +1803,7 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
rcu_read_lock(); rcu_read_lock();
file = fcheck_files(files, fd); file = fcheck_files(files, fd);
if (file) { if (file) {
unsigned i_mode, f_mode = file->f_mode; unsigned f_mode = file->f_mode;
rcu_read_unlock(); rcu_read_unlock();
put_files_struct(files); put_files_struct(files);
...@@ -1819,12 +1819,14 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd) ...@@ -1819,12 +1819,14 @@ static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
inode->i_gid = GLOBAL_ROOT_GID; inode->i_gid = GLOBAL_ROOT_GID;
} }
i_mode = S_IFLNK; if (S_ISLNK(inode->i_mode)) {
unsigned i_mode = S_IFLNK;
if (f_mode & FMODE_READ) if (f_mode & FMODE_READ)
i_mode |= S_IRUSR | S_IXUSR; i_mode |= S_IRUSR | S_IXUSR;
if (f_mode & FMODE_WRITE) if (f_mode & FMODE_WRITE)
i_mode |= S_IWUSR | S_IXUSR; i_mode |= S_IWUSR | S_IXUSR;
inode->i_mode = i_mode; inode->i_mode = i_mode;
}
security_task_to_inode(task, inode); security_task_to_inode(task, inode);
put_task_struct(task); put_task_struct(task);
...@@ -1859,6 +1861,7 @@ static struct dentry *proc_fd_instantiate(struct inode *dir, ...@@ -1859,6 +1861,7 @@ static struct dentry *proc_fd_instantiate(struct inode *dir,
ei = PROC_I(inode); ei = PROC_I(inode);
ei->fd = fd; ei->fd = fd;
inode->i_mode = S_IFLNK;
inode->i_op = &proc_pid_link_inode_operations; inode->i_op = &proc_pid_link_inode_operations;
inode->i_size = 64; inode->i_size = 64;
ei->op.proc_get_link = proc_fd_link; ei->op.proc_get_link = proc_fd_link;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment