Commit a3fbbde7 authored by Al Viro's avatar Al Viro Committed by Linus Torvalds
Browse files

VFS: we need to set LOOKUP_JUMPED on mountpoint crossing



Mountpoint crossing is similar to following procfs symlinks - we do
not get ->d_revalidate() called for dentry we have arrived at, with
unpleasant consequences for NFS4.

Simple way to reproduce the problem in mainline:

    cat >/tmp/a.c <<'EOF'
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdio.h>
    main()
    {
            struct flock fl = {.l_type = F_RDLCK, .l_whence = SEEK_SET, .l_len = 1};
            if (fcntl(0, F_SETLK, &fl))
                    perror("setlk");
    }
    EOF
    cc /tmp/a.c -o /tmp/test

then on nfs4:

    mount --bind file1 file2
    /tmp/test < file1		# ok
    /tmp/test < file2		# spews "setlk: No locks available"...

What happens is the missing call of ->d_revalidate() after mountpoint
crossing and that's where NFS4 would issue OPEN request to server.

The fix is simple - treat mountpoint crossing the same way we deal with
following procfs-style symlinks.  I.e.  set LOOKUP_JUMPED...

Cc: stable@kernel.org
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 54a0f913
......@@ -852,7 +852,7 @@ static int follow_managed(struct path *path, unsigned flags)
mntput(path->mnt);
if (ret == -EISDIR)
ret = 0;
return ret;
return ret < 0 ? ret : need_mntput;
}
int follow_down_one(struct path *path)
......@@ -900,6 +900,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
break;
path->mnt = mounted;
path->dentry = mounted->mnt_root;
nd->flags |= LOOKUP_JUMPED;
nd->seq = read_seqcount_begin(&path->dentry->d_seq);
/*
* Update the inode too. We don't need to re-check the
......@@ -1213,6 +1214,8 @@ retry:
path_put_conditional(path, nd);
return err;
}
if (err)
nd->flags |= LOOKUP_JUMPED;
*inode = path->dentry->d_inode;
return 0;
}
......@@ -2146,6 +2149,10 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
}
/* create side of things */
/*
* This will *only* deal with leaving RCU mode - LOOKUP_JUMPED has been
* cleared when we got to the last component we are about to look up
*/
error = complete_walk(nd);
if (error)
return ERR_PTR(error);
......@@ -2214,6 +2221,9 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
if (error < 0)
goto exit_dput;
if (error)
nd->flags |= LOOKUP_JUMPED;
error = -ENOENT;
if (!path->dentry->d_inode)
goto exit_dput;
......@@ -2223,6 +2233,10 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
path_to_nameidata(path, nd);
nd->inode = path->dentry->d_inode;
/* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */
error = complete_walk(nd);
if (error)
goto exit;
error = -EISDIR;
if (S_ISDIR(nd->inode->i_mode))
goto exit;
......
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