ovl: Warn on copy up if a process has a R/O fd open to the lower file
Print a warning when overlayfs copies up a file if the process that triggered the copy up has a R/O fd open to the lower file being copied up. This can help catch applications that do things like the following: fd1 = open("foo", O_RDONLY); fd2 = open("foo", O_RDWR); where they expect fd1 and fd2 to refer to the same file - which will no longer be the case post-copy up. With this patch, the following commands: bash 5</mnt/a/foo128 6<>/mnt/a/foo128 assuming /mnt/a/foo128 to be an un-copied up file on an overlay will produce the following warning in the kernel log: overlayfs: Copying up foo129, but open R/O on fd 5 which will cease to be coherent [pid=3818 bash] This is enabled by setting: /sys/module/overlay/parameters/check_copy_up to 1. The warnings are ratelimited and are also limited to one warning per file - assuming the copy up completes in each case. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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@ -7,6 +7,7 @@
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* the Free Software Foundation.
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* the Free Software Foundation.
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*/
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*/
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/fs.h>
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#include <linux/slab.h>
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#include <linux/slab.h>
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#include <linux/file.h>
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#include <linux/file.h>
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@ -16,10 +17,41 @@
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#include <linux/uaccess.h>
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#include <linux/uaccess.h>
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#include <linux/sched.h>
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#include <linux/sched.h>
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#include <linux/namei.h>
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#include <linux/namei.h>
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#include <linux/fdtable.h>
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#include <linux/ratelimit.h>
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#include "overlayfs.h"
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#include "overlayfs.h"
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#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
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#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
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static bool __read_mostly ovl_check_copy_up;
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module_param_named(check_copy_up, ovl_check_copy_up, bool,
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S_IWUSR | S_IRUGO);
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MODULE_PARM_DESC(ovl_check_copy_up,
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"Warn on copy-up when causing process also has a R/O fd open");
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static int ovl_check_fd(const void *data, struct file *f, unsigned int fd)
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{
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const struct dentry *dentry = data;
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if (f->f_inode == d_inode(dentry))
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pr_warn_ratelimited("overlayfs: Warning: Copying up %pD, but open R/O on fd %u which will cease to be coherent [pid=%d %s]\n",
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f, fd, current->pid, current->comm);
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return 0;
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}
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/*
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* Check the fds open by this process and warn if something like the following
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* scenario is about to occur:
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*
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* fd1 = open("foo", O_RDONLY);
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* fd2 = open("foo", O_RDWR);
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*/
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static void ovl_do_check_copy_up(struct dentry *dentry)
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{
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if (ovl_check_copy_up)
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iterate_fd(current->files, 0, ovl_check_fd, dentry);
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}
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int ovl_copy_xattr(struct dentry *old, struct dentry *new)
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int ovl_copy_xattr(struct dentry *old, struct dentry *new)
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{
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{
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ssize_t list_size, size, value_size = 0;
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ssize_t list_size, size, value_size = 0;
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@ -309,6 +341,8 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
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if (WARN_ON(!workdir))
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if (WARN_ON(!workdir))
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return -EROFS;
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return -EROFS;
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ovl_do_check_copy_up(lowerpath->dentry);
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ovl_path_upper(parent, &parentpath);
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ovl_path_upper(parent, &parentpath);
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upperdir = parentpath.dentry;
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upperdir = parentpath.dentry;
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