Re: retry：[PATCH] fix error: a bin file can truncate itself while running on overlayfs

[Miklos Szeredi]

Hi,

Thanks for the report and the testcase.

Here's a patch using a different approach (overlayfs philosophy is to minimize
VFS footprint).

Thanks,
Miklos
---

From: Miklos Szeredi <mszer...@redhat.com>
Subject: ovl: get_write_access() in truncate

When truncating a file we should check write access on the underlying
inode.  And we should do so on the lower file as well (before copy-up) for
consistency.

Original patch and test case by Aihua Zhang.

 - - >o >o - - test.c - - >o >o - -
#include <stdio.h>
#include <errno.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
        int ret;

        ret = truncate(argv[0], 4096);
        if (ret != -1) {
                fprintf(stderr, "truncate(argv[0]) should have failed\n");
                return 1;
        }
        if (errno != ETXTBSY) {
                perror("truncate(argv[0])");
                return 1;
        }

        return 0;
}
 - - >o >o - - >o >o - - >o >o - -

Reported-by: Aihua Zhang <zhangaih...@huawei.com>
Signed-off-by: Miklos Szeredi <mszer...@redhat.com>
Cc: <sta...@vger.kernel.org>
---
 fs/overlayfs/inode.c |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -59,16 +59,37 @@ int ovl_setattr(struct dentry *dentry, s
        if (err)
                goto out;
 
+       if (attr->ia_valid & ATTR_SIZE) {
+               struct inode *realinode = d_inode(ovl_dentry_real(dentry));
+
+               err = -ETXTBSY;
+               if (atomic_read(&realinode->i_writecount) < 0)
+                       goto out_drop_write;
+       }
+
        err = ovl_copy_up(dentry);
        if (!err) {
+               struct inode *winode = NULL;
+
                upperdentry = ovl_dentry_upper(dentry);
 
+               if (attr->ia_valid & ATTR_SIZE) {
+                       winode = d_inode(upperdentry);
+                       err = get_write_access(winode);
+                       if (err)
+                               goto out_drop_write;
+               }
+
                inode_lock(upperdentry->d_inode);
                err = notify_change(upperdentry, attr, NULL);
                if (!err)
                        ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
                inode_unlock(upperdentry->d_inode);
+
+               if (winode)
+                       put_write_access(winode);
        }
+out_drop_write:
        ovl_drop_write(dentry);
 out:
        return err;