Shaya Potter wrote:
unionfs_permission does this
err = permission(hidden_inode, mask, nd);
/* If the leftmost branch is r/o we can't copyup.
* Otherwise we ignore EROFS. */
if (IS_COPYUP_ERR(err) && (bindex != 0))
err = inode_permission(hidden_inode, mask, nd);
since inode_permission seems to bascially be the samething as
permission, what exactly is the point of this? as nothing changes b/w
the calls?
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Hello,
The issue that we ran into was that permission will return right
away if we are trying to request write permissions on a read only file
system. This was causing a bug where we wouldn't check the permissions
on a file if it existed on a read only file system.so what would happen
is that the file would be copied up regardless of whether the person has
the proper permissions for the file and in the case of something like
passwd or another file this would allow you to chmod or chown a file to
any user/permissions you wanted and then you could edit it as much as
you want. So what we did here is we copied the permission function but
removed the failure on erofs. This way even if its on a read only file
system we can check the actual permissions of the file to see if we
would be allowed to write to it if it weren't on a read only file system
and if we can we would then copy it up and allow the person to write to
it. Otherwise it should fail with EACCESS.
Dave
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