2011/3/8 Andreas Dilger <adilger.kernel@xxxxxxxxx>: > On 2011-03-07, at 10:11 PM, Dave Chinner wrote: >> On Sat, Mar 05, 2011 at 10:37:45AM +0100, Marco Stornelli wrote: >>> From: Marco Stornelli <marco.stornelli@xxxxxxxxx> >>> >>> In the fallocate path the kernel doesn't check for the immutable/append >>> flag. It's possible to have a race condition in this scenario: an >>> application open a file in read/write and it does something, meanwhile >>> root set the immutable flag on the file, the application at that point >>> can call fallocate with success. In addition, we don't allow to do any >>> unreserve operation on an append only file but only the reserve one. >>> >>> Signed-off-by: Marco Stornelli <marco.stornelli@xxxxxxxxx> >>> --- >>> Patch is against 2.6.38-rc7 >>> >>> ChangeLog: >>> v3: Modified do_fallocate instead of every single fs >>> v2: Added the check for append-only file for XFS >>> v1: First draft >>> >>> --- open.c.orig 2011-03-01 22:55:12.000000000 +0100 >>> +++ open.c 2011-03-04 15:28:43.000000000 +0100 >>> @@ -233,6 +233,14 @@ int do_fallocate(struct file *file, int >>> >>> if (!(file->f_mode & FMODE_WRITE)) >>> return -EBADF; >>> + >>> + /* It's not possible punch hole on append only file */ >>> + if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode)) >>> + return -EPERM; >> >> Seeing as I didn't get an answer in before you reposted, I still >> think punching an append-only file is a valid thing to want to do. >> >> I've seen this done in the past for application-level transaction >> journal files. The journal file is append only so new transactions >> can only be written at the end of the file i.e. you cannot overwrite >> (and therefore corrupt) existing transactions. However, once a >> transaction is complete and the changes flushed to disk, the >> transaction is punched out of the file to zero the range so it >> doesn't get replayed during recovery after a system crash. > > To my thinking "append only" means just that - only new data can be written at the end of the file, and existing data cannot be >modified. Allowing hole punch on such a file (e.g. range 0 .. ~0) would allow erasing all of the data, entirely bypassing the >append-only flag. > > Cheers, Andreas > I quite agree with Andreas. Marco -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
