> On Dec 4, 2015, at 4:11 PM, Theodore Ts'o <tytso@xxxxxxx> wrote: > > On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote: >> On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote: >>> Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611 >>> a little while ago :) The same question was asked 16 years ago. Apparently >>> the answer then was that it was easier than fixing the code. >> >> So it seems then that either it still isn't safe and so unprivileged >> users shouldn't be allowed to do it at all, or else it's safe and we >> should drop the requirement completely. I can't say which is right, >> unfortunately. > > It may not have been safe 16 years agoo, but giving invalid arguments > to FIBMAP is safe for ext4 and ext2. This is the sort of thing that > tools like trinity should and does test for, so I think it should be > fine to remove the root check for FIBMAP. You can use FIEMAP on regular files and directories without special permission: $ filefrag -v /etc Filesystem type is: ef53 File size of /etc is 12288 (3 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 0: 8396832.. 8396832: 1: 1: 1.. 2: 8397051.. 8397052: 2: 8396833: last,eof /etc: 2 extents found FIEMAP also has the benefit that you don't need to call it millions of times for large files, like is needed for FIBMAP. Cheers, Andreas
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