On Fri, 2009-08-07 at 16:38 -0400, Eric Paris wrote: > On Sat, 2009-08-08 at 05:23 +0900, OGAWA Hirofumi wrote: > > Eric Paris <eparis@xxxxxxxxxx> writes: > > > > > On Fri, 2009-08-07 at 06:05 -0400, Amerigo Wang wrote: > > >> V2 -> V3: > > >> Call notify_change() before clearing suid/sgid. > > >> Thanks to OGAWA Hirofumi. > > >> > > >> V1 -> V2: > > >> Introduce dentry_remove_suid(), and use it in do_truncate(). > > >> Thanks to Eric Paris. > > >> > > >> > > >> When suid is set and the non-owner user has write permission, > > >> any writing into this file should be allowed and suid should be > > >> removed after that. > > >> > > >> However, current kernel only allows writing without truncations, > > >> when we do truncations on that file, we get EPERM. This is a bug. > > >> > > >> Steps to reproduce this bug: > > >> > > >> % ls -l rootdir/file1 > > >> -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 > > >> % echo h > rootdir/file1 > > >> zsh: operation not permitted: rootdir/file1 > > >> % ls -l rootdir/file1 > > >> -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 > > >> % echo h >> rootdir/file1 > > >> % ls -l rootdir/file1 > > >> -rwxrwxrwx 1 root root 5 Jun 25 16:34 rootdir/file1 > > >> > > >> This patch fixes it. > > >> > > >> Signed-off-by: WANG Cong <amwang@xxxxxxxxxx> > > >> Cc: Eric Sandeen <esandeen@xxxxxxxxxx> > > >> Cc: Eric Paris <eparis@xxxxxxxxxx> > > >> Cc: Eugene Teo <eteo@xxxxxxxxxx> > > >> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > > >> Cc: hirofumi@xxxxxxxxxxxxxxxxxx > > > > > > I was thinking about this and kept telling myself I was going to test v2 > > > before I ack/nak. Clearly we shouldn't for the dropping of SUID if the > > > process didn't have permission to change the ATTR_SIZE. > > > > > > Acked-by: Eric Paris <eparis@xxxxxxxxxx> > > > > BTW, Do you know why doesn't security modules fix the handling of > > do_truncate() (i.e. ATTR_MODE | ATTR_SIZE). And why doesn't it allow to > > pass ATTR_FORCE for it? > > I'm not sure what you mean. I understood ATTR_FORCE to mean 'I am magic > and get to override all security checks." Which is why nothing should > ever be using ATTR_FORCE with things other than SUID. > > I guess we could somehow force logic into the LSM to make it only apply > to SUID and friends but I'm not sure it buys us anything. SELinux shouldn't apply a permission check for the clearing of the suid bit on write or truncate. It should only apply a permission check for the actual truncate or write operation, and then the clearing of the suid bit should always be forced if that check passed. -- Stephen Smalley National Security Agency -- 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
