"Serge E. Hallyn" <serue@xxxxxxxxxx> writes: > Quoting H. Peter Anvin (hpa@xxxxxxxxx): >> Miklos Szeredi wrote: >> > >> > Andrew, please skip this patch, for now. >> > >> > Serge found a problem with the fsuid approach: setfsuid(nonzero) will >> > remove filesystem related capabilities. So even if root is trying to >> > set the "user=UID" flag on a mount, access to the target (and in case >> > of bind, the source) is checked with user privileges. >> > >> > Root should be able to set this flag on any mountpoint, _regardless_ >> > of permissions. >> > >> >> Right, if you're using fsuid != 0, you're not running as root > > Sure, but what I'm not clear on is why, if I've done a > prctl(PR_SET_KEEPCAPS, 1) before the setfsuid, I still lose the > CAP_FS_MASK perms. I see the special case handling in > cap_task_post_setuid(). I'm sure there was a reason for it, but > this is a piece of the capability implementation I don't understand > right now. So we drop CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, and CAP_FSETID Since we are checking CAP_SETUID or CAP_SYS_ADMIN how is that a problem? Are there other permission checks that mount is doing that we care about. >> (fsuid is >> the equivalent to euid for the filesystem.) > > If it were really the equivalent then I could keep my capabilities :) > after changing it. We drop all capabilities after we change the euid. >> I fail to see how ruid should have *any* impact on mount(2). That seems >> to be a design flaw. > > May be, but just using fsuid at this point stops me from enabling user > mounts under /share if /share is chmod 000 (which it is). I'm dense today. If we can't work out the details we can always use a flag. But what is the problem with fsuid? You are not trying to test this using a non-default security model are you? Eric - 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
