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I'm not sure why mount is installed with SUID bit on many distributions.
In graphical environment, it doesn't require user to type the mount command to mount a partition. Normally udisks will communicate with another daemon to mount the drive.
And on a server, I don't see the necessity as well.
So, is there any reason to have SUID bit set?
mount() requires root (or CAP_SYS_ADMIN on Linux), but it is possible to specify a mountpoint in /etc/fstab that is allowed to be mounted by a user by using the users option. To facilitate this, they need to elevate to the superuser account to be able to execute mount() successfully.
It will depend on the options used when the drives are mounted.
Have a look at /etc/fstab, if the entry for the partitions in question has defaults set as an option then this implies that suid is set, from man mount[1]...
defaults
Use default options: rw, suid, dev, exec, auto, nouser, and async.
You can over-ride this by specifying alternative options in /etc/fstab, for example you can specify users as an option (although I was caught out by the fact that this implies noexec so I couldn't run any scripts and had to over-ride this), so have this in my /etc/fstab:
LABEL=home /home ext4 noatime,users,exec 0 4
[1] I was reading man mount and man fstab yesterday after having a problem with default options myself.
users in /etc/fstab but also highlights something which bit me yesterday which was the default options that users implies prevent execution and can over-ridden with exec). Happy for it to be deleted though.
– slackline
Jan 2 '14 at 11:17
