Messages in this thread | | | Date | Tue, 22 Apr 2003 13:54:09 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: kernel ring buffer accessible by users |
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On Tue, 22 Apr 2003, Julien Oster wrote:
> On Tue, Apr 22, 2003 at 06:44:05PM +0200, Michael Buesch wrote: > > Hello Michael, > > > > it's been quite a while that I noticed that any ordinary user, not > > > just root, can type "dmesg" to see the kernel ring buffer. > > > just make > > $ chmod 700 /bin/dmesg > > Thanks for the answer, but that doesn't help that much, since any user > could copy dmesg from his system or simply code a dmesg replacement > within a few minutes. > > Regards, > Julien > -
dmesg gets it's data from syslog(0x03, char *buf, size_t buf_len) where 0x03 says 'read' up to 4k.
The kernel interface is documented to return -EPERM if the effective user isn't root. I have just tried `dmesg` from several machines with various versions of Linux and they all allow a user to read.
The usual "tie-breaker" I use for configuration problems is my Sun. It runs SunOs 5.5.1 and it allows an ordinary user to execute `dmesg` and read kernel messages.
Script started on Tue Apr 22 13:49:44 2003 $ rlogin -l johnson hal Password: Last login: Wed Nov 6 09:29:53 from chaos hal:/export/home/johnson[1] who am i johnson pts/0 Apr 22 13:42 (chaos) hal:/export/home/johnson[2] dmesg
Apr 22 13:42 SunOS Release 5.5.1 Version Generic [UNIX(R) System V Release 4.0] Copyright (c) 1983-1996, Sun Microsystems, Inc. vac: enabled in writeback mode cpu0: FMI,MB86907 (mid 0 impl 0x0 ver 0x5 clock 170 MHz) mem = 32768K (0x2000000) avail mem = 28446720 Ethernet address = 8:0:20:8e:b:0 root nexus = SUNW,SPARCstation-5 iommu0 at root: obio 0x10000000 sbus0 at iommu0: obio 0x10001000 espdma0 at sbus0: SBus slot 5 0x8400000 esp0 at espdma0: SBus slot 5 0x8800000 sparc ipl 4 sd0 at esp0: target 0 lun 0 sd0 is /iommu@0,10000000/sbus@0,10001000/espdma@5,8400000/esp@5,8800000/sd@0,0 <SEAGATE-ST32155N-0532 cyl 4162 alt 2 hd 8 sec 126> sd2 at esp0: target 2 lun 0 sd2 is /iommu@0,10000000/sbus@0,10001000/espdma@5,8400000/esp@5,8800000/sd@2,0 Vendor 'PIONEER', product 'DE-C7001', (unknown capacity) sd3 at esp0: target 3 lun 0 sd3 is /iommu@0,10000000/sbus@0,10001000/espdma@5,8400000/esp@5,8800000/sd@3,0 <SUN2.1G cyl 2733 alt 2 hd 19 sec 80> root on /iommu@0,10000000/sbus@0,10001000/espdma@5,8400000/esp@5,8800000/sd@3,0:a fstype ufs obio0 at root zs0 at obio0: obio 0x100000 sparc ipl 12 zs0 is /obio/zs@0,100000 zs1 at obio0: obio 0x0 sparc ipl 12 zs1 is /obio/zs@0,0 cgsix0 at sbus0: SBus slot 3 0x0 SBus level 5 sparc ipl 9 cgsix0 is /iommu@0,10000000/sbus@0,10001000/cgsix@3,0 cgsix0: screen 1152x900, single buffered, 1M mappable, rev 11 cpu 0 initialization complete - online ledma0 at sbus0: SBus slot 5 0x8400010 le0 at ledma0: SBus slot 5 0x8c00000 sparc ipl 6 le0 is /iommu@0,10000000/sbus@0,10001000/ledma@5,8400010/le@5,8c00000 dump on /dev/dsk/c0t3d0s1 size 66108K pcmcia: no PCMCIA adapters found hal:/export/home/johnson[3] exit logout rlogin: connection closed. # exit exit Script done on Tue Apr 22 13:50:18 2003
It doesn't look like there's anything that an ordinary user shouldn't see. If somebody has written code that sends proprietary information out this "hole", that code should be fixed, not this.
Cheers, Dick Johnson Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips). Why is the government concerned about the lunatic fringe? Think about it.
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