linux-kernel - Re: rpc.mountd crashes when extensively using netgroups

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Message-ID: <alpine.LFD.0.999.0708030801090.23798@enigma.security.iitk.ac.in>
Date:	Fri, 3 Aug 2007 08:10:35 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Stefan Walter <stefan.walter@....ethz.ch>
cc:	Steve Dickson <SteveD@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: rpc.mountd crashes when extensively using netgroups

Hi,


On Thu, 2 Aug 2007, Stefan Walter wrote:

> Steve Dickson wrote:
> > Stefan Walter wrote:
> >>
> >> We do this on a much larger scale though. The bug we ran into is
> >> in line 96 in utils/mountd/auth.c. The strcpy can corrupt
> >> memory when it copies the string returned by client_compose() to
> >> my_client.m_hostname which has a fixed size of 1024 bytes. For our
> >> example above, client_compose() returns "@joe,@jane"
> >> for any machine in the offices_1 netgroup. Unfortunately we have
> >> a machine to which roughly 150 netgroups like @joe or @jane
>> export to and client_compose() returns a string over 1300 bytes
> >> long and rpc.mountd nicely segfaults.
> >>  
> >> To prevent the crash is of course trivial: Inserting a simple
> >> 'if (strlen(n) > 1024) return NULL;' before line 96 does the job.
> > Does the attached patch help?
> >
> rpc.mountd does not crash anymore but I get a 'permission denied' when
> trying
> to mount a share. Doing an 'strace rpc.mountd -F' reveals:
> 
> ...
> open("/proc/net/rpc/auth.unix.ip/channel", O_WRONLY|O_CREAT|O_TRUNC,
> 0666) = 9
> fstat64(9, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f41000
> time(NULL)                              = 1186041882
> write(9, "nfsd 129.132.10.33 1186043682 @a"..., 1024) = -1 EINVAL
> (Invalid argument)
> write(9, "\n", 1)                       = -1 EINVAL (Invalid argument)
> close(9)                                = 0
> munmap(0xb7f41000, 4096)                = 0
> open("/proc/net/rpc/nfsd.export/channel", O_WRONLY|O_CREAT|O_TRUNC,
> 0666) = 9
> fstat64(9, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f41000
> write(9, "@anbuehle,@anhorni,@antoinet,@ap"..., 1024) = -1 EINVAL
> (Invalid argument)
> time(NULL)                              = 1186041882
> write(9, "/export/groups/grossm/h1/home/gr"..., 68) = -1 ENOENT (No such
> file or directory)
> close(9)                                = 0
> munmap(0xb7f41000, 4096)                = 0
> open("/proc/fs/nfsd/filehandle", O_RDWR) = 9
> fstat64(9, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
> mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0xb7f41000
> write(9, "@anbuehle,@anhorni,@antoinet,@ap"..., 1066) = -1 EPERM
> (Operation not permitted)
> ...

Yup, the snprintf() in the patch would've truncated the input string.

Steve (D), you should check the return of snprintf() and compare against
the size specified (NFSCLNT_IDMAX+1) and do a graceful cleanup + print
an error message to the user, when detecting truncation of input:


err = snprintf(my_client.m_hostname, (NFSCLNT_IDMAX+1), "%s", *n?n:"DEFAULT");
if (err >= (NFSCLNT_IDMAX+1)) {
	printf("too large input string ...\n");
	/* cleanups and graceful exit */
}


Sorry, I don't have rpc.mountd sources nearby, so cannot make a patch
myself (I'm an exclusively kernel guy :-)


Thanks,
Satyam
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