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?
There are however two issues for which we could not find an easy
solution:
1. For every client rpc.mountd and the kernel seem to exchange
and use lists with _all_ netgroups used in exports that are
relevant for granting permission to some share for a particular
client. We could imagine two optimizations here:
* Resolve netgroups and only put the (member) netgroups that
contained the host name that would be used to authorize
a mount in the list.
* Use the list of mounted paths per client and only put the
netgroup(s) used to export paths that are actually mounted
on a client.
These sound reasonable...
2. Using a fixed size for NFSCLNT_IDMAX does not scale. Mounting
shares on a client for which the 'if' clause of the quick fix
becomes true will not be possible. We thought about enlarging
NFSCLNT_IDMAX and using a custom kernel but dropped the idea.
True...
Our ultimate goal is to get Red Hat fix the code in nfs-utils 1.0.6
that is used in RHEL4. A first step would be to get a suitable fix in
the current nfs-utils.
Please open up bugs on all three of these issues and
we'll see what can done...
steved.
commit 851ce1cb766cf295db85900aab804c0f82c12ab3
Author: Steve Dickson <[email protected]>
Date: Tue Jul 31 09:57:19 2007 -0400
Stop rpc.mound from crashing by m_hostname becoming
corrupted with very long host names.
Signed-off-by: Steve Dickson <[email protected]>
diff --git a/utils/mountd/auth.c b/utils/mountd/auth.c
index f7fe23d..eff0ba7 100644
--- a/utils/mountd/auth.c
+++ b/utils/mountd/auth.c
@@ -93,7 +93,8 @@ auth_authenticate_internal(char *what, struct sockaddr_in *caller,
*error = unknown_host;
if (!n)
return NULL;
- strcpy(my_client.m_hostname, *n?n:"DEFAULT");
+ snprintf(my_client.m_hostname, (NFSCLNT_IDMAX+1),
+ "%s", *n?n:"DEFAULT");
free(n);
my_client.m_naddr = 1;
my_exp.m_client = &my_client;
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