Memory leak caused by forwarded GSSAPI credential store

[miguel.sanders at arcelormittal.com]

Hi guys

While debugging a GSSAPI memory allocation problem not related to OpenSSH, I found a memory leak in OpenSSH when storing  forwarded GSSAPI credentials resulting in a growing process segment for each connection that uses GSSAPI credentials  forwarding. What happens is the following:
In the privileged parent, we are calling ssh_gssapi_storecreds() which itself calls ssh_gssapi_krb5_storecreds().  ssh_gssapi_krb5_storecreds() makes some memory allocations in order to save the credentials store for the gssapi client.

  +167          client->store.filename = xstrdup(krb5_cc_get_name(krb_context, ccache));
  +168          client->store.envvar = "KRB5CCNAME";
  +169          len = strlen(client->store.filename) + 6;
  +170          client->store.envval = xmalloc(len);
  +171          snprintf(client->store.envval, len, "FILE:%s", client->store.filename);

Those memory allocations are never freed. Moreover, since those memory allocations are done in the privileged parent (which  is a finite-state machine and never returns) before forking the unprivileged child, the memory leak gets doubled for each  connection that uses GSSAPI credential forwarding.

A solution would be the following:
1) Migrate the ssh_gssapi_storecreds() call to the unprivileged child
2) Create a ssh_gssapi_free_store() call in gss-serv.c which frees the memory allocations. At first I was thinking of  integrating this in the ssh_gssapi_cleanup_creds() call but freeing the memory is mandatory while the cleanup of credentials  is the user's choice.
3) Integrate ssh_gssapi_free_store() call in the do_cleanup() call, which is located in session.c.

Bugzilla item #1601 was created to address this issue.
I also added a patch which solves this issue.

Met vriendelijke groet
Best regards
Bien à vous

Miguel SANDERS
ArcelorMittal Gent

UNIX Systems & Storage
IT Supply Western Europe | John Kennedylaan 51
B-9042 Gent

T +32 9 347 3538 | F +32 9 347 4901 | M +32478 805 023
E miguel.sanders at arcelormittal.com
www.arcelormittal.com/gent


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