On Sun, 2011-12-11 at 17:51 +0100, Sven Vermeulen wrote: > Hi all, > > I'm trying to debug a (less important) case of SSHd segfaulting when the > user is running in permissive mode but has a wrongly labeled system, > resulting in the sshd binary running in the kernel_t context. It looks like > this causes a double-free (or something similar) [1] in the code and I'm > trying to figure out how to best deal with this. > > [1] https://bugs.gentoo.org/show_bug.cgi?id=377203 > > >From the looks of it, I think it boils down to get_default_context which > returns -1 (as expected) but either leaves the security_context_t as-is or > makes it NULL. > > 98 int get_default_context(const char *user, > 99 security_context_t fromcon, security_context_t * newcon) > 100 { > 101 security_context_t *conary; > 102 int rc; > 103 > 104 rc = get_ordered_context_list(user, fromcon, &conary); > 105 if (rc <= 0) > 106 return -1; > 107 > 108 *newcon = strdup(conary[0]); > 109 freeconary(conary); > 110 if (!(*newcon)) > 111 return -1; > 112 return 0; > 113 } > > Am I correct to state that, if the newcon variable was not set to a valid > security_context_t before, then I can just set newcon to NULL? > > Like in OpenSSH's ssh_selinux_getctxbyname: > > static security_context_t ssh_selinux_getctxbyname(char *pwname) { > security_context_t sc; > ... > r = get_default_context(pwname, NULL, &sc); > > return(sc); > } > > I think the above might be updated with: > > if (r != -1) > return(sc); > else > return(NULL); > > Otherwise a later call tries to freecon(sc) which then fails (in case of > OpenSSH, that's in ssh_selinux_setup_exec_context()). > > Am I making sense here? That would work, or you could initialize sc to NULL before calling get_default_context(), and then unconditionally return sc. -- Stephen Smalley National Security Agency -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
