On 10/01/2013 01:26 PM, Djalal Harouni wrote: > Since /proc entries varies at runtime, permission checks need to happen > during each system call. > > However even with that /proc file descriptors can be passed to a more > privileged process (e.g. a suid-exec) which will pass the classic > ptrace_may_access() permission check. The open() call will be issued in > general by an unprivileged process while the disclosure of sensitive > /proc information will happen using a more privileged process at > read(),write()... > > Therfore we need a more sophisticated check to detect if the cred of the > process have changed, and if the cred of the original opener that are > stored in the file->f_cred have enough permission to access the task's > /proc entries during read(), write()... > > Add the proc_allow_access() function that will receive the file->f_cred > as an argument, and tries to check if the opener had enough permission > to access the task's /proc entries. > > This function should be used with the ptrace_may_access() check. > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Suggested-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Signed-off-by: Djalal Harouni <tixxdz@xxxxxxxxxx> > --- > fs/proc/base.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > fs/proc/internal.h | 2 ++ > 2 files changed, 58 insertions(+) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index e834946..c29eeae 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -168,6 +168,62 @@ int proc_same_open_cred(const struct cred *fcred) > cap_issubset(cred->cap_permitted, fcred->cap_permitted)); > } > > +/* Returns 0 on success, -errno on denial. */ > +static int __proc_allow_access(const struct cred *cred, > + struct task_struct *task, unsigned int mode) > +{ > + int ret = 0; > + const struct cred *tcred; > + const struct cred *fcred = cred; > + > + rcu_read_lock(); > + tcred = __task_cred(task); > + if (uid_eq(fcred->uid, tcred->euid) && > + uid_eq(fcred->uid, tcred->suid) && > + uid_eq(fcred->uid, tcred->uid) && > + gid_eq(fcred->gid, tcred->egid) && > + gid_eq(fcred->gid, tcred->sgid) && > + gid_eq(fcred->gid, tcred->gid)) > + goto out; > + What's this for? Is it supposed to be an optimization? If so, it looks potentially exploitable, although I don't really understand what you're trying to do. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html