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Subject[100/107] deal with races in /proc/*/{syscall,stack,personality}
2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Al Viro <viro@zeniv.linux.org.uk>

commit a9712bc12c40c172e393f85a9b2ba8db4bf59509 upstream.

All of those are rw-r--r-- and all are broken for suid - if you open
a file before the target does suid-root exec, you'll be still able
to access it. For personality it's not a big deal, but for syscall
and stack it's a real problem.

Fix: check that task is tracable for you at the time of read().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/proc/base.c | 69 +++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 50 insertions(+), 19 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -328,6 +328,23 @@ static int proc_pid_wchan(struct task_st
}
#endif /* CONFIG_KALLSYMS */

+static int lock_trace(struct task_struct *task)
+{
+ int err = mutex_lock_killable(&task->cred_guard_mutex);
+ if (err)
+ return err;
+ if (!ptrace_may_access(task, PTRACE_MODE_ATTACH)) {
+ mutex_unlock(&task->cred_guard_mutex);
+ return -EPERM;
+ }
+ return 0;
+}
+
+static void unlock_trace(struct task_struct *task)
+{
+ mutex_unlock(&task->cred_guard_mutex);
+}
+
#ifdef CONFIG_STACKTRACE

#define MAX_STACK_TRACE_DEPTH 64
@@ -337,6 +354,7 @@ static int proc_pid_stack(struct seq_fil
{
struct stack_trace trace;
unsigned long *entries;
+ int err;
int i;

entries = kmalloc(MAX_STACK_TRACE_DEPTH * sizeof(*entries), GFP_KERNEL);
@@ -347,15 +365,20 @@ static int proc_pid_stack(struct seq_fil
trace.max_entries = MAX_STACK_TRACE_DEPTH;
trace.entries = entries;
trace.skip = 0;
- save_stack_trace_tsk(task, &trace);

- for (i = 0; i < trace.nr_entries; i++) {
- seq_printf(m, "[<%p>] %pS\n",
- (void *)entries[i], (void *)entries[i]);
+ err = lock_trace(task);
+ if (!err) {
+ save_stack_trace_tsk(task, &trace);
+
+ for (i = 0; i < trace.nr_entries; i++) {
+ seq_printf(m, "[<%p>] %pS\n",
+ (void *)entries[i], (void *)entries[i]);
+ }
+ unlock_trace(task);
}
kfree(entries);

- return 0;
+ return err;
}
#endif

@@ -527,18 +550,22 @@ static int proc_pid_syscall(struct task_
{
long nr;
unsigned long args[6], sp, pc;
+ int res = lock_trace(task);
+ if (res)
+ return res;

if (task_current_syscall(task, &nr, args, 6, &sp, &pc))
- return sprintf(buffer, "running\n");
-
- if (nr < 0)
- return sprintf(buffer, "%ld 0x%lx 0x%lx\n", nr, sp, pc);
-
- return sprintf(buffer,
+ res = sprintf(buffer, "running\n");
+ else if (nr < 0)
+ res = sprintf(buffer, "%ld 0x%lx 0x%lx\n", nr, sp, pc);
+ else
+ res = sprintf(buffer,
"%ld 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx\n",
nr,
args[0], args[1], args[2], args[3], args[4], args[5],
sp, pc);
+ unlock_trace(task);
+ return res;
}
#endif /* CONFIG_HAVE_ARCH_TRACEHOOK */

@@ -2497,8 +2524,12 @@ static int proc_tgid_io_accounting(struc
static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task)
{
- seq_printf(m, "%08x\n", task->personality);
- return 0;
+ int err = lock_trace(task);
+ if (!err) {
+ seq_printf(m, "%08x\n", task->personality);
+ unlock_trace(task);
+ }
+ return err;
}

/*
@@ -2517,13 +2548,13 @@ static const struct pid_entry tgid_base_
REG("environ", S_IRUSR, proc_environ_operations),
INF("auxv", S_IRUSR, proc_pid_auxv),
ONE("status", S_IRUGO, proc_pid_status),
- ONE("personality", S_IRUSR, proc_pid_personality),
+ ONE("personality", S_IRUGO, proc_pid_personality),
INF("limits", S_IRUSR, proc_pid_limits),
#ifdef CONFIG_SCHED_DEBUG
REG("sched", S_IRUGO|S_IWUSR, proc_pid_sched_operations),
#endif
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
- INF("syscall", S_IRUSR, proc_pid_syscall),
+ INF("syscall", S_IRUGO, proc_pid_syscall),
#endif
INF("cmdline", S_IRUGO, proc_pid_cmdline),
ONE("stat", S_IRUGO, proc_tgid_stat),
@@ -2551,7 +2582,7 @@ static const struct pid_entry tgid_base_
INF("wchan", S_IRUGO, proc_pid_wchan),
#endif
#ifdef CONFIG_STACKTRACE
- ONE("stack", S_IRUSR, proc_pid_stack),
+ ONE("stack", S_IRUGO, proc_pid_stack),
#endif
#ifdef CONFIG_SCHEDSTATS
INF("schedstat", S_IRUGO, proc_pid_schedstat),
@@ -2856,13 +2887,13 @@ static const struct pid_entry tid_base_s
REG("environ", S_IRUSR, proc_environ_operations),
INF("auxv", S_IRUSR, proc_pid_auxv),
ONE("status", S_IRUGO, proc_pid_status),
- ONE("personality", S_IRUSR, proc_pid_personality),
+ ONE("personality", S_IRUGO, proc_pid_personality),
INF("limits", S_IRUSR, proc_pid_limits),
#ifdef CONFIG_SCHED_DEBUG
REG("sched", S_IRUGO|S_IWUSR, proc_pid_sched_operations),
#endif
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
- INF("syscall", S_IRUSR, proc_pid_syscall),
+ INF("syscall", S_IRUGO, proc_pid_syscall),
#endif
INF("cmdline", S_IRUGO, proc_pid_cmdline),
ONE("stat", S_IRUGO, proc_tid_stat),
@@ -2889,7 +2920,7 @@ static const struct pid_entry tid_base_s
INF("wchan", S_IRUGO, proc_pid_wchan),
#endif
#ifdef CONFIG_STACKTRACE
- ONE("stack", S_IRUSR, proc_pid_stack),
+ ONE("stack", S_IRUGO, proc_pid_stack),
#endif
#ifdef CONFIG_SCHEDSTATS
INF("schedstat", S_IRUGO, proc_pid_schedstat),



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