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proc: avoid information leaks to non-privileged processes

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By using the same test as is used for /proc/pid/maps and /proc/pid/smaps,
only allow processes that can ptrace() a given process to see information
that might be used to bypass address space layout randomization (ASLR).
These include eip, esp, wchan, and start_stack in /proc/pid/stat as well
as the non-symbolic output from /proc/pid/wchan.

ASLR can be bypassed by sampling eip as shown by the proof-of-concept
code at http://code.google.com/p/fuzzyaslr/ As part of a presentation
(http://www.cr0.org/paper/to-jt-linux-alsr-leak.pdf) esp and wchan were
also noted as possibly usable information leaks as well.  The
start_stack address also leaks potentially useful information.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Jake Edge <jake@lwn.net>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jake Edge 2009-05-04 12:51:14 -06:00 committed by Linus Torvalds
parent 7fdf523067
commit f83ce3e6b0
2 changed files with 13 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
fs/proc/array.c
View file

@ -80,6 +80,7 @@
#include <linux/delayacct.h>
#include <linux/seq_file.h>
#include <linux/pid_namespace.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
#include <asm/pgtable.h>
@ -352,6 +353,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
char state;
pid_t ppid = 0, pgid = -1, sid = -1;
int num_threads = 0;
int permitted;
struct mm_struct *mm;
unsigned long long start_time;
unsigned long cmin_flt = 0, cmaj_flt = 0;
@ -364,11 +366,14 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
state = *get_task_state(task);
vsize = eip = esp = 0;
permitted = ptrace_may_access(task, PTRACE_MODE_READ);
mm = get_task_mm(task);
if (mm) {
vsize = task_vsize(mm);
eip = KSTK_EIP(task);
esp = KSTK_ESP(task);
if (permitted) {
eip = KSTK_EIP(task);
esp = KSTK_ESP(task);
}
}
get_task_comm(tcomm, task);
@ -424,7 +429,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
unlock_task_sighand(task, &flags);
}
if (!whole || num_threads < 2)
if (permitted && (!whole || num_threads < 2))
wchan = get_wchan(task);
if (!whole) {
min_flt = task->min_flt;
@ -476,7 +481,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
rsslim,
mm ? mm->start_code : 0,
mm ? mm->end_code : 0,
mm ? mm->start_stack : 0,
(permitted && mm) ? mm->start_stack : 0,
esp,
eip,
/* The signal information here is obsolete.

5
fs/proc/base.c
View file

@ -322,7 +322,10 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
wchan = get_wchan(task);
if (lookup_symbol_name(wchan, symname) < 0)
return sprintf(buffer, "%lu", wchan);
if (!ptrace_may_access(task, PTRACE_MODE_READ))
return 0;
else
return sprintf(buffer, "%lu", wchan);
else
return sprintf(buffer, "%s", symname);
}