[patch 17/18] proc: avoid information leaks to non-privileged processes

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

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

From: Jake Edge <jake@xxxxxxx>

commit f83ce3e6b02d5e48b3a43b001390e2b58820389d upstream.

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@xxxxxxxxxx>
Signed-off-by: Jake Edge <jake@xxxxxxx>
Acked-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/proc/array.c |   13 +++++++++----
 fs/proc/base.c  |    5 ++++-
 2 files changed, 13 insertions(+), 5 deletions(-)

--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -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>
@@ -347,6 +348,7 @@ static int do_task_stat(struct seq_file 
 	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;
@@ -359,11 +361,14 @@ static int do_task_stat(struct seq_file 
 
 	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);
@@ -419,7 +424,7 @@ static int do_task_stat(struct seq_file 
 		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;
@@ -471,7 +476,7 @@ static int do_task_stat(struct seq_file 
 		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.
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -327,7 +327,10 @@ static int proc_pid_wchan(struct task_st
 	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);
 }


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