proc: avoid leaking eip, esp, or wchan to non-privileged processes Using the same test as is used for /proc/pid/maps and smaps, only allow processes that can ptrace() a given process to access its /proc/pid/wchan and get eip and esp from /proc/pid/stat. 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. Signed-off-by: Jake Edge <jake@xxxxxxx> --- fs/proc/array.c | 11 ++++++++--- fs/proc/base.c | 3 +++ 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 7e4877d..e96d508 100644 --- 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> @@ -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; diff --git a/fs/proc/base.c b/fs/proc/base.c index aa763ab..cd3c0d7 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -319,6 +319,9 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer) unsigned long wchan; char symname[KSYM_NAME_LEN]; + if (!ptrace_may_access(task, PTRACE_MODE_READ)) + return 0; + wchan = get_wchan(task); if (lookup_symbol_name(wchan, symname) < 0) -- 1.6.2.2 -- Jake Edge - LWN - jake@xxxxxxx - http://lwn.net -- 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
