exec/ptrace: fix get_dumpable() incorrect tests

The get_dumpable() return value is not boolean.  Most users of the
function actually want to be testing for non-SUID_DUMP_USER(1) rather than
SUID_DUMP_DISABLE(0).  The SUID_DUMP_ROOT(2) is also considered a
protected state.  Almost all places did this correctly, excepting the two
places fixed in this patch.

Wrong logic:
    if (dumpable == SUID_DUMP_DISABLE) { /* be protective */ }
        or
    if (dumpable == 0) { /* be protective */ }
        or
    if (!dumpable) { /* be protective */ }

Correct logic:
    if (dumpable != SUID_DUMP_USER) { /* be protective */ }
        or
    if (dumpable != 1) { /* be protective */ }

Without this patch, if the system had set the sysctl fs/suid_dumpable=2, a
user was able to ptrace attach to processes that had dropped privileges to
that user.  (This may have been partially mitigated if Yama was enabled.)

The macros have been moved into the file that declares get/set_dumpable(),
which means things like the ia64 code can see them too.

CVE-2013-2929

Reported-by: Vasily Kulikov <segoon@openwall.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/ia64/include/asm/processor.h b/arch/ia64/include/asm/processor.h
index e0a899a1a8a665c140dba6255dbbde7528a16c79..5a84b3a5074158d8b0fe975d5def50689c8c735d 100644 (file)
--- a/arch/ia64/include/asm/processor.h
+++ b/arch/ia64/include/asm/processor.h
@@ -319,7 +319,7 @@ struct thread_struct {
        regs->loadrs = 0;                                                                       \
        regs->r8 = get_dumpable(current->mm);   /* set "don't zap registers" flag */            \
        regs->r12 = new_sp - 16;        /* allocate 16 byte scratch area */                     \
-       if (unlikely(!get_dumpable(current->mm))) {                                                     \
+       if (unlikely(get_dumpable(current->mm) != SUID_DUMP_USER)) {    \
                /*                                                                              \
                 * Zap scratch regs to avoid leaking bits between processes with different      \
                 * uid/privileges.                                                              \

diff --git a/fs/exec.c b/fs/exec.c
index 2ea437e5acf4d9b0064b48c900d3fa1597573e3b..12120620f0409660555aec739e5c0441abb995ee 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1669,6 +1669,12 @@ int __get_dumpable(unsigned long mm_flags)
        return (ret > SUID_DUMP_USER) ? SUID_DUMP_ROOT : ret;
 }
 
+/*
+ * This returns the actual value of the suid_dumpable flag. For things
+ * that are using this for checking for privilege transitions, it must
+ * test against SUID_DUMP_USER rather than treating it as a boolean
+ * value.
+ */
 int get_dumpable(struct mm_struct *mm)
 {
        return __get_dumpable(mm->flags);

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index e8112ae5053131c47a1e472985fc1628ddd5e8eb..7554fd410bcc35ff1a4d56e1e3ae99c62a78bcad 100644 (file)
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -99,9 +99,6 @@ extern void setup_new_exec(struct linux_binprm * bprm);
 extern void would_dump(struct linux_binprm *, struct file *);
 
 extern int suid_dumpable;
-#define SUID_DUMP_DISABLE      0       /* No setuid dumping */
-#define SUID_DUMP_USER         1       /* Dump as user of process */
-#define SUID_DUMP_ROOT         2       /* Dump as root */
 
 /* Stack area protections */
 #define EXSTACK_DEFAULT   0    /* Whatever the arch defaults to */

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5e226fe3e512b7d08dd55414cce24be1428f5f71..f7efc86046522c2722501f5967d65983162fa78e 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -323,6 +323,10 @@ static inline void arch_pick_mmap_layout(struct mm_struct *mm) {}
 extern void set_dumpable(struct mm_struct *mm, int value);
 extern int get_dumpable(struct mm_struct *mm);
 
+#define SUID_DUMP_DISABLE      0       /* No setuid dumping */
+#define SUID_DUMP_USER         1       /* Dump as user of process */
+#define SUID_DUMP_ROOT         2       /* Dump as root */
+
 /* mm flags */
 /* dumpable bits */
 #define MMF_DUMPABLE      0  /* core dump is permitted */

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index dd562e9aa2c8419b02067c4883c674989a694cd2..1f4bcb3cc21cee5bcfd1b4e13a77eeff2af23a2b 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -257,7 +257,8 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
        if (task->mm)
                dumpable = get_dumpable(task->mm);
        rcu_read_lock();
-       if (!dumpable && !ptrace_has_cap(__task_cred(task)->user_ns, mode)) {
+       if (dumpable != SUID_DUMP_USER &&
+           !ptrace_has_cap(__task_cred(task)->user_ns, mode)) {
                rcu_read_unlock();
                return -EPERM;
        }