CVE-2012-0056 proc: clean up and fix /proc/<pid>/mem (rhbz 782681)

2 files changed, 277 insertions, 0 deletions

diff --git a/kernel.spec b/kernel.spec
index 1da145054..9f7ff0829 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -764,6 +764,9 @@ Patch21074: KVM-x86-fix-missing-checks-in-syscall-emulation.patch
 #rhbz 728740
 Patch21076: rtl8192cu-Fix-WARNING-on-suspend-resume.patch
 
+#rhbz 782681
+Patch21085: proc-clean-up-and-fix-proc-pid-mem-handling.patch
+
 # compat-wireless patches
 Patch50000: compat-wireless-config-fixups.patch
 Patch50001: compat-wireless-pr_fmt-warning-avoidance.patch
@@ -1484,6 +1487,9 @@ ApplyPatch KVM-x86-fix-missing-checks-in-syscall-emulation.patch
 #rhbz 728740
 ApplyPatch rtl8192cu-Fix-WARNING-on-suspend-resume.patch
 
+#rhbz 782681
+ApplyPatch proc-clean-up-and-fix-proc-pid-mem-handling.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -2322,6 +2328,9 @@ fi
 #                 ||----w |
 #                 ||     ||
 %changelog
+* Wed Jan 18 2012 Josh Boyer <jwboyer@redhat.com>
+- CVE-2012-0056 proc: clean up and fix /proc/<pid>/mem (rhbz 782681)
+
 * Tue Jan 17 2012 Dave Jones <davej@redhat.com>
 - Rawhide builds now use MAXSMP on x86.
 - For release builds, set x86-64 to support 64 CPUs.
diff --git a/proc-clean-up-and-fix-proc-pid-mem-handling.patch b/proc-clean-up-and-fix-proc-pid-mem-handling.patch
new file mode 100644
index 000000000..c793475d2
--- /dev/null
+++ b/proc-clean-up-and-fix-proc-pid-mem-handling.patch
@@ -0,0 +1,268 @@
+From e268337dfe26dfc7efd422a804dbb27977a3cccc Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Tue, 17 Jan 2012 15:21:19 -0800
+Subject: [PATCH] proc: clean up and fix /proc/<pid>/mem handling
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+Jüri Aedla reported that the /proc/<pid>/mem handling really isn't very
+robust, and it also doesn't match the permission checking of any of the
+other related files.
+
+This changes it to do the permission checks at open time, and instead of
+tracking the process, it tracks the VM at the time of the open.  That
+simplifies the code a lot, but does mean that if you hold the file
+descriptor open over an execve(), you'll continue to read from the _old_
+VM.
+
+That is different from our previous behavior, but much simpler.  If
+somebody actually finds a load where this matters, we'll need to revert
+this commit.
+
+I suspect that nobody will ever notice - because the process mapping
+addresses will also have changed as part of the execve.  So you cannot
+actually usefully access the fd across a VM change simply because all
+the offsets for IO would have changed too.
+
+Reported-by: Jüri Aedla <asd@ut.ee>
+Cc: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+---
+ fs/proc/base.c |  145 +++++++++++++++-----------------------------------------
+ 1 files changed, 39 insertions(+), 106 deletions(-)
+
+diff --git a/fs/proc/base.c b/fs/proc/base.c
+index 5485a53..662ddf2 100644
+--- a/fs/proc/base.c
++++ b/fs/proc/base.c
+@@ -198,65 +198,7 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
+ 	return result;
+ }
+ 
+-static struct mm_struct *__check_mem_permission(struct task_struct *task)
+-{
+-	struct mm_struct *mm;
+-
+-	mm = get_task_mm(task);
+-	if (!mm)
+-		return ERR_PTR(-EINVAL);
+-
+-	/*
+-	 * A task can always look at itself, in case it chooses
+-	 * to use system calls instead of load instructions.
+-	 */
+-	if (task == current)
+-		return mm;
+-
+-	/*
+-	 * If current is actively ptrace'ing, and would also be
+-	 * permitted to freshly attach with ptrace now, permit it.
+-	 */
+-	if (task_is_stopped_or_traced(task)) {
+-		int match;
+-		rcu_read_lock();
+-		match = (ptrace_parent(task) == current);
+-		rcu_read_unlock();
+-		if (match && ptrace_may_access(task, PTRACE_MODE_ATTACH))
+-			return mm;
+-	}
+-
+-	/*
+-	 * No one else is allowed.
+-	 */
+-	mmput(mm);
+-	return ERR_PTR(-EPERM);
+-}
+-
+-/*
+- * If current may access user memory in @task return a reference to the
+- * corresponding mm, otherwise ERR_PTR.
+- */
+-static struct mm_struct *check_mem_permission(struct task_struct *task)
+-{
+-	struct mm_struct *mm;
+-	int err;
+-
+-	/*
+-	 * Avoid racing if task exec's as we might get a new mm but validate
+-	 * against old credentials.
+-	 */
+-	err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+-	if (err)
+-		return ERR_PTR(err);
+-
+-	mm = __check_mem_permission(task);
+-	mutex_unlock(&task->signal->cred_guard_mutex);
+-
+-	return mm;
+-}
+-
+-struct mm_struct *mm_for_maps(struct task_struct *task)
++static struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
+ {
+ 	struct mm_struct *mm;
+ 	int err;
+@@ -267,7 +209,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
+ 
+ 	mm = get_task_mm(task);
+ 	if (mm && mm != current->mm &&
+-			!ptrace_may_access(task, PTRACE_MODE_READ)) {
++			!ptrace_may_access(task, mode)) {
+ 		mmput(mm);
+ 		mm = ERR_PTR(-EACCES);
+ 	}
+@@ -276,6 +218,11 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
+ 	return mm;
+ }
+ 
++struct mm_struct *mm_for_maps(struct task_struct *task)
++{
++	return mm_access(task, PTRACE_MODE_READ);
++}
++
+ static int proc_pid_cmdline(struct task_struct *task, char * buffer)
+ {
+ 	int res = 0;
+@@ -752,38 +699,39 @@ static const struct file_operations proc_single_file_operations = {
+ 
+ static int mem_open(struct inode* inode, struct file* file)
+ {
+-	file->private_data = (void*)((long)current->self_exec_id);
++	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
++	struct mm_struct *mm;
++
++	if (!task)
++		return -ESRCH;
++
++	mm = mm_access(task, PTRACE_MODE_ATTACH);
++	put_task_struct(task);
++
++	if (IS_ERR(mm))
++		return PTR_ERR(mm);
++
+ 	/* OK to pass negative loff_t, we can catch out-of-range */
+ 	file->f_mode |= FMODE_UNSIGNED_OFFSET;
++	file->private_data = mm;
++
+ 	return 0;
+ }
+ 
+ static ssize_t mem_read(struct file * file, char __user * buf,
+ 			size_t count, loff_t *ppos)
+ {
+-	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
++	int ret;
+ 	char *page;
+ 	unsigned long src = *ppos;
+-	int ret = -ESRCH;
+-	struct mm_struct *mm;
++	struct mm_struct *mm = file->private_data;
+ 
+-	if (!task)
+-		goto out_no_task;
++	if (!mm)
++		return 0;
+ 
+-	ret = -ENOMEM;
+ 	page = (char *)__get_free_page(GFP_TEMPORARY);
+ 	if (!page)
+-		goto out;
+-
+-	mm = check_mem_permission(task);
+-	ret = PTR_ERR(mm);
+-	if (IS_ERR(mm))
+-		goto out_free;
+-
+-	ret = -EIO;
+- 
+-	if (file->private_data != (void*)((long)current->self_exec_id))
+-		goto out_put;
++		return -ENOMEM;
+ 
+ 	ret = 0;
+  
+@@ -810,13 +758,7 @@ static ssize_t mem_read(struct file * file, char __user * buf,
+ 	}
+ 	*ppos = src;
+ 
+-out_put:
+-	mmput(mm);
+-out_free:
+ 	free_page((unsigned long) page);
+-out:
+-	put_task_struct(task);
+-out_no_task:
+ 	return ret;
+ }
+ 
+@@ -825,27 +767,15 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
+ {
+ 	int copied;
+ 	char *page;
+-	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
+ 	unsigned long dst = *ppos;
+-	struct mm_struct *mm;
++	struct mm_struct *mm = file->private_data;
+ 
+-	copied = -ESRCH;
+-	if (!task)
+-		goto out_no_task;
++	if (!mm)
++		return 0;
+ 
+-	copied = -ENOMEM;
+ 	page = (char *)__get_free_page(GFP_TEMPORARY);
+ 	if (!page)
+-		goto out_task;
+-
+-	mm = check_mem_permission(task);
+-	copied = PTR_ERR(mm);
+-	if (IS_ERR(mm))
+-		goto out_free;
+-
+-	copied = -EIO;
+-	if (file->private_data != (void *)((long)current->self_exec_id))
+-		goto out_mm;
++		return -ENOMEM;
+ 
+ 	copied = 0;
+ 	while (count > 0) {
+@@ -869,13 +799,7 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
+ 	}
+ 	*ppos = dst;
+ 
+-out_mm:
+-	mmput(mm);
+-out_free:
+ 	free_page((unsigned long) page);
+-out_task:
+-	put_task_struct(task);
+-out_no_task:
+ 	return copied;
+ }
+ 
+@@ -895,11 +819,20 @@ loff_t mem_lseek(struct file *file, loff_t offset, int orig)
+ 	return file->f_pos;
+ }
+ 
++static int mem_release(struct inode *inode, struct file *file)
++{
++	struct mm_struct *mm = file->private_data;
++
++	mmput(mm);
++	return 0;
++}
++
+ static const struct file_operations proc_mem_operations = {
+ 	.llseek		= mem_lseek,
+ 	.read		= mem_read,
+ 	.write		= mem_write,
+ 	.open		= mem_open,
++	.release	= mem_release,
+ };
+ 
+ static ssize_t environ_read(struct file *file, char __user *buf,
+-- 
+1.7.7.5
+