From 991f76f837bf22c5bb07261cfd86525a0a96650c Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 20 Mar 2013 23:25:24 +0800 Subject: sysfs: fix race between readdir and lseek While readdir() is running, lseek() may set filp->f_pos as zero, then may leave filp->private_data pointing to one sysfs_dirent object without holding its reference counter, so the sysfs_dirent object may be used after free in next readdir(). This patch holds inode->i_mutex to avoid the problem since the lock is always held in readdir path. Reported-by: Dave Jones Tested-by: Sasha Levin Cc: Signed-off-by: Ming Lei Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/dir.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'fs/sysfs') diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index 2fbdff6be25c..c9e16608f486 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -1058,10 +1058,21 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir) return 0; } +static loff_t sysfs_dir_llseek(struct file *file, loff_t offset, int whence) +{ + struct inode *inode = file_inode(file); + loff_t ret; + + mutex_lock(&inode->i_mutex); + ret = generic_file_llseek(file, offset, whence); + mutex_unlock(&inode->i_mutex); + + return ret; +} const struct file_operations sysfs_dir_operations = { .read = generic_read_dir, .readdir = sysfs_readdir, .release = sysfs_dir_release, - .llseek = generic_file_llseek, + .llseek = sysfs_dir_llseek, }; -- cgit v1.2.3 From e5110f411d2ee35bf8d202ccca2e89c633060dca Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 20 Mar 2013 23:25:25 +0800 Subject: sysfs: handle failure path correctly for readdir() In case of 'if (filp->f_pos == 0 or 1)' of sysfs_readdir(), the failure from filldir() isn't handled, and the reference counter of the sysfs_dirent object pointed by filp->private_data will be released without clearing filp->private_data, so use after free bug will be triggered later. This patch returns immeadiately under the situation for fixing the bug, and it is reasonable to return from readdir() when filldir() fails. Reported-by: Dave Jones Tested-by: Sasha Levin Cc: Signed-off-by: Ming Lei Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/dir.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/sysfs') diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c index c9e16608f486..e14512678c9b 100644 --- a/fs/sysfs/dir.c +++ b/fs/sysfs/dir.c @@ -1020,6 +1020,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir) ino = parent_sd->s_ino; if (filldir(dirent, ".", 1, filp->f_pos, ino, DT_DIR) == 0) filp->f_pos++; + else + return 0; } if (filp->f_pos == 1) { if (parent_sd->s_parent) @@ -1028,6 +1030,8 @@ static int sysfs_readdir(struct file * filp, void * dirent, filldir_t filldir) ino = parent_sd->s_ino; if (filldir(dirent, "..", 2, filp->f_pos, ino, DT_DIR) == 0) filp->f_pos++; + else + return 0; } mutex_lock(&sysfs_mutex); for (pos = sysfs_dir_pos(ns, parent_sd, filp->f_pos, pos); -- cgit v1.2.3 From 87a8ebd637dafc255070f503909a053cf0d98d3f Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sun, 24 Mar 2013 14:28:27 -0700 Subject: userns: Restrict when proc and sysfs can be mounted Only allow unprivileged mounts of proc and sysfs if they are already mounted when the user namespace is created. proc and sysfs are interesting because they have content that is per namespace, and so fresh mounts are needed when new namespaces are created while at the same time proc and sysfs have content that is shared between every instance. Respect the policy of who may see the shared content of proc and sysfs by only allowing new mounts if there was an existing mount at the time the user namespace was created. In practice there are only two interesting cases: proc and sysfs are mounted at their usual places, proc and sysfs are not mounted at all (some form of mount namespace jail). Cc: stable@vger.kernel.org Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman" --- fs/sysfs/mount.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/sysfs') diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c index 8d924b5ec733..afd83273e6ce 100644 --- a/fs/sysfs/mount.c +++ b/fs/sysfs/mount.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "sysfs.h" @@ -111,6 +112,9 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type, struct super_block *sb; int error; + if (!(flags & MS_KERNMOUNT) && !current_user_ns()->may_mount_sysfs) + return ERR_PTR(-EPERM); + info = kzalloc(sizeof(*info), GFP_KERNEL); if (!info) return ERR_PTR(-ENOMEM); -- cgit v1.2.3