From a2982cc922c3068783eb9a1f77a5626a1ec36a1f Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 9 Jun 2016 15:34:02 -0500 Subject: [PATCH] vfs: Generalize filesystem nodev handling. Introduce a function may_open_dev that tests MNT_NODEV and a new superblock flab SB_I_NODEV. Use this new function in all of the places where MNT_NODEV was previously tested. Add the new SB_I_NODEV s_iflag to proc, sysfs, and mqueuefs as those filesystems should never support device nodes, and a simple superblock flags makes that very hard to get wrong. With SB_I_NODEV set if any device nodes somehow manage to show up on on a filesystem those device nodes will be unopenable. Acked-by: Seth Forshee Signed-off-by: "Eric W. Biederman" --- fs/block_dev.c | 2 +- fs/kernfs/mount.c | 4 ++-- fs/namei.c | 8 +++++++- fs/proc/inode.c | 4 ++-- include/linux/fs.h | 2 ++ ipc/mqueue.c | 2 +- 6 files changed, 15 insertions(+), 7 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 71ccab1d22c6..30b8d568203a 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1857,7 +1857,7 @@ struct block_device *lookup_bdev(const char *pathname) if (!S_ISBLK(inode->i_mode)) goto fail; error = -EACCES; - if (path.mnt->mnt_flags & MNT_NODEV) + if (!may_open_dev(&path)) goto fail; error = -ENOMEM; bdev = bd_acquire(inode); diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index 1443df670260..b3d73ad52b22 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -152,8 +152,8 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic) struct dentry *root; info->sb = sb; - /* Userspace would break if executables appear on sysfs */ - sb->s_iflags |= SB_I_NOEXEC; + /* Userspace would break if executables or devices appear on sysfs */ + sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; sb->s_blocksize = PAGE_SIZE; sb->s_blocksize_bits = PAGE_SHIFT; sb->s_magic = magic; diff --git a/fs/namei.c b/fs/namei.c index 6a82fb7e2127..757a32725d92 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2881,6 +2881,12 @@ int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, } EXPORT_SYMBOL(vfs_create); +bool may_open_dev(const struct path *path) +{ + return !(path->mnt->mnt_flags & MNT_NODEV) && + !(path->mnt->mnt_sb->s_iflags & SB_I_NODEV); +} + static int may_open(struct path *path, int acc_mode, int flag) { struct dentry *dentry = path->dentry; @@ -2899,7 +2905,7 @@ static int may_open(struct path *path, int acc_mode, int flag) break; case S_IFBLK: case S_IFCHR: - if (path->mnt->mnt_flags & MNT_NODEV) + if (!may_open_dev(path)) return -EACCES; /*FALLTHRU*/ case S_IFIFO: diff --git a/fs/proc/inode.c b/fs/proc/inode.c index f4817efb25a6..a5b2c33745b7 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -466,8 +466,8 @@ int proc_fill_super(struct super_block *s, void *data, int silent) if (!proc_parse_options(data, ns)) return -EINVAL; - /* User space would break if executables appear on proc */ - s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC; + /* User space would break if executables or devices appear on proc */ + s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV; s->s_flags |= MS_NODIRATIME | MS_NOSUID | MS_NOEXEC; s->s_blocksize = 1024; s->s_blocksize_bits = 10; diff --git a/include/linux/fs.h b/include/linux/fs.h index 9eef64f23a75..e05983170d23 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1327,6 +1327,7 @@ struct mm_struct; /* sb->s_iflags */ #define SB_I_CGROUPWB 0x00000001 /* cgroup-aware writeback enabled */ #define SB_I_NOEXEC 0x00000002 /* Ignore executables on this fs */ +#define SB_I_NODEV 0x00000004 /* Ignore devices on this fs */ /* sb->s_iflags to limit user namespace mounts */ #define SB_I_USERNS_VISIBLE 0x00000010 /* fstype already mounted */ @@ -1602,6 +1603,7 @@ extern int vfs_whiteout(struct inode *, struct dentry *); */ extern void inode_init_owner(struct inode *inode, const struct inode *dir, umode_t mode); +extern bool may_open_dev(const struct path *path); /* * VFS FS_IOC_FIEMAP helper definitions. */ diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 5bdd50de7d05..0b13ace266f2 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -307,7 +307,7 @@ static int mqueue_fill_super(struct super_block *sb, void *data, int silent) struct inode *inode; struct ipc_namespace *ns = sb->s_fs_info; - sb->s_iflags |= SB_I_NOEXEC; + sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV; sb->s_blocksize = PAGE_SIZE; sb->s_blocksize_bits = PAGE_SHIFT; sb->s_magic = MQUEUE_MAGIC; -- 2.20.1