Messages in this thread Patch in this message | | | Subject | [PATCH][SELINUX] Re-open descriptors closed on exec by SELinux to /dev/null | From | Stephen Smalley <> | Date | Mon, 03 May 2004 12:50:14 -0400 |
| |
This patch against 2.6.6-rc3 changes the SELinux module to try to reset any descriptors it closes on exec (due to a lack of permission by the new domain to the inherited open file) to refer to the null device. This counters the problem of SELinux inducing program misbehavior, particularly due to having descriptors 0-2 closed when the new domain is not allowed access to the caller's tty. This is primarily to address the case where the caller is trusted with respect to the new domain, as the untrusted caller case is already handled via AT_SECURE and glibc secure mode. The code is partly based on the OpenWall LSM, which in turn drew from the OpenWall kernel patch. Note that the code does not guarantee that the descriptor is always re-opened to /dev/null; it merely makes a reasonable effort to do so, but can fail under various conditions. Please apply.
security/selinux/hooks.c | 85 ++++++++++++++++++++++- security/selinux/include/flask.h | 3 security/selinux/include/initial_sid_to_string.h | 1 3 files changed, 85 insertions(+), 4 deletions(-)
diff -X /home/sds/dontdiff -ru linux-2.6/security/selinux/hooks.c linux-2.6.new/security/selinux/hooks.c --- linux-2.6/security/selinux/hooks.c 2004-04-30 14:12:43.042622889 -0400 +++ linux-2.6.new/security/selinux/hooks.c 2004-04-30 13:50:48.000000000 -0400 @@ -62,6 +62,7 @@ #include <linux/nfs_mount.h> #include <net/ipv6.h> #include <linux/hugetlb.h> +#include <linux/major.h> #include "avc.h" #include "objsec.h" @@ -1712,18 +1713,77 @@ kfree(bsec); } +/* Create an open file that refers to the null device. + Derived from the OpenWall LSM. */ +struct file *open_devnull(void) +{ + struct inode *inode; + struct dentry *dentry; + struct file *file = NULL; + struct inode_security_struct *isec; + dev_t dev; + + inode = new_inode(current->fs->rootmnt->mnt_sb); + if (!inode) + goto out; + + dentry = dget(d_alloc_root(inode)); + if (!dentry) + goto out_iput; + + file = get_empty_filp(); + if (!file) + goto out_dput; + + dev = MKDEV(MEM_MAJOR, 3); /* null device */ + + inode->i_uid = current->fsuid; + inode->i_gid = current->fsgid; + inode->i_blksize = PAGE_SIZE; + inode->i_blocks = 0; + inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; + inode->i_state = I_DIRTY; /* so that mark_inode_dirty won't touch us */ + + isec = inode->i_security; + isec->sid = SECINITSID_DEVNULL; + isec->sclass = SECCLASS_CHR_FILE; + isec->initialized = 1; + + file->f_flags = O_RDWR; + file->f_mode = FMODE_READ | FMODE_WRITE; + file->f_dentry = dentry; + file->f_vfsmnt = mntget(current->fs->rootmnt); + file->f_pos = 0; + + init_special_inode(inode, S_IFCHR | S_IRUGO | S_IWUGO, dev); + if (inode->i_fop->open(inode, file)) + goto out_fput; + +out: + return file; +out_fput: + mntput(file->f_vfsmnt); + put_filp(file); +out_dput: + dput(dentry); +out_iput: + iput(inode); + file = NULL; + goto out; +} + /* Derived from fs/exec.c:flush_old_files. */ static inline void flush_unauthorized_files(struct files_struct * files) { struct avc_audit_data ad; - struct file *file; + struct file *file, *devnull = NULL; long j = -1; AVC_AUDIT_DATA_INIT(&ad,FS); spin_lock(&files->file_lock); for (;;) { - unsigned long set, i; + unsigned long set, i, fd; j++; i = j * __NFDBITS; @@ -1740,8 +1800,27 @@ continue; if (file_has_perm(current, file, - file_to_av(file))) + file_to_av(file))) { sys_close(i); + fd = get_unused_fd(); + if (fd != i) { + if (fd >= 0) + put_unused_fd(fd); + fput(file); + continue; + } + if (devnull) { + atomic_inc(&devnull->f_count); + } else { + devnull = open_devnull(); + if (!devnull) { + put_unused_fd(fd); + fput(file); + continue; + } + } + fd_install(fd, devnull); + } fput(file); } } diff -X /home/sds/dontdiff -ru linux-2.6/security/selinux/include/flask.h linux-2.6.new/security/selinux/include/flask.h --- linux-2.6/security/selinux/include/flask.h 2003-08-12 09:05:09.000000000 -0400 +++ linux-2.6.new/security/selinux/include/flask.h 2004-04-30 13:47:59.000000000 -0400 @@ -65,7 +65,8 @@ #define SECINITSID_KMOD 24 #define SECINITSID_POLICY 25 #define SECINITSID_SCMP_PACKET 26 +#define SECINITSID_DEVNULL 27 -#define SECINITSID_NUM 26 +#define SECINITSID_NUM 27 #endif diff -X /home/sds/dontdiff -ru linux-2.6/security/selinux/include/initial_sid_to_string.h linux-2.6.new/security/selinux/include/initial_sid_to_string.h --- linux-2.6/security/selinux/include/initial_sid_to_string.h 2003-08-12 09:05:09.000000000 -0400 +++ linux-2.6.new/security/selinux/include/initial_sid_to_string.h 2004-04-30 13:48:10.000000000 -0400 @@ -28,5 +28,6 @@ "kmod", "policy", "scmp_packet", + "devnull", };
-- Stephen Smalley <sds@epoch.ncsc.mil> National Security Agency
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |