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Subject[patch] For 2.4: syscall revoke.

Hi,

hopefully this mail isn't lost because of a nervous `d' finger ;^)
Last week I've finished the work on the system call revoke for 2.4 and
done some changes on it suggested by the vendors security list.

Due to the security issue of the syscall revoke, it would nice to see
this patch going in 2.4. This would help to close some open security
issues (e.g. user usage of vcs/vcsa and other devices).

This implementation of sys_revoke not only removes all references
of a block or character special file but also all mmap vma's.

The patch is done for 2.4.0-test9, nevertheless it should apply
to 2.4.0-test10-pre2.


Werner
--- arch/alpha/kernel/entry.S
+++ arch/alpha/kernel/entry.S Thu Oct 5 17:13:27 2000
@@ -837,7 +837,7 @@
.quad alpha_ni_syscall
.quad sys_ioctl
.quad alpha_ni_syscall /* 55 */
- .quad alpha_ni_syscall
+ .quad sys_revoke
.quad sys_symlink
.quad sys_readlink
.quad sys_execve
--- arch/i386/kernel/entry.S
+++ arch/i386/kernel/entry.S Thu Oct 5 17:21:43 2000
@@ -649,6 +649,7 @@
.long SYMBOL_NAME(sys_getdents64) /* 220 */
.long SYMBOL_NAME(sys_fcntl64)
.long SYMBOL_NAME(sys_ni_syscall) /* reserved for TUX */
+ .long SYMBOL_NAME(sys_revoke) /* Should we recycle mpx ? */

/*
* NOTE!! This doesn't have to be exact - we just have
@@ -656,6 +657,6 @@
* entries. Don't panic if you notice that this hasn't
* been shrunk every time we add a new system call.
*/
- .rept NR_syscalls-221
+ .rept NR_syscalls-223
.long SYMBOL_NAME(sys_ni_syscall)
.endr
--- fs/open.c
+++ fs/open.c Tue Oct 10 11:55:46 2000
@@ -846,3 +846,128 @@
}
return -EPERM;
}
+
+/*
+ * The routines below do nothing more than revoke a block or
+ * character special file.
+ */
+
+static int filp_revoke(struct file * filp, struct inode * inode);
+static struct file_operations revoke_file_ops;
+
+asmlinkage int sys_revoke(const char* filename)
+{
+ struct nameidata nd;
+ struct list_head *p;
+ struct super_block *sb;
+ int error = 0;
+
+ error = user_path_walk(filename, &nd);
+ if (error)
+ goto out;
+
+ error = -ENOENT;
+ if (!nd.dentry->d_inode)
+ goto dput_and_out;
+
+#ifndef REVOKE_DEBUG
+ error = -EINVAL;
+ if (!S_ISCHR(nd.dentry->d_inode->i_mode) &&
+ !S_ISBLK(nd.dentry->d_inode->i_mode))
+ goto dput_and_out;
+#endif
+
+ error = -EPERM;
+ if ((current->fsuid != nd.dentry->d_inode->i_uid) ||
+ !capable(CAP_FOWNER))
+ goto dput_and_out;
+
+ error = 0;
+ sb = nd.dentry->d_inode->i_sb;
+ file_list_lock();
+ for (p = sb->s_files.next; p != &sb->s_files; p = p->next) {
+ struct file * filp = list_entry(p, struct file, f_list);
+ struct inode * inode;
+
+ if (!filp || !filp->f_dentry)
+ continue;
+ if (nd.dentry != filp->f_dentry)
+ continue;
+ if (filp->f_op == &revoke_file_ops)
+ continue;
+ if (!(inode = filp->f_dentry->d_inode))
+ continue;
+
+ error = filp_revoke(filp, inode);
+ }
+ file_list_unlock();
+dput_and_out:
+ path_release(&nd);
+out:
+ return error;
+}
+
+static int return_EBADF(void) { return -EBADF; }
+#define EBADF_ERROR ((void *) (return_EBADF))
+
+static ssize_t revoke_read (struct file * filp, char * buf, size_t count,
+ loff_t *ppos)
+{
+ return (ssize_t)0;
+}
+
+static int revoke_release (struct inode * inode, struct file * filp)
+{
+ fops_put(filp->f_op);
+ filp->f_op = NULL;
+ return 0;
+}
+
+static ssize_t revoke_readv (struct file *filp, const struct iovec *iov,
+ unsigned long count, loff_t *ppos)
+{
+ return (ssize_t)0;
+}
+
+static struct file_operations revoke_file_ops = {
+ owner: THIS_MODULE,
+ llseek: EBADF_ERROR,
+ read: revoke_read,
+ write: EBADF_ERROR,
+ readdir: EBADF_ERROR,
+ poll: EBADF_ERROR,
+ ioctl: EBADF_ERROR,
+ mmap: EBADF_ERROR,
+ open: EBADF_ERROR,
+ flush: EBADF_ERROR,
+ release: revoke_release,
+ fsync: EBADF_ERROR,
+ fasync: EBADF_ERROR,
+ lock: EBADF_ERROR,
+ readv: revoke_readv,
+ writev: EBADF_ERROR
+};
+
+static int filp_revoke(struct file * filp, struct inode * inode)
+{
+ struct file_operations * fops = filp->f_op;
+ int error = 0;
+
+ down(&inode->i_sem);
+ if (!fops || !file_count(filp))
+ goto truncate_and_out;
+
+ filp->f_op = &revoke_file_ops;
+
+ if (fops->flush)
+ (void) fops->flush(filp);
+ if (fops->release)
+ error = fops->release(inode, filp);
+ fops_put(fops);
+
+truncate_and_out:
+ vmtruncate(inode, (loff_t)0);
+ up(&inode->i_sem);
+
+ return error;
+}
--- include/asm-alpha/unistd.h
+++ include/asm-alpha/unistd.h Thu Oct 5 17:20:03 2000
@@ -57,7 +57,8 @@

#define __NR_ioctl 54
#define __NR_osf_reboot 55 /* not implemented */
-#define __NR_osf_revoke 56 /* not implemented */
+#define __NR_revoke 56
+#define __NR_osf_revoke 56 /* alias for revoke */
#define __NR_symlink 57
#define __NR_readlink 58
#define __NR_execve 59
--- include/asm-i386/unistd.h
+++ include/asm-i386/unistd.h Thu Oct 5 17:18:58 2000
@@ -227,6 +227,8 @@
#define __NR_madvise1 219 /* delete when C lib stub is removed */
#define __NR_getdents64 220
#define __NR_fcntl64 221
+/* #define __NR_tux 222 */
+#define __NR_revoke 223

/* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */
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