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![Michael Kerrisk](/assets/img/avatar_default.png)
The POSIX.1 draft spec for utimensat() says: Only a process with the effective user ID equal to the user ID of the file or with appropriate privileges may use futimens() or utimensat() with a non-null times argument that does not have both tv_nsec fields set to UTIME_NOW and does not have both tv_nsec fields set to UTIME_OMIT. If this condition is violated, then the error EPERM should result. However, the current implementation does not generate EPERM if one tv_nsec field is UTIME_NOW while the other is UTIME_OMIT. It should give this error for that case. This patch: a) Repairs that problem. b) Removes the now unneeded nsec_special() helper function. c) Adds some comments to explain the checks that are being performed. Thanks to Miklos, who provided comments on the previous iteration of this patch. As a result, this version is a little simpler and and its logic is better structured. Miklos suggested an alternative idea, migrating the is_owner_or_cap() checks into fs/attr.c:inode_change_ok() via the use of an ATTR_OWNER_CHECK flag. Maybe we could do that later, but for now I've gone with this version, which is IMO simpler, and can be more easily read as being correct. Acked-by: Miklos Szeredi <miklos@szeredi.hu> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
222 lines
5.6 KiB
C
222 lines
5.6 KiB
C
#include <linux/compiler.h>
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#include <linux/file.h>
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#include <linux/fs.h>
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#include <linux/linkage.h>
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#include <linux/mount.h>
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#include <linux/namei.h>
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#include <linux/sched.h>
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#include <linux/stat.h>
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#include <linux/utime.h>
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#include <linux/syscalls.h>
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#include <asm/uaccess.h>
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#include <asm/unistd.h>
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#ifdef __ARCH_WANT_SYS_UTIME
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/*
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* sys_utime() can be implemented in user-level using sys_utimes().
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* Is this for backwards compatibility? If so, why not move it
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* into the appropriate arch directory (for those architectures that
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* need it).
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*/
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/* If times==NULL, set access and modification to current time,
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* must be owner or have write permission.
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* Else, update from *times, must be owner or super user.
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*/
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asmlinkage long sys_utime(char __user *filename, struct utimbuf __user *times)
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{
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struct timespec tv[2];
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if (times) {
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if (get_user(tv[0].tv_sec, ×->actime) ||
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get_user(tv[1].tv_sec, ×->modtime))
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return -EFAULT;
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tv[0].tv_nsec = 0;
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tv[1].tv_nsec = 0;
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}
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return do_utimes(AT_FDCWD, filename, times ? tv : NULL, 0);
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}
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#endif
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static bool nsec_valid(long nsec)
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{
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if (nsec == UTIME_OMIT || nsec == UTIME_NOW)
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return true;
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return nsec >= 0 && nsec <= 999999999;
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}
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/* If times==NULL, set access and modification to current time,
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* must be owner or have write permission.
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* Else, update from *times, must be owner or super user.
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*/
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long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags)
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{
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int error;
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struct nameidata nd;
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struct dentry *dentry;
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struct inode *inode;
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struct iattr newattrs;
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struct file *f = NULL;
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struct vfsmount *mnt;
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error = -EINVAL;
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if (times && (!nsec_valid(times[0].tv_nsec) ||
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!nsec_valid(times[1].tv_nsec))) {
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goto out;
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}
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if (flags & ~AT_SYMLINK_NOFOLLOW)
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goto out;
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if (filename == NULL && dfd != AT_FDCWD) {
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error = -EINVAL;
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if (flags & AT_SYMLINK_NOFOLLOW)
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goto out;
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error = -EBADF;
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f = fget(dfd);
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if (!f)
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goto out;
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dentry = f->f_path.dentry;
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mnt = f->f_path.mnt;
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} else {
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error = __user_walk_fd(dfd, filename, (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW, &nd);
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if (error)
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goto out;
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dentry = nd.path.dentry;
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mnt = nd.path.mnt;
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}
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inode = dentry->d_inode;
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error = mnt_want_write(mnt);
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if (error)
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goto dput_and_out;
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if (times && times[0].tv_nsec == UTIME_NOW &&
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times[1].tv_nsec == UTIME_NOW)
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times = NULL;
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/* In most cases, the checks are done in inode_change_ok() */
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newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
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if (times) {
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error = -EPERM;
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if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
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goto mnt_drop_write_and_out;
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if (times[0].tv_nsec == UTIME_OMIT)
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newattrs.ia_valid &= ~ATTR_ATIME;
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else if (times[0].tv_nsec != UTIME_NOW) {
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newattrs.ia_atime.tv_sec = times[0].tv_sec;
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newattrs.ia_atime.tv_nsec = times[0].tv_nsec;
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newattrs.ia_valid |= ATTR_ATIME_SET;
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}
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if (times[1].tv_nsec == UTIME_OMIT)
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newattrs.ia_valid &= ~ATTR_MTIME;
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else if (times[1].tv_nsec != UTIME_NOW) {
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newattrs.ia_mtime.tv_sec = times[1].tv_sec;
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newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
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newattrs.ia_valid |= ATTR_MTIME_SET;
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}
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/*
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* For the UTIME_OMIT/UTIME_NOW and UTIME_NOW/UTIME_OMIT
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* cases, we need to make an extra check that is not done by
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* inode_change_ok().
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*/
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if (((times[0].tv_nsec == UTIME_NOW &&
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times[1].tv_nsec == UTIME_OMIT)
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||
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(times[0].tv_nsec == UTIME_OMIT &&
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times[1].tv_nsec == UTIME_NOW))
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&& !is_owner_or_cap(inode))
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goto mnt_drop_write_and_out;
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} else {
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/*
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* If times is NULL (or both times are UTIME_NOW),
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* then we need to check permissions, because
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* inode_change_ok() won't do it.
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*/
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error = -EACCES;
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if (IS_IMMUTABLE(inode))
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goto mnt_drop_write_and_out;
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if (!is_owner_or_cap(inode)) {
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if (f) {
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if (!(f->f_mode & FMODE_WRITE))
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goto mnt_drop_write_and_out;
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} else {
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error = vfs_permission(&nd, MAY_WRITE);
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if (error)
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goto mnt_drop_write_and_out;
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}
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}
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}
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mutex_lock(&inode->i_mutex);
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error = notify_change(dentry, &newattrs);
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mutex_unlock(&inode->i_mutex);
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mnt_drop_write_and_out:
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mnt_drop_write(mnt);
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dput_and_out:
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if (f)
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fput(f);
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else
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path_put(&nd.path);
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out:
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return error;
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}
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asmlinkage long sys_utimensat(int dfd, char __user *filename, struct timespec __user *utimes, int flags)
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{
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struct timespec tstimes[2];
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if (utimes) {
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if (copy_from_user(&tstimes, utimes, sizeof(tstimes)))
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return -EFAULT;
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/* Nothing to do, we must not even check the path. */
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if (tstimes[0].tv_nsec == UTIME_OMIT &&
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tstimes[1].tv_nsec == UTIME_OMIT)
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return 0;
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}
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return do_utimes(dfd, filename, utimes ? tstimes : NULL, flags);
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}
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asmlinkage long sys_futimesat(int dfd, char __user *filename, struct timeval __user *utimes)
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{
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struct timeval times[2];
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struct timespec tstimes[2];
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if (utimes) {
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if (copy_from_user(×, utimes, sizeof(times)))
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return -EFAULT;
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/* This test is needed to catch all invalid values. If we
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would test only in do_utimes we would miss those invalid
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values truncated by the multiplication with 1000. Note
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that we also catch UTIME_{NOW,OMIT} here which are only
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valid for utimensat. */
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if (times[0].tv_usec >= 1000000 || times[0].tv_usec < 0 ||
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times[1].tv_usec >= 1000000 || times[1].tv_usec < 0)
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return -EINVAL;
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tstimes[0].tv_sec = times[0].tv_sec;
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tstimes[0].tv_nsec = 1000 * times[0].tv_usec;
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tstimes[1].tv_sec = times[1].tv_sec;
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tstimes[1].tv_nsec = 1000 * times[1].tv_usec;
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}
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return do_utimes(dfd, filename, utimes ? tstimes : NULL, 0);
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}
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asmlinkage long sys_utimes(char __user *filename, struct timeval __user *utimes)
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{
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return sys_futimesat(AT_FDCWD, filename, utimes);
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}
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