From c70f84417429f41519be0197a1092a53c2201f47 Mon Sep 17 00:00:00 2001 From: Michael Kerrisk Date: Mon, 9 Jun 2008 21:16:09 -0700 Subject: [PATCH] [patch for 2.6.26 4/4] vfs: utimensat(): fix write access check for futimens() The POSIX.1 draft spec for futimens()/utimensat() says: Only a process with the effective user ID equal to the user ID of the file, *or with write access to the file*, or with appropriate privileges may use futimens() or utimensat() with a null pointer as the times argument or with both tv_nsec fields set to the special value UTIME_NOW. The important piece here is "with write access to the file", and this matters for futimens(), which deals with an argument that is a file descriptor referring to the file whose timestamps are being updated, The standard is saying that the "writability" check is based on the file permissions, not the access mode with which the file is opened. (This behavior is consistent with the semantics of FreeBSD's futimes().) However, Linux is currently doing the latter -- futimens(fd, times) is a library function implemented as utimensat(fd, NULL, times, 0) and within the utimensat() implementation we have the code: f = fget(dfd); // dfd is 'fd' ... if (f) { if (!(f->f_mode & FMODE_WRITE)) goto mnt_drop_write_and_out; The check should instead be based on the file permissions. Thanks to Miklos for pointing out how to do this check. Miklos also pointed out a simplification that could be made to my first version of this patch, since the checks for the pathname and file descriptor cases can now be conflated. Acked-by: Miklos Szeredi Cc: Al Viro Cc: Ulrich Drepper Signed-off-by: Michael Kerrisk Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- fs/utimes.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/fs/utimes.c b/fs/utimes.c index 118d1c3241b..b6b664e7145 100644 --- a/fs/utimes.c +++ b/fs/utimes.c @@ -148,14 +148,9 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags goto mnt_drop_write_and_out; if (!is_owner_or_cap(inode)) { - if (f) { - if (!(f->f_mode & FMODE_WRITE)) - goto mnt_drop_write_and_out; - } else { - error = vfs_permission(&nd, MAY_WRITE); - if (error) - goto mnt_drop_write_and_out; - } + error = permission(inode, MAY_WRITE, NULL); + if (error) + goto mnt_drop_write_and_out; } } mutex_lock(&inode->i_mutex); -- 2.41.1