make build_open_flags() treat O_CREAT | O_EXCL as implying O_NOFOLLOW (31d1726d) · Commits · 戴 / test

O_CREAT | O_EXCL means "-EEXIST if we run into a trailing symlink". As it is, we might or might not have LOOKUP_FOLLOW in op->intent in that case - that depends upon having O_NOFOLLOW in open flags. It doesn't matter, since we won't be checking it in that case - do_last() bails out earlier. However, making sure it's not set (i.e. acting as if we had an explicit O_NOFOLLOW) makes the behaviour more explicit and allows to reorder the check for O_CREAT | O_EXCL in do_last() with the call of step_into() immediately following it. Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

+5 −10

Original line number	Diff line number	Diff line
		@@ -3396,22 +3396,17 @@ static int do_last(struct nameidata *nd,
		if (unlikely(error < 0))
		return error;

		/*
		* create/update audit record if it already exists.
		*/
		audit_inode(nd->name, path.dentry, 0);

		if (unlikely((open_flag & (O_EXCL \| O_CREAT)) == (O_EXCL \| O_CREAT))) {
		path_to_nameidata(&path, nd);
		return -EEXIST;
		}

		seq = 0; /* out of RCU mode, so the value doesn't matter */
		inode = d_backing_inode(path.dentry);
		finish_lookup:
		error = step_into(nd, &path, 0, inode, seq);
		if (unlikely(error))
		return error;

		if (unlikely((open_flag & (O_EXCL \| O_CREAT)) == (O_EXCL \| O_CREAT))) {
		audit_inode(nd->name, nd->path.dentry, 0);
		return -EEXIST;
		}
		finish_open:
		/* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */
		error = complete_walk(nd);

fs/open.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1049,8 +1049,10 @@ inline int build_open_flags(const struct open_how how, struct open_flags op)

		if (flags & O_CREAT) {
		op->intent \|= LOOKUP_CREATE;
		if (flags & O_EXCL)
		if (flags & O_EXCL) {
		op->intent \|= LOOKUP_EXCL;
		flags \|= O_NOFOLLOW;
		}
		}

		if (flags & O_DIRECTORY)

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