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SubjectRe: [PATCH] fs: hardlink creation restriction cleanup

* Kees Cook <keescook@chromium.org> wrote:

> Clean-up of hardlink restriction logic, as suggested by Andrew Morton.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> fs/namei.c | 59 +++++++++++++++++++++++++++++++++++++++++------------------
> 1 files changed, 41 insertions(+), 18 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 8ed4e00..a4a21a5 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -693,46 +693,69 @@ static inline int may_follow_link(struct path *link)
> }
>
> /**
> + * safe_hardlink_source - Check for safe hardlink conditions
> + * @inode: the source inode to hardlink from
> + *
> + * Return false if at least one of the following conditions:
> + * - inode is not a regular file
> + * - inode is setuid
> + * - inode is setgid and group-exec
> + * - access failure for read and write
> + *
> + * Otherwise returns true.
> + */
> +static bool safe_hardlink_source(struct inode *inode)
> +{
> + mode_t mode = inode->i_mode;
> +
> + /* Special files should not get pinned to the filesystem. */
> + if (!S_ISREG(mode))
> + return false;
> + /* Setuid files should not get pinned to the filesystem. */
> + if (mode & S_ISUID)
> + return false;
> + /* Executable setgid files should not get pinned to the filesystem. */
> + if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
> + return false;
> + /* Hardlinking to unreadable or unwritable sources is dangerous. */
> + if (inode_permission(inode, MAY_READ | MAY_WRITE))
> + return false;
> +
> + return true;

A really minor nitpick, could we use this form please:

static bool safe_hardlink_source(struct inode *inode)
{
mode_t mode = inode->i_mode;
/* Special files should not get pinned to the filesystem. */
if (!S_ISREG(mode))
return false;
/* Setuid files should not get pinned to the filesystem. */
if (mode & S_ISUID)
return false;
/* Executable setgid files should not get pinned to the filesystem. */
if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
return false;
/* Hardlinking to unreadable or unwritable sources is dangerous. */
if (inode_permission(inode, MAY_READ | MAY_WRITE))
return false;
return true;
}
Those separate blocks of comments and conditions stand out much
nicer this way, making it way easier on the eyes - to my eyes at
least ;-)

Thanks,

Ingo


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