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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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