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    SubjectRe: [RFC] link_path_walk cleanup
    Date

    Hi Maneesh,

    The handling of '/' in path_walk() and vfs_follow_link() is broken - if
    the pathname consists entirely of '/' characters, then lookup_parent
    returns the base immediately without setting nd->last. If there's more
    than one '/', then the check for looking up '/' won't be triggered, and
    walk_one() will be called with an undefined nd->last.

    So e.g. running

    ls '//'

    produces

    ls: //: File name too long

    (but I suspect that it could Oops, depending on what was on the stack
    when the nameidata was allocated.)

    Ideally the tests in vfs_follow_link() and path_walk() ought to be
    testing for (nd->last_type == LAST_ROOT), rather than checking
    explicitly for '/' followed by NUL. But that doesn't work, as last_type
    is only set if you include LOOKUP_PARENT in the flags. Setting last_type
    on every path element resolution would probably be unecessary overhead
    given the relative infrequency of looking up "/".

    So the alternative that I suggest is to change lookup_parent() as
    follows:

    while (*name=='/')
    name++;
    if (!*name) {
    nd->last = (struct qstr) { name : ".", len : 1, hash : 0 };
    goto return_base;
    }

    and remove the tests for "/" in vfs_follow_link() and path_walk().
    Setting nd->last to refer to "." will cause walk_one() to return
    immediately, so the zero hash value is OK.

    Paul

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