lkml.org 
[lkml]   [2023]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 2/2] ocfs2: Replace strlcpy with strscpy
    On Thu, Aug 31, 2023 at 03:28:32PM -0400, Azeem Shaikh wrote:
    > On Wed, Aug 30, 2023 at 7:06 PM Kees Cook <keescook@chromium.org> wrote:
    > >
    > > On Wed, Aug 30, 2023 at 09:54:26PM +0000, Azeem Shaikh wrote:
    > > > strlcpy() reads the entire source buffer first.
    > > > This read may exceed the destination size limit.
    > > > This is both inefficient and can lead to linear read
    > > > overflows if a source string is not NUL-terminated [1].
    > > > In an effort to remove strlcpy() completely [2], replace
    > > > strlcpy() here with strscpy().
    > > >
    > > > Direct replacement is assumed to be safe here since
    > > > it's ok for `kernel_param_ops.get()` to return -errno [3].
    > > > This changes the behavior such that instead of silently ignoring the
    > > > case when sizeof(@buffer) < DLMFS_CAPABILITIES, we now return error.
    > > >
    > > > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
    > > > [2] https://github.com/KSPP/linux/issues/89
    > > > [3] https://elixir.bootlin.com/linux/v6.5/source/include/linux/moduleparam.h#L52
    > > >
    > > > Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
    > > > ---
    > > > fs/ocfs2/dlmfs/dlmfs.c | 2 +-
    > > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > > >
    > > > diff --git a/fs/ocfs2/dlmfs/dlmfs.c b/fs/ocfs2/dlmfs/dlmfs.c
    > > > index 33e529de93b2..b001eccdd2f3 100644
    > > > --- a/fs/ocfs2/dlmfs/dlmfs.c
    > > > +++ b/fs/ocfs2/dlmfs/dlmfs.c
    > > > @@ -80,7 +80,7 @@ static int param_set_dlmfs_capabilities(const char *val,
    > > > static int param_get_dlmfs_capabilities(char *buffer,
    > > > const struct kernel_param *kp)
    > > > {
    > > > - return strlcpy(buffer, DLMFS_CAPABILITIES,
    > > > + return strscpy(buffer, DLMFS_CAPABILITIES,
    > > > strlen(DLMFS_CAPABILITIES) + 1);
    > > > }
    > >
    > > This is another case of "accidentally correct".
    > >
    > >
    > > param->get() is hooked here, in the sysfs "show" callback:
    > >
    > > static ssize_t param_attr_show(struct module_attribute *mattr,
    > > struct module_kobject *mk, char *buf)
    > > {
    > > int count;
    > > struct param_attribute *attribute = to_param_attr(mattr);
    > >
    > > if (!attribute->param->ops->get)
    > > return -EPERM;
    > >
    > > kernel_param_lock(mk->mod);
    > > count = attribute->param->ops->get(buf, attribute->param);
    > > kernel_param_unlock(mk->mod);
    > > return count;
    > > }
    > >
    > > Meaning ultimately this will show up here, if I'm reading names right:
    > > /sys/module/ocfs/parameters/dlmfs_capabilities
    > >
    > > Anyway, the "count" being returned would be quite bad if
    > > DLMFS_CAPABILITIES were dynamic and larger than PAGE_SIZE (the size of
    > > the sysfs buffer).
    > >
    > > For this case, I would say replace strlcpy with sysfs_emit:
    > >
    > > return sysfs_emit(buffer, DLMFS_CAPABILITIES);
    > >
    >
    > Thanks, sending out a v2 for this. Out of curiosity - why sysfs_emit?
    > Is it because DLMFS_CAPABILITIES is a hard-coded string?

    It's basically that sysfs_emit() Does The Right Thing for these
    callbacks: it tracks the offset of the buffer and checks for buffer
    overflow. (All the sysfs callback work on a page-aligned page-sized
    buffer, and the API lacks any length info -- it's "understood" to be
    page-sized.) So, since this is doing a string copy into what is
    ultimately a sysfs buffer, it's best to use sysfs_emit().

    --
    Kees Cook

    \
     
     \ /
      Last update: 2023-08-31 23:05    [W:4.996 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site