Messages in this thread | | | From | Azeem Shaikh <> | Date | Thu, 31 Aug 2023 15:28:32 -0400 | Subject | Re: [PATCH 2/2] ocfs2: Replace strlcpy with strscpy |
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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?
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