Messages in this thread Patch in this message | | | Date | Wed, 30 Aug 2023 16:06:00 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 2/2] ocfs2: Replace strlcpy with strscpy |
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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);
(Also, ew, existing code doesn't include a trailing "\n". Oh well.)
-Kees
-- Kees Cook
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