On Fri, Feb 23, 2024 at 12:02:22PM -0800, Justin Stitt wrote: > Hi, > > On Wed, Feb 21, 2024 at 6:38 PM Kees Cook <kees@xxxxxxxxxx> wrote: > > > > > > > > On February 21, 2024 4:41:52 PM PST, Justin Stitt <justinstitt@xxxxxxxxxx> wrote: > > >strncpy() is deprecated for use on NUL-terminated destination strings > > >[1] and as such we should prefer more robust and less ambiguous string > > >interfaces. > > > > > >We expect ae->value_string to be NUL-terminated because there's a > > >comment that says as much; these attr strings are also used with other > > >string APIs, further cementing the fact. > > > > > >Now, the question of whether or not to NUL-pad the destination buffer: > > >lpfc_fdmi_rprt_defer() initializes vports (all zero-initialized), then > > >we call lpfc_fdmi_cmd() with each vport and a mask. Then, inside of > > >lpfc_fdmi_cmd() we check each bit in the mask to invoke the proper > > >callback. Importantly, the zero-initialized vport is passed in as the > > >"attr" parameter. Seeing this: > > >| struct lpfc_fdmi_attr_string *ae = attr; > > >... we can tell that ae->value_string is entirely zero-initialized. Due > > >to this, NUL-padding is _not_ required as it would be redundant. > > > > > >Conveniently, strscpy also returns the number of bytes copied into the > > >destination buffer, eliminating the need for strnlen! > > > > > >Considering the above, a suitable replacement is `strscpy` [2]. > > > > > >Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] > > >Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] > > >Link: https://github.com/KSPP/linux/issues/90 > > >Cc: linux-hardening@xxxxxxxxxxxxxxx > > >Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> > > >--- > > > drivers/scsi/lpfc/lpfc_ct.c | 5 ++--- > > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > > >diff --git a/drivers/scsi/lpfc/lpfc_ct.c b/drivers/scsi/lpfc/lpfc_ct.c > > >index baae1f8279e0..42594ec87290 100644 > > >--- a/drivers/scsi/lpfc/lpfc_ct.c > > >+++ b/drivers/scsi/lpfc/lpfc_ct.c > > >@@ -2569,9 +2569,8 @@ lpfc_fdmi_set_attr_string(void *attr, uint16_t attrtype, char *attrstring) > > > * 64 bytes or less. > > > */ > > > > > >- strncpy(ae->value_string, attrstring, sizeof(ae->value_string)); > > >- len = strnlen(ae->value_string, sizeof(ae->value_string)); > > >- /* round string length to a 32bit boundary. Ensure there's a NULL */ > > >+ len = strscpy(ae->value_string, attrstring, sizeof(ae->value_string)); > > > > This could be < 0 on error, and at least lpfc_fdmi_hba_attr_os_ver() may present more than 64 bytes... > > Am I putting too much faith in this comment? > > static inline int lpfc_fdmi_set_attr_string(void *attr, uint16_t > attrtype, char *attrstring) > ... > /* > * We are trusting the caller that if a fdmi string field > * is capped at 64 bytes, the caller passes in a string of > * 64 bytes or less. > */ This comment is clearly wrong, given lpfc_fdmi_hba_attr_os_ver(). :) But I feel like I'm misunderstanding it since it was added by the same commit that added the 256-byte callers, commit 045c58c87560 ("scsi: lpfc: Rework FDMI attribute registration for unintential padding") > > I see lpfc_fdmi_hba_attr_os_ver() calls lpfc_fdmi_set_attr_string() > with an attrstring sized at 256 bytes: > char buf[256] = { 0 }; > > Can we really return -E2BIG from strscpy() if the dest buffer is the > same size as the source buffer? I see my confusion: I didn't check the size of ae->value_string, which I assumed was 64 bytes. But it's 256, so in theory we can't overflow. > I'm happy to just make the standard strncpy -> strscpy replacement and > drop the len assignment. Let me know what you think, Kees. For robustness, let's leave the strlen() in place... -- Kees Cook
