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. */ ... 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'm happy to just make the standard strncpy -> strscpy replacement and drop the len assignment. Let me know what you think, Kees. > > -Kees > > > >+ /* round string length to a 32bit boundary */ > > len += (len & 3) ? (4 - (len & 3)) : 4; > > /* size is Type/Len (4 bytes) plus string length */ > > size = FOURBYTES + len; > > > >--- > >base-commit: 39133352cbed6626956d38ed72012f49b0421e7b > >change-id: 20240222-strncpy-drivers-scsi-lpfc-lpfc_ct-c-f54b67eeeb68 > > > >Best regards, > >-- > >Justin Stitt <justinstitt@xxxxxxxxxx> > > > > > > -- > Kees Cook Thanks Justin
