[PATCH] net: chelsio: cxgb4: Avoid potential negative array offset

[Kees Cook]

Using min_t(int, ...) as a potential array index implies to the compiler
that negative offsets should be allowed. This is not the case, though.
Replace min_t() with clamp_t(). Fixes the following warning exposed
under future CONFIG_FORTIFY_SOURCE improvements:

In file included from include/linux/string.h:253,
                 from include/linux/bitmap.h:11,
                 from include/linux/cpumask.h:12,
                 from include/linux/smp.h:13,
                 from include/linux/lockdep.h:14,
                 from include/linux/rcupdate.h:29,
                 from include/linux/rculist.h:11,
                 from include/linux/pid.h:5,
                 from include/linux/sched.h:14,
                 from include/linux/delay.h:23,
                 from drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:35:
drivers/net/ethernet/chelsio/cxgb4/t4_hw.c: In function 't4_get_raw_vpd_params':
include/linux/fortify-string.h:46:33: warning: '__builtin_memcpy' pointer overflow between offset 29 and size [2147483648, 4294967295] [-Warray-bounds]
   46 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:388:9: note: in expansion of macro '__underlying_memcpy'
  388 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:433:26: note: in expansion of macro '__fortify_memcpy_chk'
  433 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:2796:9: note: in expansion of macro 'memcpy'
 2796 |         memcpy(p->id, vpd + id, min_t(int, id_len, ID_LEN));
      |         ^~~~~~
include/linux/fortify-string.h:46:33: warning: '__builtin_memcpy' pointer overflow between offset 0 and size [2147483648, 4294967295] [-Warray-bounds]
   46 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:388:9: note: in expansion of macro '__underlying_memcpy'
  388 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:433:26: note: in expansion of macro '__fortify_memcpy_chk'
  433 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:2798:9: note: in expansion of macro 'memcpy'
 2798 |         memcpy(p->sn, vpd + sn, min_t(int, sn_len, SERNUM_LEN));
      |         ^~~~~~

Additionally remove needless cast from u8[] to char * in last strim()
call.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Link: https://lore.kernel.org/lkml/202205031926.FVP7epJM-lkp@xxxxxxxxx
Fixes: fc9279298e3a ("cxgb4: Search VPD with pci_vpd_find_ro_info_keyword()")
Fixes: 24c521f81c30 ("cxgb4: Use pci_vpd_find_id_string() to find VPD ID string")
Cc: Raju Rangoju <rajur@xxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/net/ethernet/chelsio/cxgb4/t4_hw.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
index e7b4e3ed056c..f119ec7323e5 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
@@ -2793,14 +2793,14 @@ int t4_get_raw_vpd_params(struct adapter *adapter, struct vpd_params *p)
 		goto out;
 	na = ret;
 
-	memcpy(p->id, vpd + id, min_t(int, id_len, ID_LEN));
+	memcpy(p->id, vpd + id, clamp_t(int, id_len, 0, ID_LEN));
 	strim(p->id);
-	memcpy(p->sn, vpd + sn, min_t(int, sn_len, SERNUM_LEN));
+	memcpy(p->sn, vpd + sn, clamp_t(int, sn_len, 0, SERNUM_LEN));
 	strim(p->sn);
-	memcpy(p->pn, vpd + pn, min_t(int, pn_len, PN_LEN));
+	memcpy(p->pn, vpd + pn, clamp_t(int, pn_len, 0, PN_LEN));
 	strim(p->pn);
-	memcpy(p->na, vpd + na, min_t(int, na_len, MACADDR_LEN));
-	strim((char *)p->na);
+	memcpy(p->na, vpd + na, clamp_t(int, na_len, 0, MACADDR_LEN));
+	strim(p->na);
 
 out:
 	vfree(vpd);
-- 
2.32.0