[PATCH v3] EDAC/ghes: Set the DIMM label unconditionally

[Toshi Kani <toshi.kani@hpe.com>]

The following buffer overflow BUG was observed on an HPE system.
ghes_edac_register() called strlen() on an uninitialized label,
which had non-zero values from krealloc_array().

  detected buffer overflow in __fortify_strlen
   ------------[ cut here ]------------
   kernel BUG at lib/string_helpers.c:983!
   invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
   CPU: 1 PID: 1 Comm: swapper/0 Tainted: G          I       5.18.6-200.fc36.x86_64 #1
   Hardware name: HPE ProLiant DL360 Gen10/ProLiant DL360 Gen10, BIOS U32 03/15/2019
   RIP: 0010:fortify_panic
   ...
   Call Trace:
    <TASK>
    ghes_edac_register.cold
    ghes_probe
    platform_probe
    really_probe
    __driver_probe_device
    driver_probe_device
    __driver_attach
    ? __device_attach_driver
    bus_for_each_dev
    bus_add_driver
    driver_register
    acpi_ghes_init
    acpi_init
    ? acpi_sleep_proc_init
    do_one_initcall

dimm_setup_label() only initializes the label when both bank and
device are set.  This HPE BIOS only sets device since bank locator
is unnecessary to locate a DIMM.

  Handle 0x0020, DMI type 17, 84 bytes
  Memory Device
          Array Handle: 0x0013
          Error Information Handle: Not Provided
          Total Width: 72 bits
          Data Width: 64 bits
          Size: 32 GB
          Form Factor: DIMM
          Set: None
          Locator: PROC 1 DIMM 1        <=== device
          Bank Locator: Not Specified   <=== bank

Change dimm_setup_label() to always initialize the label to fix the
issue.  It sets to a null string in case BIOS does not provide both
bank and device so that ghes_edac_register() keeps the default label
from edac_mc_alloc_dimms().

Fixes: b9cae27728d1f ("EDAC/ghes: Scan the system once on driver init")
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Co-developed-by: Robert Richter <rric@kernel.org>
Tested-by: Robert Elliott <elliott@hpe.com>
---
 drivers/edac/ghes_edac.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
index 59b0bedc9c24..c229ed0ce678 100644
--- a/drivers/edac/ghes_edac.c
+++ b/drivers/edac/ghes_edac.c
@@ -103,9 +103,15 @@ static void dimm_setup_label(struct dimm_info *dimm, u16 handle)
 
 	dmi_memdev_name(handle, &bank, &device);
 
-	/* both strings must be non-zero */
-	if (bank && *bank && device && *device)
-		snprintf(dimm->label, sizeof(dimm->label), "%s %s", bank, device);
+	/* 
+	 * Set a null string when both bank and device are zero.
+	 * This keeps ghes_edac_register() preserving the default
+	 * label from edac_mc_alloc_dimms().
+	 */
+	snprintf(dimm->label, sizeof(dimm->label), "%s%s%s",
+			(bank && *bank) ? bank : "",
+			(bank && *bank && device && *device) ? " " : "",
+			(device && *device) ? device : "");
 }
 
 static void assign_dmi_dimm_info(struct dimm_info *dimm, struct memdev_dmi_entry *entry)