EDAC/ghes: Set the DIMM label unconditionally

The commit

  cb51a371 ("EDAC/ghes: Setup DIMM label from DMI and use it in error reports")

enforced that both the bank and device strings passed to
dimm_setup_label() are not NULL.

However, there are BIOSes, for example on a

  HPE ProLiant DL360 Gen10/ProLiant DL360 Gen10, BIOS U32 03/15/2019

which don't populate both strings:

  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

This results in a buffer overflow because ghes_edac_register() calls
strlen() on an uninitialized label, which had non-zero values left over
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

The label contains garbage because the commit in Fixes reallocs the
DIMMs array while scanning the system but doesn't clear the newly
allocated memory.

Change dimm_setup_label() to always initialize the label to fix the
issue. Set it to the empty string in case BIOS does not provide both
bank and device so that ghes_edac_register() can keep the default label
given by edac_mc_alloc_dimms().

  [ bp: Rewrite commit message. ]

Fixes: b9cae277 ("EDAC/ghes: Scan the system once on driver init")
Co-developed-by: Robert Richter <rric@kernel.org>
Signed-off-by: Robert Richter <rric@kernel.org>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Robert Elliott <elliott@hpe.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220719220124.760359-1-toshi.kani@hpe.com

drivers/edac/ghes_edac.c

@@ -103,9 +103,14 @@ 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 to a NULL string when both bank and device are zero. In this case,
+	 * the label assigned by default will be preserved.
+	 */
+	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)