[PATCH v2 4/8] modpost: fix stack out-of-bounds read for unterminated PNP ids

[Leizhen Zhang <lzsx618@gmail.com>]

do_pnp_device_entry() and do_pnp_card_entry() copy the PNP id into a
local acpi_id[PNP_ID_LEN] buffer to upper-case it, and then print it with
"%s". A PNP id that uses all PNP_ID_LEN characters, e.g. "PNP0C0F1", is
accepted by the compiler without a terminating NUL (the kernel is built
with -Wno-unterminated-string-initialization), so the local copy is not
NUL-terminated and printing it reads past the end of the stack buffer:

  AddressSanitizer: stack-buffer-overflow ... in printf_common
    ... do_pnp_device_entry scripts/mod/file2alias.c

Limit the printed length to the size of the id buffers.

Found by fuzzing modpost with ASan/UBSan.

Fixes: 72638f598ec9 ("PNP: fix broken pnp lowercasing for acpi module aliases")
Assisted-by: Claude:claude-opus-5-5 ASan UBSan
Signed-off-by: Leizhen Zhang <lzsx618@gmail.com>
---
v2:
 - Use my real name in the From and Signed-off-by lines. No code
   changes.

v1: https://lore.kernel.org/r/20261005104050.1786222-6-lzsx618@gmail.com

 scripts/mod/file2alias.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 61a831c187..7685fb5135 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -573,8 +573,9 @@ static void do_pnp_device_entry(struct module *mod, void *symval)
 	/* fix broken pnp bus lowercasing */
 	for (unsigned int i = 0; i < sizeof(acpi_id); i++)
 		acpi_id[i] = toupper((*id)[i]);
-	module_alias_printf(mod, false, "pnp:d%s*", *id);
-	module_alias_printf(mod, false, "acpi*:%s:*", acpi_id);
+	module_alias_printf(mod, false, "pnp:d%.*s*", (int)sizeof(*id), *id);
+	module_alias_printf(mod, false, "acpi*:%.*s:*",
+			    (int)sizeof(acpi_id), acpi_id);
 }
 
 /* looks like: "pnp:dD" for every device of the card */
@@ -594,8 +595,9 @@ static void do_pnp_card_entry(struct module *mod, void *symval)
 			acpi_id[j] = toupper(id[j]);
 
 		/* add an individual alias for every device entry */
-		module_alias_printf(mod, false, "pnp:d%s*", id);
-		module_alias_printf(mod, false, "acpi*:%s:*", acpi_id);
+		module_alias_printf(mod, false, "pnp:d%.*s*", PNP_ID_LEN, id);
+		module_alias_printf(mod, false, "acpi*:%.*s:*",
+				    PNP_ID_LEN, acpi_id);
 	}
 }
 
-- 
2.34.1