efi: cper: fix scnprintf() use in cper_mem_err_location()

The last two if-clauses fail to update n, so whatever they might have
written at &msg[n] would be cut off by the final nul-termination.

That nul-termination is redundant; scnprintf(), just like snprintf(),
guarantees a nul-terminated output buffer, provided the buffer size is
positive.

And there's no need to discount one byte from the initial buffer;
vsnprintf() expects to be given the full buffer size - it's not going
to write the nul-terminator one beyond the given (buffer, size) pair.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index ea7ca74fc1730e021273dcdfc77c8def8f5c8ed6..1cb70976dbe7f6b298440edd56e35a7888cc94bb 100644 (file)
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -221,7 +221,7 @@ static int cper_mem_err_location(struct cper_mem_err_compact *mem, char *msg)
                return 0;
 
        n = 0;
-       len = CPER_REC_LEN - 1;
+       len = CPER_REC_LEN;
        if (mem->validation_bits & CPER_MEM_VALID_NODE)
                n += scnprintf(msg + n, len - n, "node: %d ", mem->node);
        if (mem->validation_bits & CPER_MEM_VALID_CARD)
@@ -258,13 +258,12 @@ static int cper_mem_err_location(struct cper_mem_err_compact *mem, char *msg)
                n += scnprintf(msg + n, len - n, "responder_id: 0x%016llx ",
                               mem->responder_id);
        if (mem->validation_bits & CPER_MEM_VALID_TARGET_ID)
-               scnprintf(msg + n, len - n, "target_id: 0x%016llx ",
-                         mem->target_id);
+               n += scnprintf(msg + n, len - n, "target_id: 0x%016llx ",
+                              mem->target_id);
        if (mem->validation_bits & CPER_MEM_VALID_CHIP_ID)
-               scnprintf(msg + n, len - n, "chip_id: %d ",
-                         mem->extended >> CPER_MEM_CHIP_ID_SHIFT);
+               n += scnprintf(msg + n, len - n, "chip_id: %d ",
+                              mem->extended >> CPER_MEM_CHIP_ID_SHIFT);
 
-       msg[n] = '\0';
        return n;
 }