From: Morduan Zang <zhangdandan@uniontech.com>
Date: Wed, 14 Jan 2026 05:30:33 +0000 (+0800)
Subject: efi/cper: Fix cper_bits_to_str buffer handling and return value
X-Git-Tag: v5.15.198~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=220a5ee395e0a3a706abdc746e1446d5e4a0e3f2;p=thirdparty%2Fkernel%2Fstable.git

efi/cper: Fix cper_bits_to_str buffer handling and return value

commit d7f1b4bdc7108be1b178e1617b5f45c8918e88d7 upstream.

The return value calculation was incorrect: `return len - buf_size;`
Initially `len = buf_size`, then `len` decreases with each operation.
This results in a negative return value on success.

Fix by returning `buf_size - len` which correctly calculates the actual
number of bytes written.

Fixes: a976d790f494 ("efi/cper: Add a new helper function to print bitmasks")
Signed-off-by: Morduan Zang <zhangdandan@uniontech.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index d0668452dca9e..f00ee3eef71b8 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -161,7 +161,7 @@ int cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
 		len -= size;
 		str += size;
 	}
-	return len - buf_size;
+	return buf_size - len;
 }
 EXPORT_SYMBOL_GPL(cper_bits_to_str);