[PATCH 6.1 002/280] efi/cper: Fix cper_bits_to_str buffer handling and return value

Greg Kroah-Hartman
2026-02-04T15:03:41Z

From: Morduan Zang <zhangdandan@uniontech.com>

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>
---
drivers/firmware/efi/cper.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- 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_
len -= size;
str += size;
}
- return len - buf_size;
+ return buf_size - len;
}
EXPORT_SYMBOL_GPL(cper_bits_to_str);