snprintf() should be given the full buffer size, not one less. And it
guarantees nul-termination, so doing it manually afterwards is
pointless.
It's even potentially harmful (though probably not in practice because
CPER_REC_LEN is 256), due to the "return how much would have been
written had the buffer been big enough" semantics. I.e., if the bank
and/or device strings are long enough that the "DIMM location ..."
output gets truncated, writing to msg[n] is a buffer overflow.
Signed-off-by: Rasmus Villemoes <[email protected]>
---
drivers/firmware/efi/cper.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index e15d484b6a5a..ea7ca74fc173 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -276,8 +276,7 @@ static int cper_dimm_err_location(struct cper_mem_err_compact *mem, char *msg)
if (!msg || !(mem->validation_bits & CPER_MEM_VALID_MODULE_HANDLE))
return 0;
- n = 0;
- len = CPER_REC_LEN - 1;
+ len = CPER_REC_LEN;
dmi_memdev_name(mem->mem_dev_handle, &bank, &device);
if (bank && device)
n = snprintf(msg, len, "DIMM location: %s %s ", bank, device);
@@ -286,7 +285,6 @@ static int cper_dimm_err_location(struct cper_mem_err_compact *mem, char *msg)
"DIMM location: not present. DMI handle: 0x%.4x ",
mem->mem_dev_handle);
- msg[n] = '\0';
return n;
}
--
2.29.2
On Wed, 21 Apr 2021 at 21:46, Rasmus Villemoes <[email protected]> wrote:
>
> snprintf() should be given the full buffer size, not one less. And it
> guarantees nul-termination, so doing it manually afterwards is
> pointless.
>
> It's even potentially harmful (though probably not in practice because
> CPER_REC_LEN is 256), due to the "return how much would have been
> written had the buffer been big enough" semantics. I.e., if the bank
> and/or device strings are long enough that the "DIMM location ..."
> output gets truncated, writing to msg[n] is a buffer overflow.
>
> Signed-off-by: Rasmus Villemoes <[email protected]>
> ---
> drivers/firmware/efi/cper.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
> index e15d484b6a5a..ea7ca74fc173 100644
> --- a/drivers/firmware/efi/cper.c
> +++ b/drivers/firmware/efi/cper.c
> @@ -276,8 +276,7 @@ static int cper_dimm_err_location(struct cper_mem_err_compact *mem, char *msg)
> if (!msg || !(mem->validation_bits & CPER_MEM_VALID_MODULE_HANDLE))
> return 0;
>
> - n = 0;
> - len = CPER_REC_LEN - 1;
> + len = CPER_REC_LEN;
> dmi_memdev_name(mem->mem_dev_handle, &bank, &device);
> if (bank && device)
> n = snprintf(msg, len, "DIMM location: %s %s ", bank, device);
> @@ -286,7 +285,6 @@ static int cper_dimm_err_location(struct cper_mem_err_compact *mem, char *msg)
> "DIMM location: not present. DMI handle: 0x%.4x ",
> mem->mem_dev_handle);
>
> - msg[n] = '\0';
> return n;
> }
>
> --
> 2.29.2
>
Thanks, I will queue this up.