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efi: cper: fix snprintf() use in cper_dimm_err_location()

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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 <linux@rasmusvillemoes.dk>
Fixes: 3760cd2040 ("CPER: Adjust code flow of some functions")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Rasmus Villemoes 2021-04-21 21:46:36 +02:00 committed by Ard Biesheuvel
parent c4039b29fe
commit 942859d969
1 changed files with 1 additions and 3 deletions
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4
drivers/firmware/efi/cper.c
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@ -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;
}