From b287eb85e51a04fb26ad3db1b73a17fbdaa11e17 Mon Sep 17 00:00:00 2001 From: Zhang Zixun Date: Mon, 27 Dec 2021 22:02:49 +0100 Subject: [PATCH] x86/mce/inject: Avoid out-of-bounds write when setting flags [ Upstream commit de768416b203ac84e02a757b782a32efb388476f ] A contrived zero-length write, for example, by using write(2): ... ret = write(fd, str, 0); ... to the "flags" file causes: BUG: KASAN: stack-out-of-bounds in flags_write Write of size 1 at addr ffff888019be7ddf by task writefile/3787 CPU: 4 PID: 3787 Comm: writefile Not tainted 5.16.0-rc7+ #12 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 due to accessing buf one char before its start. Prevent such out-of-bounds access. [ bp: Productize into a proper patch. Link below is the next best thing because the original mail didn't get archived on lore. ] Fixes: 0451d14d0561 ("EDAC, mce_amd_inj: Modify flags attribute to use string arguments") Signed-off-by: Zhang Zixun Signed-off-by: Borislav Petkov Link: https://lore.kernel.org/linux-edac/YcnePfF1OOqoQwrX@zn.tnic/ Signed-off-by: Sasha Levin --- arch/x86/kernel/cpu/mcheck/mce-inject.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce-inject.c b/arch/x86/kernel/cpu/mcheck/mce-inject.c index 94aa91b09c28..2778b66aee8f 100644 --- a/arch/x86/kernel/cpu/mcheck/mce-inject.c +++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c @@ -354,7 +354,7 @@ static ssize_t flags_write(struct file *filp, const char __user *ubuf, char buf[MAX_FLAG_OPT_SIZE], *__buf; int err; - if (cnt > MAX_FLAG_OPT_SIZE) + if (!cnt || cnt > MAX_FLAG_OPT_SIZE) return -EINVAL; if (copy_from_user(&buf, ubuf, cnt)) -- 2.20.1