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Message-ID: <20211116161817.GP7074@brightrain.aerifal.cx>
Date: Tue, 16 Nov 2021 11:18:17 -0500
From: Rich Felker <dalias@...c.org>
To: "Minqiang Chen (ptpt52)" <ptpt52@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: BUG fix: mmap pass wrong offset to kernel
On Tue, Nov 16, 2021 at 11:56:57AM +0800, Minqiang Chen (ptpt52) wrote:
> From 146066a9794b8e39c53337b71a8476b86e79e7d4 Mon Sep 17 00:00:00 2001
> From: Chen Minqiang <ptpt52@...il.com>
> Date: Mon, 16 Oct 2017 08:57:41 +0800
> Subject: [PATCH] musl: fix mmap pass wrong offset to kernel
>
> on 32bit platform for example off_t x=0x8d9eb000, the x/4096 result
> is 0xfff8d9eb, but the sys_mmap2() is expecting 0x8d9eb to be pass to
>
> this happens on 32bit platform or 64bit platform when
> x > = 0x80000000 (32bit platform)
> or
> x > = 0x8000000000000000 (64bit platform)
>
> Signed-off-by: Chen Minqiang <ptpt52@...il.com>
> ---
> src/mman/mmap.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/mman/mmap.c b/src/mman/mmap.c
> index eff88d82..f225cdbb 100644
> --- a/src/mman/mmap.c
> +++ b/src/mman/mmap.c
> @@ -26,7 +26,7 @@ void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off)
> __vm_wait();
> }
> #ifdef SYS_mmap2
> - ret = __syscall(SYS_mmap2, start, len, prot, flags, fd, off/UNIT);
> + ret = __syscall(SYS_mmap2, start, len, prot, flags, fd, (unsigned long)off/UNIT);
> #else
> ret = __syscall(SYS_mmap, start, len, prot, flags, fd, off);
> #endif
> --
> 2.17.1
This patch is wrong and truncates offsets over 32-bit (drops all the
high bits). There is a bug here, but it's just that UNIT has the wrong
type. commit b5bbe797493ea732d4cac15619753c545ed392af introduced the
regression by making UNIT have type unsigned long long. It should have
a small signed type; just int is fine.
Rich
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