* [musl] BUG fix: mmap pass wrong offset to kernel
@ 2021-11-16 3:56 Minqiang Chen (ptpt52)
2021-11-16 16:18 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: Minqiang Chen (ptpt52) @ 2021-11-16 3:56 UTC (permalink / raw)
To: musl
[-- Attachment #1: Type: text/plain, Size: 1177 bytes --]
From 146066a9794b8e39c53337b71a8476b86e79e7d4 Mon Sep 17 00:00:00 2001
From: Chen Minqiang <ptpt52@gmail.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@gmail.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
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [musl] BUG fix: mmap pass wrong offset to kernel
2021-11-16 3:56 [musl] BUG fix: mmap pass wrong offset to kernel Minqiang Chen (ptpt52)
@ 2021-11-16 16:18 ` Rich Felker
2022-01-09 6:00 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: Rich Felker @ 2021-11-16 16:18 UTC (permalink / raw)
To: Minqiang Chen (ptpt52); +Cc: musl
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@gmail.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@gmail.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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [musl] BUG fix: mmap pass wrong offset to kernel
2021-11-16 16:18 ` Rich Felker
@ 2022-01-09 6:00 ` Rich Felker
0 siblings, 0 replies; 3+ messages in thread
From: Rich Felker @ 2022-01-09 6:00 UTC (permalink / raw)
To: Minqiang Chen (ptpt52); +Cc: musl
On Tue, Nov 16, 2021 at 11:18:17AM -0500, Rich Felker wrote:
> 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@gmail.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@gmail.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.
Following up on this again: there isn't actually a bug here. All valid
offsets to mmap are non-negative off_t values, so coercion to unsigned
long long does not alter the value. If the offset is negative, it was
already caught by the mask against OFF_MASK in the first if statement.
Rich
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-01-09 6:00 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-11-16 3:56 [musl] BUG fix: mmap pass wrong offset to kernel Minqiang Chen (ptpt52)
2021-11-16 16:18 ` Rich Felker
2022-01-09 6:00 ` Rich Felker
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