Re: [Bug 217238] New: Creating shared read-only map is denied after add write seal to a memfd

[Andrew Morton <akpm@linux-foundation.org>]

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On Fri, 24 Mar 2023 03:34:23 +0000 bugzilla-daemon@kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=217238
> 
>             Bug ID: 217238
>            Summary: Creating shared read-only map is denied after add
>                     write seal to a memfd
>            Product: Memory Management
>            Version: 2.5
>     Kernel Version: 6.2.8
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Other
>           Assignee: akpm@linux-foundation.org
>           Reporter: yshuiv7@gmail.com
>         Regression: No
> 
> Test case:
> 
>     int main() {
>       int fd = memfd_create("test", MFD_ALLOW_SEALING);
>       write(fd, "test", 4);
>       fcntl(fd, F_ADD_SEALS, F_SEAL_WRITE);
> 
>       void *ret = mmap(NULL, 4, PROT_READ, MAP_SHARED, fd, 0);
>     }
> 
> This fails with EPERM. This is in contradiction with what's described in the
> documentation of F_SEAL_WRITE.
> 
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