[Virtio-fs] [PATCH] virtiofsd: Add pread64() to seccomp list for posix_fallocate()

[Virtio-fs] [PATCH] virtiofsd: Add pread64() to seccomp list for posix_fallocate()

[Misono Tomohiro]

I test virtiofs with NFS 4.0 as backend and notice that fallocate
causes system hang (kernel: 5.4-rc1, qemu: virtio-fs-dev branch):
 $ mount -t virtiofs myfs /mnt
 $ dd if=/dev/urandom bs=1000 seek=1 count=1 of=/mnt/file
 $ fallocate -l 2000 /mnt/file # system hang

This is because:
 1. virtiofs supports fallocate syscall while NFS 4.0 does not.
 2. virtiofsd uses posix_fallocate() and it fallbacks to pread64()/
    pwrite64() sequence to reserve blocks if fallocate syscall is
    not available.
 3. pread64() syscall is prohibited by seccomp and virtiofsd thread
    is killed by SIGSYS.

So, just add pread64() to seccomp white list to fix this problem.

Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
---
 contrib/virtiofsd/seccomp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/contrib/virtiofsd/seccomp.c b/contrib/virtiofsd/seccomp.c
index 93b679271d..88b61bca42 100644
--- a/contrib/virtiofsd/seccomp.c
+++ b/contrib/virtiofsd/seccomp.c
@@ -61,6 +61,7 @@ static const int syscall_whitelist[] = {
 	SCMP_SYS(ppoll),
 	SCMP_SYS(prctl), /* TODO restrict to just PR_SET_NAME? */
 	SCMP_SYS(preadv),
+	SCMP_SYS(pread64),
 	SCMP_SYS(pwritev),
 	SCMP_SYS(pwrite64),
 	SCMP_SYS(read),
-- 
2.21.0

Re: [Virtio-fs] [PATCH] virtiofsd: Add pread64() to seccomp list for posix_fallocate()

[Dr. David Alan Gilbert]

* Misono Tomohiro (misono.tomohiro@jp.fujitsu.com) wrote:
> I test virtiofs with NFS 4.0 as backend and notice that fallocate
> causes system hang (kernel: 5.4-rc1, qemu: virtio-fs-dev branch):
>  $ mount -t virtiofs myfs /mnt
>  $ dd if=/dev/urandom bs=1000 seek=1 count=1 of=/mnt/file
>  $ fallocate -l 2000 /mnt/file # system hang
> 
> This is because:
>  1. virtiofs supports fallocate syscall while NFS 4.0 does not.
>  2. virtiofsd uses posix_fallocate() and it fallbacks to pread64()/
>     pwrite64() sequence to reserve blocks if fallocate syscall is
>     not available.
>  3. pread64() syscall is prohibited by seccomp and virtiofsd thread
>     is killed by SIGSYS.
> 
> So, just add pread64() to seccomp white list to fix this problem.
> 
> Signed-off-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>

Thanks, I've squashed this into our seccomp commit.
(It'll be a little while before I push it out, I need to finish a tidyup
I'm doing).

Dave

> ---
>  contrib/virtiofsd/seccomp.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/contrib/virtiofsd/seccomp.c b/contrib/virtiofsd/seccomp.c
> index 93b679271d..88b61bca42 100644
> --- a/contrib/virtiofsd/seccomp.c
> +++ b/contrib/virtiofsd/seccomp.c
> @@ -61,6 +61,7 @@ static const int syscall_whitelist[] = {
>  	SCMP_SYS(ppoll),
>  	SCMP_SYS(prctl), /* TODO restrict to just PR_SET_NAME? */
>  	SCMP_SYS(preadv),
> +	SCMP_SYS(pread64),
>  	SCMP_SYS(pwritev),
>  	SCMP_SYS(pwrite64),
>  	SCMP_SYS(read),
> -- 
> 2.21.0
> 
> _______________________________________________
> Virtio-fs mailing list
> Virtio-fs@redhat.com
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK