The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 1e9d74660d4df625b0889e77018f9e94727ceacd Mon Sep 17 00:00:00 2001 From: Yafang Shao laoar.shao@gmail.com Date: Sat, 8 Jan 2022 13:46:23 +0000 Subject: [PATCH] bpf: Fix mount source show for bpffs
We noticed our tc ebpf tools can't start after we upgrade our in-house kernel version from 4.19 to 5.10. That is because of the behaviour change in bpffs caused by commit d2935de7e4fd ("vfs: Convert bpf to use the new mount API").
In our tc ebpf tools, we do strict environment check. If the environment is not matched, we won't allow to start the ebpf progs. One of the check is whether bpffs is properly mounted. The mount information of bpffs in kernel-4.19 and kernel-5.10 are as follows:
- kernel 4.19 $ mount -t bpf bpffs /sys/fs/bpf $ mount -t bpf bpffs on /sys/fs/bpf type bpf (rw,relatime)
- kernel 5.10 $ mount -t bpf bpffs /sys/fs/bpf $ mount -t bpf none on /sys/fs/bpf type bpf (rw,relatime)
The device name in kernel-5.10 is displayed as none instead of bpffs, then our environment check fails. Currently we modify the tools to adopt to the kernel behaviour change, but I think we'd better change the kernel code to keep the behavior consistent.
After this change, the mount information will be displayed the same with the behavior in kernel-4.19, for example:
$ mount -t bpf bpffs /sys/fs/bpf $ mount -t bpf bpffs on /sys/fs/bpf type bpf (rw,relatime)
Fixes: d2935de7e4fd ("vfs: Convert bpf to use the new mount API") Suggested-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Yafang Shao laoar.shao@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Christian Brauner christian.brauner@ubuntu.com Cc: David Howells dhowells@redhat.com Cc: Al Viro viro@zeniv.linux.org.uk Link: https://lore.kernel.org/bpf/20220108134623.32467-1-laoar.shao@gmail.com
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c index 80da1db47c68..5a8d9f7467bf 100644 --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -648,12 +648,22 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param) int opt;
opt = fs_parse(fc, bpf_fs_parameters, param, &result); - if (opt < 0) + if (opt < 0) { /* We might like to report bad mount options here, but * traditionally we've ignored all mount options, so we'd * better continue to ignore non-existing options for bpf. */ - return opt == -ENOPARAM ? 0 : opt; + if (opt == -ENOPARAM) { + opt = vfs_parse_fs_param_source(fc, param); + if (opt != -ENOPARAM) + return opt; + + return 0; + } + + if (opt < 0) + return opt; + }
switch (opt) { case OPT_MODE: