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RPC: add wrapper for svc_reserve to account for checksum

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When the kernel calls svc_reserve to downsize the expected size of an RPC
reply, it fails to account for the possibility of a checksum at the end of
the packet.  If a client mounts a NFSv2/3 with sec=krb5i/p, and does I/O
then you'll generally see messages similar to this in the server's ring
buffer:

RPC request reserved 164 but used 208

While I was never able to verify it, I suspect that this problem is also
the root cause of some oopses I've seen under these conditions:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=227726

This is probably also a problem for other sec= types and for NFSv4.  The
large reserved size for NFSv4 compound packets seems to generally paper
over the problem, however.

This patch adds a wrapper for svc_reserve that accounts for the possibility
of a checksum.  It also fixes up the appropriate callers of svc_reserve to
call the wrapper.  For now, it just uses a hardcoded value that I
determined via testing.  That value may need to be revised upward as things
change, or we may want to eventually add a new auth_op that attempts to
calculate this somehow.

Unfortunately, there doesn't seem to be a good way to reliably determine
the expected checksum length prior to actually calculating it, particularly
with schemes like spkm3.

Signed-off-by: Jeff Layton <[email protected]>
Acked-by: Neil Brown <[email protected]>
Cc: Trond Myklebust <[email protected]>
Acked-by: J. Bruce Fields <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Jeff Layton 2007-05-09 02:34:50 -07:00 • committed by Linus Torvalds
commit cd123012d9
4 changed files with 22 additions and 3 deletions
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2
fs/nfsd/nfs3proc.c
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@ -177,7 +177,7 @@ nfsd3_proc_read(struct svc_rqst *rqstp, struct nfsd3_readargs *argp,
if (max_blocksize < resp->count)
resp->count = max_blocksize;
svc_reserve(rqstp, ((1 + NFS3_POST_OP_ATTR_WORDS + 3)<<2) + resp->count +4);
svc_reserve_auth(rqstp, ((1 + NFS3_POST_OP_ATTR_WORDS + 3)<<2) + resp->count +4);
fh_copy(&resp->fh, &argp->fh);
nfserr = nfsd_read(rqstp, &resp->fh, NULL,

2
fs/nfsd/nfsproc.c
View file

@ -155,7 +155,7 @@ nfsd_proc_read(struct svc_rqst *rqstp, struct nfsd_readargs *argp,
argp->count);
argp->count = NFSSVC_MAXBLKSIZE_V2;
}
svc_reserve(rqstp, (19<<2) + argp->count + 4);
svc_reserve_auth(rqstp, (19<<2) + argp->count + 4);
resp->count = argp->count;
nfserr = nfsd_read(rqstp, fh_copy(&resp->fh, &argp->fh), NULL,