NFSD: Handle full-length symlinks

I've given up on the idea of zero-copy handling of SYMLINK on the
server side. This is because the Linux VFS symlink API requires the
symlink pathname to be in a NUL-terminated kmalloc'd buffer. The
NUL-termination is going to be problematic (watching out for
landing on a page boundary and dealing with a 4096-byte pathname).

I don't believe that SYMLINK creation is on a performance path or is
requested frequently enough that it will cause noticeable CPU cache
pollution due to data copies.

There will be two places where a transport callout will be necessary
to fill in the rqstp: one will be in the svc_fill_symlink_pathname()
helper that is used by NFSv2 and NFSv3, and the other will be in
nfsd4_decode_create().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Chuck Lever 2018-07-27 11:19:10 -04:00 committed by J. Bruce Fields
parent 3fd9557aec
commit 11b4d66ea3
4 changed files with 32 additions and 44 deletions

View File

@ -290,6 +290,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp)
RETURN_STATUS(nfserr_nametoolong);
argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,
page_address(rqstp->rq_arg.pages[0]),
argp->tlen);
if (IS_ERR(argp->tname))
RETURN_STATUS(nfserrno(PTR_ERR(argp->tname)));
@ -303,6 +304,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp)
fh_init(&resp->fh, NFS3_FHSIZE);
nfserr = nfsd_symlink(rqstp, &resp->dirfh, argp->fname, argp->flen,
argp->tname, &resp->fh);
kfree(argp->tname);
RETURN_STATUS(nfserr);
}

View File

@ -454,6 +454,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp)
return nfserr_nametoolong;
argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,
page_address(rqstp->rq_arg.pages[0]),
argp->tlen);
if (IS_ERR(argp->tname))
return nfserrno(PTR_ERR(argp->tname));
@ -466,6 +467,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp)
nfserr = nfsd_symlink(rqstp, &argp->ffh, argp->fname, argp->flen,
argp->tname, &newfh);
kfree(argp->tname);
fh_put(&argp->ffh);
fh_put(&newfh);
return nfserr;

View File

@ -499,7 +499,8 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp,
struct page **pages,
struct kvec *first, size_t total);
char *svc_fill_symlink_pathname(struct svc_rqst *rqstp,
struct kvec *first, size_t total);
struct kvec *first, void *p,
size_t total);
#define RPC_MAX_ADDRBUFLEN (63U)

View File

@ -1577,65 +1577,48 @@ EXPORT_SYMBOL_GPL(svc_fill_write_vector);
* svc_fill_symlink_pathname - Construct pathname argument for VFS symlink call
* @rqstp: svc_rqst to operate on
* @first: buffer containing first section of pathname
* @p: buffer containing remaining section of pathname
* @total: total length of the pathname argument
*
* Returns pointer to a NUL-terminated string, or an ERR_PTR. The buffer is
* released automatically when @rqstp is recycled.
* The VFS symlink API demands a NUL-terminated pathname in mapped memory.
* Returns pointer to a NUL-terminated string, or an ERR_PTR. Caller must free
* the returned string.
*/
char *svc_fill_symlink_pathname(struct svc_rqst *rqstp, struct kvec *first,
size_t total)
void *p, size_t total)
{
struct xdr_buf *arg = &rqstp->rq_arg;
struct page **pages;
char *result;
size_t len, remaining;
char *result, *dst;
/* VFS API demands a NUL-terminated pathname. This function
* uses a page from @rqstp as the pathname buffer, to enable
* direct placement. Thus the total buffer size is PAGE_SIZE.
* Space in this buffer for NUL-termination requires that we
* cap the size of the returned symlink pathname just a
* little early.
*/
if (total > PAGE_SIZE - 1)
return ERR_PTR(-ENAMETOOLONG);
result = kmalloc(total + 1, GFP_KERNEL);
if (!result)
return ERR_PTR(-ESERVERFAULT);
/* Some types of transport can present the pathname entirely
* in rq_arg.pages. If not, then copy the pathname into one
* page.
*/
pages = arg->pages;
WARN_ON_ONCE(arg->page_base != 0);
if (first->iov_base == 0) {
result = page_address(*pages);
result[total] = '\0';
} else {
size_t len, remaining;
char *dst;
dst = result;
remaining = total;
result = page_address(*(rqstp->rq_next_page++));
dst = result;
remaining = total;
len = min_t(size_t, total, first->iov_len);
len = min_t(size_t, total, first->iov_len);
if (len) {
memcpy(dst, first->iov_base, len);
dst += len;
remaining -= len;
/* No more than one page left */
if (remaining) {
len = min_t(size_t, remaining, PAGE_SIZE);
memcpy(dst, page_address(*pages), len);
dst += len;
}
*dst = '\0';
}
/* Sanity check: we don't allow the pathname argument to
if (remaining) {
len = min_t(size_t, remaining, PAGE_SIZE);
memcpy(dst, p, len);
dst += len;
}
*dst = '\0';
/* Sanity check: Linux doesn't allow the pathname argument to
* contain a NUL byte.
*/
if (strlen(result) != total)
if (strlen(result) != total) {
kfree(result);
return ERR_PTR(-EINVAL);
}
return result;
}
EXPORT_SYMBOL_GPL(svc_fill_symlink_pathname);