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>
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@ -290,6 +290,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp)
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RETURN_STATUS(nfserr_nametoolong);
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argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,
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page_address(rqstp->rq_arg.pages[0]),
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argp->tlen);
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if (IS_ERR(argp->tname))
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RETURN_STATUS(nfserrno(PTR_ERR(argp->tname)));
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@ -303,6 +304,7 @@ nfsd3_proc_symlink(struct svc_rqst *rqstp)
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fh_init(&resp->fh, NFS3_FHSIZE);
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nfserr = nfsd_symlink(rqstp, &resp->dirfh, argp->fname, argp->flen,
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argp->tname, &resp->fh);
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kfree(argp->tname);
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RETURN_STATUS(nfserr);
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}
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@ -454,6 +454,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp)
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return nfserr_nametoolong;
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argp->tname = svc_fill_symlink_pathname(rqstp, &argp->first,
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page_address(rqstp->rq_arg.pages[0]),
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argp->tlen);
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if (IS_ERR(argp->tname))
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return nfserrno(PTR_ERR(argp->tname));
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@ -466,6 +467,7 @@ nfsd_proc_symlink(struct svc_rqst *rqstp)
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nfserr = nfsd_symlink(rqstp, &argp->ffh, argp->fname, argp->flen,
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argp->tname, &newfh);
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kfree(argp->tname);
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fh_put(&argp->ffh);
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fh_put(&newfh);
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return nfserr;
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@ -499,7 +499,8 @@ unsigned int svc_fill_write_vector(struct svc_rqst *rqstp,
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struct page **pages,
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struct kvec *first, size_t total);
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char *svc_fill_symlink_pathname(struct svc_rqst *rqstp,
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struct kvec *first, size_t total);
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struct kvec *first, void *p,
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size_t total);
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#define RPC_MAX_ADDRBUFLEN (63U)
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@ -1577,65 +1577,48 @@ EXPORT_SYMBOL_GPL(svc_fill_write_vector);
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* svc_fill_symlink_pathname - Construct pathname argument for VFS symlink call
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* @rqstp: svc_rqst to operate on
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* @first: buffer containing first section of pathname
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* @p: buffer containing remaining section of pathname
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* @total: total length of the pathname argument
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*
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* Returns pointer to a NUL-terminated string, or an ERR_PTR. The buffer is
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* released automatically when @rqstp is recycled.
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* The VFS symlink API demands a NUL-terminated pathname in mapped memory.
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* Returns pointer to a NUL-terminated string, or an ERR_PTR. Caller must free
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* the returned string.
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*/
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char *svc_fill_symlink_pathname(struct svc_rqst *rqstp, struct kvec *first,
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size_t total)
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void *p, size_t total)
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{
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struct xdr_buf *arg = &rqstp->rq_arg;
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struct page **pages;
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char *result;
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size_t len, remaining;
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char *result, *dst;
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/* VFS API demands a NUL-terminated pathname. This function
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* uses a page from @rqstp as the pathname buffer, to enable
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* direct placement. Thus the total buffer size is PAGE_SIZE.
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* Space in this buffer for NUL-termination requires that we
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* cap the size of the returned symlink pathname just a
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* little early.
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*/
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if (total > PAGE_SIZE - 1)
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return ERR_PTR(-ENAMETOOLONG);
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result = kmalloc(total + 1, GFP_KERNEL);
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if (!result)
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return ERR_PTR(-ESERVERFAULT);
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/* Some types of transport can present the pathname entirely
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* in rq_arg.pages. If not, then copy the pathname into one
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* page.
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*/
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pages = arg->pages;
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WARN_ON_ONCE(arg->page_base != 0);
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if (first->iov_base == 0) {
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result = page_address(*pages);
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result[total] = '\0';
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} else {
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size_t len, remaining;
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char *dst;
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dst = result;
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remaining = total;
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result = page_address(*(rqstp->rq_next_page++));
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dst = result;
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remaining = total;
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len = min_t(size_t, total, first->iov_len);
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len = min_t(size_t, total, first->iov_len);
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if (len) {
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memcpy(dst, first->iov_base, len);
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dst += len;
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remaining -= len;
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/* No more than one page left */
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if (remaining) {
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len = min_t(size_t, remaining, PAGE_SIZE);
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memcpy(dst, page_address(*pages), len);
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dst += len;
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}
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*dst = '\0';
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}
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/* Sanity check: we don't allow the pathname argument to
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if (remaining) {
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len = min_t(size_t, remaining, PAGE_SIZE);
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memcpy(dst, p, len);
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dst += len;
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}
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*dst = '\0';
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/* Sanity check: Linux doesn't allow the pathname argument to
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* contain a NUL byte.
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*/
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if (strlen(result) != total)
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if (strlen(result) != total) {
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kfree(result);
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return ERR_PTR(-EINVAL);
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}
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return result;
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}
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EXPORT_SYMBOL_GPL(svc_fill_symlink_pathname);
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