The sendfile(2) allows to send extra data from userspace before the file

data (headers).  Historically the size of the headers was not checked
against the socket buffer space.  Application could easily overcommit the
socket buffer space.

With the new sendfile (r293439) the problem remained, but a KASSERT was
inserted that checked that amount of data written to the socket matches
its space.  In case when size of headers is bigger that socket space,
KASSERT fires.  Without INVARIANTS the new sendfile won't panic, but
would report incorrect amount of bytes sent.

o With this change, the headers copyin is moved down into the cycle, after
  the sbspace() check.  The uio size is trimmed by socket space there,
  which fixes the overcommit problem and its consequences.
o The compatibility handling for FreeBSD 4 sendfile headers API is pushed
  up the stack to syscall wrappers.  This required a copy and paste of the
  code, but in turn this allowed to remove extra stack carried parameter
  from fo_sendfile_t, and embrace entire compat code into #ifdef.  If in
  future we got more fo_sendfile_t function, the copy and paste level would
  even reduce.

Reviewed by:	emax, gallatin, Maxim Dounin <mdounin mdounin.ru>
Tested by:	Vitalij Satanivskij <satan ukr.net>
Sponsored by:	Netflix

5 files changed, 48 insertions, 34 deletions

diff --git a/sys/compat/freebsd32/freebsd32_misc.c b/sys/compat/freebsd32/freebsd32_misc.c
index bdcdf6f..598bdc5 100644
--- a/sys/compat/freebsd32/freebsd32_misc.c
+++ b/sys/compat/freebsd32/freebsd32_misc.c
@@ -1653,6 +1653,19 @@ freebsd32_do_sendfile(struct thread *td,
 			    hdtr32.hdr_cnt, &hdr_uio);
 			if (error)
 				goto out;
+#ifdef COMPAT_FREEBSD4
+			/*
+			 * In FreeBSD < 5.0 the nbytes to send also included
+			 * the header.  If compat is specified subtract the
+			 * header size from nbytes.
+			 */
+			if (compat) {
+				if (uap->nbytes > hdr_uio->uio_resid)
+					uap->nbytes -= hdr_uio->uio_resid;
+				else
+					uap->nbytes = 0;
+			}
+#endif
 		}
 		if (hdtr.trailers != NULL) {
 			iov32 = PTRIN(hdtr32.trailers);
@@ -1670,7 +1683,7 @@ freebsd32_do_sendfile(struct thread *td,
 		goto out;
 
 	error = fo_sendfile(fp, uap->s, hdr_uio, trl_uio, offset,
-	    uap->nbytes, &sbytes, uap->flags, compat ? SFK_COMPAT : 0, td);
+	    uap->nbytes, &sbytes, uap->flags, td);
 	fdrop(fp, td);
 
 	if (uap->sbytes != NULL)
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 00bd54b..b37adcc 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -3958,7 +3958,7 @@ badfo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
 static int
 badfo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
     struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
-    int kflags, struct thread *td)
+    struct thread *td)
 {
 
 	return (EBADF);
@@ -4044,7 +4044,7 @@ invfo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
 int
 invfo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
     struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
-    int kflags, struct thread *td)
+    struct thread *td)
 {
 
 	return (EINVAL);
diff --git a/sys/kern/kern_sendfile.c b/sys/kern/kern_sendfile.c
index a2e1311..7ee7780 100644
--- a/sys/kern/kern_sendfile.c
+++ b/sys/kern/kern_sendfile.c
@@ -516,7 +516,7 @@ sendfile_getsock(struct thread *td, int s, struct file **sock_fp,
 int
 vn_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
     struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
-    int kflags, struct thread *td)
+    struct thread *td)
 {
 	struct file *sock_fp;
 	struct vnode *vp;
@@ -534,7 +534,7 @@ vn_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
 	so = NULL;
 	m = mh = NULL;
 	sfs = NULL;
-	sbytes = 0;
+	hdrlen = sbytes = 0;
 	softerr = 0;
 
 	error = sendfile_getobj(td, fp, &obj, &vp, &shmfd, &obj_size, &bsize);
@@ -560,26 +560,6 @@ vn_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
 		cv_init(&sfs->cv, "sendfile");
 	}
 
-	/* If headers are specified copy them into mbufs. */
-	if (hdr_uio != NULL && hdr_uio->uio_resid > 0) {
-		hdr_uio->uio_td = td;
-		hdr_uio->uio_rw = UIO_WRITE;
-		/*
-		 * In FBSD < 5.0 the nbytes to send also included
-		 * the header.  If compat is specified subtract the
-		 * header size from nbytes.
-		 */
-		if (kflags & SFK_COMPAT) {
-			if (nbytes > hdr_uio->uio_resid)
-				nbytes -= hdr_uio->uio_resid;
-			else
-				nbytes = 0;
-		}
-		mh = m_uiotombuf(hdr_uio, M_WAITOK, 0, 0, 0);
-		hdrlen = m_length(mh, &mhtail);
-	} else
-		hdrlen = 0;
-
 	rem = nbytes ? omin(nbytes, obj_size - offset) : obj_size - offset;
 
 	/*
@@ -668,11 +648,20 @@ retry_space:
 		SOCKBUF_UNLOCK(&so->so_snd);
 
 		/*
-		 * Reduce space in the socket buffer by the size of
-		 * the header mbuf chain.
-		 * hdrlen is set to 0 after the first loop.
+		 * At the beginning of the first loop check if any headers
+		 * are specified and copy them into mbufs.  Reduce space in
+		 * the socket buffer by the size of the header mbuf chain.
+		 * Clear hdr_uio here and hdrlen at the end of the first loop.
 		 */
-		space -= hdrlen;
+		if (hdr_uio != NULL && hdr_uio->uio_resid > 0) {
+			hdr_uio->uio_td = td;
+			hdr_uio->uio_rw = UIO_WRITE;
+			hdr_uio->uio_resid = min(hdr_uio->uio_resid, space);
+			mh = m_uiotombuf(hdr_uio, M_WAITOK, 0, 0, 0);
+			hdrlen = m_length(mh, &mhtail);
+			space -= hdrlen;
+			hdr_uio = NULL;
+		}
 
 		if (vp != NULL) {
 			error = vn_lock(vp, LK_SHARED);
@@ -944,6 +933,19 @@ sendfile(struct thread *td, struct sendfile_args *uap, int compat)
 			    &hdr_uio);
 			if (error != 0)
 				goto out;
+#ifdef COMPAT_FREEBSD4
+			/*
+			 * In FreeBSD < 5.0 the nbytes to send also included
+			 * the header.  If compat is specified subtract the
+			 * header size from nbytes.
+			 */
+			if (compat) {
+				if (uap->nbytes > hdr_uio->uio_resid)
+					uap->nbytes -= hdr_uio->uio_resid;
+				else
+					uap->nbytes = 0;
+			}
+#endif
 		}
 		if (hdtr.trailers != NULL) {
 			error = copyinuio(hdtr.trailers, hdtr.trl_cnt,
@@ -965,7 +967,7 @@ sendfile(struct thread *td, struct sendfile_args *uap, int compat)
 	}
 
 	error = fo_sendfile(fp, uap->s, hdr_uio, trl_uio, uap->offset,
-	    uap->nbytes, &sbytes, uap->flags, compat ? SFK_COMPAT : 0, td);
+	    uap->nbytes, &sbytes, uap->flags, td);
 	fdrop(fp, td);
 
 	if (uap->sbytes != NULL)
diff --git a/sys/sys/file.h b/sys/sys/file.h
index 524c1ce..c30eb05 100644
--- a/sys/sys/file.h
+++ b/sys/sys/file.h
@@ -112,7 +112,7 @@ typedef	int fo_chown_t(struct file *fp, uid_t uid, gid_t gid,
 		    struct ucred *active_cred, struct thread *td);
 typedef int fo_sendfile_t(struct file *fp, int sockfd, struct uio *hdr_uio,
 		    struct uio *trl_uio, off_t offset, size_t nbytes,
-		    off_t *sent, int flags, int kflags, struct thread *td);
+		    off_t *sent, int flags, struct thread *td);
 typedef int fo_seek_t(struct file *fp, off_t offset, int whence,
 		    struct thread *td);
 typedef int fo_fill_kinfo_t(struct file *fp, struct kinfo_file *kif,
@@ -376,11 +376,11 @@ fo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
 static __inline int
 fo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
     struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
-    int kflags, struct thread *td)
+    struct thread *td)
 {
 
 	return ((*fp->f_ops->fo_sendfile)(fp, sockfd, hdr_uio, trl_uio, offset,
-	    nbytes, sent, flags, kflags, td));
+	    nbytes, sent, flags, td));
 }
 
 static __inline int
diff --git a/sys/sys/socket.h b/sys/sys/socket.h
index c20b075..649ba00 100644
--- a/sys/sys/socket.h
+++ b/sys/sys/socket.h
@@ -594,7 +594,6 @@ struct sf_hdtr {
 #define	SF_FLAGS(rh, flags)	(((rh) << 16) | (flags))
 
 #ifdef _KERNEL
-#define	SFK_COMPAT	0x00000001
 #define	SF_READAHEAD(flags)	((flags) >> 16)
 #endif /* _KERNEL */