core(5): overwrite the oldest core dump

The '%I' format in the kern.corefile sysctl limits the number of
core files that a process can generate to the number stored in the
debug.ncores sysctl. The '%I' format is replaced by the single digit
index. Previously, if all indexes were taken the kernel would overwrite
only a core file with the highest index in a filename.
Currently the system will create a new core file if there is a free
index or if all slots are taken it will overwrite the oldest one.

Reviewed by:	kib(code), bcr (updating)
Differential Revision:	https://reviews.freebsd.org/D15991
Differential Revision:	https://reviews.freebsd.org/D16084

1 files changed, 104 insertions, 34 deletions

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 7a30869c7f24..04c35722b91f 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -3299,6 +3299,88 @@ SYSCTL_PROC(_kern, OID_AUTO, corefile, CTLTYPE_STRING | CTLFLAG_RW |
     CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A",
     "Process corefile name format string");
 
+static void
+vnode_close_locked(struct thread *td, struct vnode *vp)
+{
+
+	VOP_UNLOCK(vp, 0);
+	vn_close(vp, FWRITE, td->td_ucred, td);
+}
+
+/*
+ * If the core format has a %I in it, then we need to check
+ * for existing corefiles before defining a name.
+ * To do this we iterate over 0..num_cores to find a
+ * non-existing core file name to use. If all core files are
+ * already used we choose the oldest one.
+ */
+static int
+corefile_open_last(struct thread *td, char *name, int indexpos,
+    struct vnode **vpp)
+{
+	struct vnode *oldvp, *nextvp, *vp;
+	struct vattr vattr;
+	struct nameidata nd;
+	int error, i, flags, oflags, cmode;
+	struct timespec lasttime;
+
+	nextvp = oldvp = NULL;
+	cmode = S_IRUSR | S_IWUSR;
+	oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
+	    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
+
+	for (i = 0; i < num_cores; i++) {
+		flags = O_CREAT | FWRITE | O_NOFOLLOW;
+		name[indexpos] = '0' + i;
+
+		NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
+		error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred,
+		    NULL);
+		if (error != 0)
+			break;
+
+		vp = nd.ni_vp;
+		NDFREE(&nd, NDF_ONLY_PNBUF);
+		if ((flags & O_CREAT) == O_CREAT) {
+			nextvp = vp;
+			break;
+		}
+
+		error = VOP_GETATTR(vp, &vattr, td->td_ucred);
+		if (error != 0) {
+			vnode_close_locked(td, vp);
+			break;
+		}
+
+		if (oldvp == NULL ||
+		    lasttime.tv_sec > vattr.va_mtime.tv_sec ||
+		    (lasttime.tv_sec == vattr.va_mtime.tv_sec &&
+		    lasttime.tv_nsec >= vattr.va_mtime.tv_nsec)) {
+			if (oldvp != NULL)
+				vnode_close_locked(td, oldvp);
+			oldvp = vp;
+			lasttime = vattr.va_mtime;
+		} else {
+			vnode_close_locked(td, vp);
+		}
+	}
+
+	if (oldvp != NULL) {
+		if (nextvp == NULL)
+			nextvp = oldvp;
+		else
+			vnode_close_locked(td, oldvp);
+	}
+	if (error != 0) {
+		if (nextvp != NULL)
+			vnode_close_locked(td, oldvp);
+	} else {
+		*vpp = nextvp;
+	}
+
+	return (error);
+}
+
 /*
  * corefile_open(comm, uid, pid, td, compress, vpp, namep)
  * Expand the name described in corefilename, using name, uid, and pid
@@ -3315,11 +3397,11 @@ static int
 corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td,
     int compress, struct vnode **vpp, char **namep)
 {
-	struct nameidata nd;
 	struct sbuf sb;
+	struct nameidata nd;
 	const char *format;
 	char *hostname, *name;
-	int indexpos, i, error, cmode, flags, oflags;
+	int cmode, error, flags, i, indexpos, oflags;
 
 	hostname = NULL;
 	format = corefilename;
@@ -3385,48 +3467,36 @@ corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td,
 	sbuf_finish(&sb);
 	sbuf_delete(&sb);
 
-	cmode = S_IRUSR | S_IWUSR;
-	oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
-	    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
-
-	/*
-	 * If the core format has a %I in it, then we need to check
-	 * for existing corefiles before returning a name.
-	 * To do this we iterate over 0..num_cores to find a
-	 * non-existing core file name to use.
-	 */
 	if (indexpos != -1) {
-		for (i = 0; i < num_cores; i++) {
-			flags = O_CREAT | O_EXCL | FWRITE | O_NOFOLLOW;
-			name[indexpos] = '0' + i;
-			NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
-			error = vn_open_cred(&nd, &flags, cmode, oflags,
-			    td->td_ucred, NULL);
-			if (error) {
-				if (error == EEXIST)
-					continue;
-				log(LOG_ERR,
-				    "pid %d (%s), uid (%u):  Path `%s' failed "
-				    "on initial open test, error = %d\n",
-				    pid, comm, uid, name, error);
-			}
-			goto out;
+		error = corefile_open_last(td, name, indexpos, vpp);
+		if (error != 0) {
+			log(LOG_ERR,
+			    "pid %d (%s), uid (%u):  Path `%s' failed "
+			    "on initial open test, error = %d\n",
+			    pid, comm, uid, name, error);
+		}
+	} else {
+		cmode = S_IRUSR | S_IWUSR;
+		oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
+		    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
+		flags = O_CREAT | FWRITE | O_NOFOLLOW;
+
+		NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
+		error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred,
+		    NULL);
+		if (error == 0) {
+			*vpp = nd.ni_vp;
+			NDFREE(&nd, NDF_ONLY_PNBUF);
 		}
 	}
 
-	flags = O_CREAT | FWRITE | O_NOFOLLOW;
-	NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
-	error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred, NULL);
-out:
-	if (error) {
+	if (error != 0) {
 #ifdef AUDIT
 		audit_proc_coredump(td, name, error);
 #endif
 		free(name, M_TEMP);
 		return (error);
 	}
-	NDFREE(&nd, NDF_ONLY_PNBUF);
-	*vpp = nd.ni_vp;
 	*namep = name;
 	return (0);
 }