lib9p: Implemnt Topen, add permission checks in Twalk

6 files changed, 174 insertions, 63 deletions

diff --git a/lib9p/9p.c b/lib9p/9p.c
index 0e71071..b1d4c32 100644
--- a/lib9p/9p.c
+++ b/lib9p/9p.c
@@ -14,6 +14,8 @@
 #include "internal.h"
 
 int lib9p_error(struct lib9p_ctx *ctx, uint32_t linux_errno, char const *msg) {
+	if (lib9p_ctx_has_error(ctx))
+		return -1;
 	strncpy(ctx->err_msg, msg, sizeof(ctx->err_msg));
 	ctx->err_msg[sizeof(ctx->err_msg)-1] = '\0';
 	ctx->err_num = linux_errno;
@@ -24,6 +26,8 @@ int lib9p_errorf(struct lib9p_ctx *ctx, uint32_t linux_errno, char const *fmt, .
 	int n;
 	va_list args;
 
+	if (lib9p_ctx_has_error(ctx))
+		return -1;
 	va_start(args, fmt);
 	n = vsnprintf(ctx->err_msg, sizeof(ctx->err_msg), fmt, args);
 	va_end(args);
diff --git a/lib9p/idl/2002-9P2000.9p b/lib9p/idl/2002-9P2000.9p
index ba1382e..e45c0e1 100644
--- a/lib9p/idl/2002-9P2000.9p
+++ b/lib9p/idl/2002-9P2000.9p
@@ -53,7 +53,7 @@ bitfield dm = 4
 	"1=OTHER_W"
 	"0=OTHER_X"
 
-	"PERM=0777" # {OWNER,GROUP,OTHER}_{R,W,X}
+	"PERM_MASK=0777" # {OWNER,GROUP,OTHER}_{R,W,X}
 
 # QID Type - see `struct qid` below
 bitfield qt = 1
@@ -103,8 +103,8 @@ struct stat = "stat_size[2,val=end-&kern_type]"
 
 # "O"pen flags (flags to pass to Topen and Tcreate)
 bitfield o = 1
-	"0=rwx_0" # low bit of the 2-bit READ/WRITE/RDWR/EXEC enum
-	"1=rwx_1" # high bit of the 2-bit READ/WRITE/RDWR/EXEC enum"
+	"0=mode_0" # low bit of the 2-bit READ/WRITE/RDWR/EXEC enum
+	"1=mode_1" # high bit of the 2-bit READ/WRITE/RDWR/EXEC enum"
 	#"2=unused"
 	#"3=unused"
 	"4=TRUNC"
@@ -117,6 +117,9 @@ bitfield o = 1
 	"RDWR  = 2" # make available for this FID: Tread() and Twrite()
 	"EXEC  = 3" # make available for this FID: Tread()
 
+	"MODE_MASK = 0b00000011"
+	"FLAG_MASK = 0b11111100"
+
 msg Tversion = "size[4,val=end-&size] typ[1,val=100] tag[tag] max_msg_size[4] version[s]"
 msg Rversion = "size[4,val=end-&size] typ[1,val=101] tag[tag] max_msg_size[4] version[s]"
 msg Tauth    = "size[4,val=end-&size] typ[1,val=102] tag[tag] afid[fid] uname[s] aname[s]"
diff --git a/lib9p/include/lib9p/9p.generated.h b/lib9p/include/lib9p/9p.generated.h
index 6248ec7..584960c 100644
--- a/lib9p/include/lib9p/9p.generated.h
+++ b/lib9p/include/lib9p/9p.generated.h
@@ -80,7 +80,7 @@ typedef uint32_t lib9p_dm_t;
 #define   LIB9P_DM_OTHER_W       ((lib9p_dm_t)(1<<1))
 #define   LIB9P_DM_OTHER_X       ((lib9p_dm_t)(1<<0))
 
-#define   LIB9P_DM_PERM          ((lib9p_dm_t)(0777))
+#define   LIB9P_DM_PERM_MASK     ((lib9p_dm_t)(0777))
 
 typedef uint8_t lib9p_qt_t;
 
@@ -125,19 +125,21 @@ struct lib9p_stat {
 
 typedef uint8_t lib9p_o_t;
 
-/* unused                 ((lib9p_o_t)(1<<7)) */
-#define   LIB9P_O_RCLOSE  ((lib9p_o_t)(1<<6))
-/* unused                 ((lib9p_o_t)(1<<5)) */
-#define   LIB9P_O_TRUNC   ((lib9p_o_t)(1<<4))
-/* unused                 ((lib9p_o_t)(1<<3)) */
-/* unused                 ((lib9p_o_t)(1<<2)) */
-#define   LIB9P_O_rwx_1   ((lib9p_o_t)(1<<1))
-#define   LIB9P_O_rwx_0   ((lib9p_o_t)(1<<0))
-
-#define   LIB9P_O_READ    ((lib9p_o_t)(0))
-#define   LIB9P_O_WRITE   ((lib9p_o_t)(1))
-#define   LIB9P_O_RDWR    ((lib9p_o_t)(2))
-#define   LIB9P_O_EXEC    ((lib9p_o_t)(3))
+/* unused                    ((lib9p_o_t)(1<<7)) */
+#define   LIB9P_O_RCLOSE     ((lib9p_o_t)(1<<6))
+/* unused                    ((lib9p_o_t)(1<<5)) */
+#define   LIB9P_O_TRUNC      ((lib9p_o_t)(1<<4))
+/* unused                    ((lib9p_o_t)(1<<3)) */
+/* unused                    ((lib9p_o_t)(1<<2)) */
+#define   LIB9P_O_mode_1     ((lib9p_o_t)(1<<1))
+#define   LIB9P_O_mode_0     ((lib9p_o_t)(1<<0))
+
+#define   LIB9P_O_READ       ((lib9p_o_t)(0))
+#define   LIB9P_O_WRITE      ((lib9p_o_t)(1))
+#define   LIB9P_O_RDWR       ((lib9p_o_t)(2))
+#define   LIB9P_O_EXEC       ((lib9p_o_t)(3))
+#define   LIB9P_O_MODE_MASK  ((lib9p_o_t)(0b00000011))
+#define   LIB9P_O_FLAG_MASK  ((lib9p_o_t)(0b11111100))
 #endif /* defined(CONFIG_9P_ENABLE_9P2000) || defined(CONFIG_9P_ENABLE_9P2000_e) || defined(CONFIG_9P_ENABLE_9P2000_u) */
 
 /* messages *******************************************************************/
diff --git a/lib9p/include/lib9p/9p.h b/lib9p/include/lib9p/9p.h
index 3ad52f1..c3c6a8b 100644
--- a/lib9p/include/lib9p/9p.h
+++ b/lib9p/include/lib9p/9p.h
@@ -41,6 +41,12 @@ struct lib9p_ctx {
 	char                    err_msg[CONFIG_9P_MAX_ERR_SIZE];
 };
 
+static void lib9p_ctx_clear_error(struct lib9p_ctx *ctx) {
+	assert(ctx);
+	ctx->err_num = 0;
+	ctx->err_msg[0] = '\0';
+}
+
 static bool lib9p_ctx_has_error(struct lib9p_ctx *ctx) {
 	assert(ctx);
 	return ctx->err_num || ctx->err_msg[0];
diff --git a/lib9p/include/lib9p/srv.h b/lib9p/include/lib9p/srv.h
index d79e7db..5df6b1a 100644
--- a/lib9p/include/lib9p/srv.h
+++ b/lib9p/include/lib9p/srv.h
@@ -35,7 +35,6 @@ static inline int lib9p_srv_acknowledge_flush(struct lib9p_srv_ctx *ctx) {
 /* vtables you must implement *************************************************/
 
 struct lib9p_srv_file;
-struct lib9p_srv_io;
 
 struct lib9p_srv_file_vtable {
 	/* all - resource management */
@@ -43,28 +42,26 @@ struct lib9p_srv_file_vtable {
 	void                   (*free   )(struct lib9p_srv_ctx *, struct lib9p_srv_file *);
 
 	/* all - syscalls */
-	struct lib9p_srv_io   *(*io     )(struct lib9p_srv_ctx *, struct lib9p_srv_file *,
+	uint32_t               (*io     )(struct lib9p_srv_ctx *, struct lib9p_srv_file *,
 	                                  lib9p_o_t flags);
 	struct lib9p_stat      (*stat   )(struct lib9p_srv_ctx *, struct lib9p_srv_file *);
 	void                   (*wstat  )(struct lib9p_srv_ctx *, struct lib9p_srv_file *,
 	                                  struct lib9p_stat new);
 	void                   (*remove )(struct lib9p_srv_ctx *, struct lib9p_srv_file *);
 
-	/* directories */
+	/* directories - base */
 	struct lib9p_srv_file *(*dopen  )(struct lib9p_srv_ctx *, struct lib9p_srv_file *,
 	                                 char *childname);
 	struct lib9p_srv_file *(*dcreate)(struct lib9p_srv_ctx *, struct lib9p_srv_file *,
 	                                 char *childname,
 	                                 lib9p_dm_t perm, lib9p_o_t flags);
-};
 
-struct lib9p_srv_io_dir_vtable {
+	/* directories - once opened */
 	size_t                 (*readdir)(struct lib9p_srv_ctx *, struct lib9p_srv_io_dir *,
 	                                  struct lib9p_stat *buf, size_t count,
 	                                  size_t offset);
-};
 
-struct lib9p_srv_io_file_vtable {
+	/* non-directories - once opened */
 	uint32_t               (*pread  )(struct lib9p_srv_ctx *, struct lib9p_srv_io_file *,
 	                                  void *buf, uint32_t count,
 	                                  uint64_t offset);
@@ -78,25 +75,19 @@ struct lib9p_srv_io_file_vtable {
 struct lib9p_srv_file {
 	struct lib9p_srv_file_vtable    *vtable;
 
-	/* Managed by srv.c */
-	struct lib9p_srv_file           *_parent_dir;
-
-	/* This is where your implementation data goes.  */
-	char                             data[0];
-};
-
-struct lib9p_srv_io {
-	union {
-		struct lib9p_srv_io_dir_vtable   *dir;
-		struct lib9p_srv_io_file_vtable  *file;
-	}                        vtable;
+	/* Managed by srv.c, but should be cloned by ->vtable->clone().  */
+	struct lib9p_srv_file           *_parent_dir; /* clone this
 
-	struct lib9p_srv_file   *file;
-	struct lib9p_qid         qid;
-	uint32_t                 iounit;
+	/* Managed by srv.c, and should be initialized to 0 by ->vtable->clone().  */
+	/* ref type 1: an entry in fidmap
+	 * ref type 2: ->_parent_dir of another file */
+	struct lib9p_srv_file           *_refcount;
+	lib9p_o_t                        _io_flags;
+	struct lib9p_qid                 _io_qid;
+	uint32_t                         _io_unit;
 
 	/* This is where your implementation data goes.  */
-	char                     data[0];
+	char                             data[0];
 };
 
 /* main server entrypoints ****************************************************/
diff --git a/lib9p/srv.c b/lib9p/srv.c
index 9d1b4ed..8940afe 100644
--- a/lib9p/srv.c
+++ b/lib9p/srv.c
@@ -365,12 +365,39 @@ static void handle_message(struct _lib9p_srv_req *ctx) {
 	}
 }
 
+#define handler_common(ctx, req, resp) do { \
+		assert(ctx);                \
+		assert(req);                \
+		assert(resp);               \
+		resp->tag = req->tag;       \
+	} while (0)
+
+static inline bool check_perm(struct lib9p_srv_ctx *ctx, struct lib9p_stat *stat, uint8_t action) {
+	assert(ctx);
+	assert(stat);
+	assert(action);
+
+	/* TODO actually check user and group instead of just assuming "other".  */
+	uint8_t mode = (uint8_t)(stat->file_mode & 07);
+
+	return mode & action;
+}
+
+static inline bool release(struct lib9p_srv_ctx *ctx, struct lib9p_srv_file *file) {
+	assert(file);
+	file->_refcount--;
+	if (file->_refcount == 0) {
+		if (file->_parent_dir != file)
+			release(ctx, file->_parent_dir);
+		file->vtable->free(ctx, file);
+	}
+	return lib9p_ctx_has_error(&ctx->basectx);
+}
+
 static void handle_Tversion(struct _lib9p_srv_req *ctx,
                             struct lib9p_msg_Tversion *req,
                             struct lib9p_msg_Rversion *resp) {
-	assert(ctx);
-	assert(req);
-	assert(resp);
+	handler_common(ctx, req, resp);
 
 	enum lib9p_version version = LIB9P_VER_unknown;
 
@@ -440,13 +467,6 @@ static void handle_Tversion(struct _lib9p_srv_req *ctx,
 	ctx->parent_sess->rerror_overhead = min_msg_size;
 }
 
-#define handler_common(ctx, req, resp) do { \
-		assert(ctx);                \
-		assert(req);                \
-		assert(resp);               \
-		resp->tag = req->tag;       \
-	} while (0)
-
 static void handle_Tauth(struct _lib9p_srv_req *ctx,
                          struct lib9p_msg_Tauth *req,
                          struct lib9p_msg_Rauth *resp) {
@@ -522,11 +542,12 @@ static void handle_Tattach(struct _lib9p_srv_req *ctx,
 	if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 		return;
 	rootdir->_parent_dir = rootdir;
+	rootdir->_refcount++;
 
 	if (!fidmap_store(&ctx->parent_sess->fids, req->fid, rootdir)) {
 		lib9p_error(&ctx->ctx.basectx,
 		            LINUX_EMFILE, "too many open files");
-		rootdir->vtable->free(&ctx->ctx, rootdir);
+		release(&ctx->ctx, rootdir);
 		return;
 	}
 
@@ -546,7 +567,7 @@ static void handle_Tattach(struct _lib9p_srv_req *ctx,
 static void handle_Tflush(struct _lib9p_srv_req *ctx,
                           struct lib9p_msg_Tflush *req,
                           struct lib9p_msg_Rflush *resp) {
-	handler_common(ctx, req, resp);;
+	handler_common(ctx, req, resp);
 
 	lib9p_error(&ctx->ctx.basectx,
 	            LINUX_EOPNOTSUPP, "flush not yet implemented");
@@ -577,6 +598,7 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 		assert((dirp == NULL) == lib9p_ctx_has_error(&ctx->ctx.basectx));
 		if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 			return;
+		dirp->_refcount++; /* ref-A: presumptive insertion into fidmap */
 	}
 
 	resp->wqid = (struct lib9p_qid *)(&resp[1]);
@@ -588,7 +610,9 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 			struct lib9p_stat stat = dirp->vtable->stat(&ctx->ctx, dirp);
 			if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 				break;
-			if (!(stat.file_qid.type & LIB9P_QT_DIR) || !(stat.file_mode & LIB9P_DM_DIR)) {
+			assert( ((bool)(stat.file_qid.type & LIB9P_QT_DIR)) ==
+			        ((bool)(stat.file_mode & LIB9P_DM_DIR)) );
+			if (!(stat.file_mode & LIB9P_DM_DIR)) {
 				lib9p_error(&ctx->ctx.basectx,
 				            LINUX_ENOTDIR, "not a directory");
 				break;
@@ -598,14 +622,27 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 			assert((memberp == NULL) == lib9p_ctx_has_error(&ctx->ctx.basectx));
 			if (lib9p_ctx_has_error(&ctx->ctx.basectx))
 				break;
+			memberp->_parent_dir = dirp;
+			dirp->_refcount++; /* memberp->_parent_dir */
 		}
+		memberp->_refcount++; /* presumptively take ref-A */
 
 		struct lib9p_stat stat = memberp->vtable->stat(&ctx->ctx, memberp);
-		if (lib9p_ctx_has_error(&ctx->ctx.basectx))
+		if (lib9p_ctx_has_error(&ctx->ctx.basectx)) {
+			release(&ctx->ctx, memberp); /* presumption of taking ref-A failed */
+			break;
+		}
+		if (!check_perm(&ctx->ctx, &stat, 0b001)) {
+			lib9p_error(&ctx->ctx.basectx,
+			            LINUX_EACCES, "you do not have execute permission on that directory");
+			release(&ctx->ctx, memberp); /* presumption of taking ref-A failed */
 			break;
+		}
+
 		resp->wqid[resp->nwqid] = stat.file_qid;
 
-		dirp->vtable->free(&ctx->ctx, dirp);
+		/* presumption of taking ref-A succeeded */
+		release(&ctx->ctx, dirp);
 		dirp = memberp;
 	}
 	if (resp->nwqid == req->nwname) {
@@ -615,21 +652,89 @@ static void handle_Twalk(struct _lib9p_srv_req *ctx,
 			if (!fidmap_store(&ctx->parent_sess->fids, req->newfid, dirp)) {
 				lib9p_error(&ctx->ctx.basectx,
 				            LINUX_EMFILE, "too many open files");
-				dirp->vtable->free(&ctx->ctx, dirp);
+				release(&ctx->ctx, dirp); /* presumption of insertion failed */
 			}
-	} else if (resp->nwqid > 0) {
-		ctx->ctx.basectx.err_num = 0;
-		ctx->ctx.basectx.err_msg[0] = '\0';
+	} else {
+		assert(lib9p_ctx_has_error(&ctx->ctx.basectx));
+		if (req->newfid != req->fid)
+			release(&ctx->ctx, dirp); /* presumption of insertion failed */
+		if (resp->nwqid > 0)
+			lib9p_ctx_clear_error(&ctx->ctx.basectx);
 	}
 }
 
 static void handle_Topen(struct _lib9p_srv_req *ctx,
                          struct lib9p_msg_Topen *req,
                          struct lib9p_msg_Ropen *resp) {
-	handler_common(ctx, req, resp);;
+	handler_common(ctx, req, resp);
 
-	lib9p_error(&ctx->ctx.basectx,
-	            LINUX_EOPNOTSUPP, "open not yet implemented");
+	struct lib9p_srv_file **filepp = fidmap_load(&ctx->parent_sess->fids, req->fid);
+	if (!filepp) {
+		lib9p_errorf(&ctx->ctx.basectx,
+		             LINUX_EBADF, "bad file number %"PRIu32, req->fid);
+		return;
+	}
+	struct lib9p_srv_file *filep = *filepp;
+
+	struct lib9p_stat stat = filep->vtable->stat(&ctx->ctx, filep);
+	if (lib9p_ctx_has_error(&ctx->ctx.basectx))
+		return;
+	assert( ((bool)(stat.file_qid.type & LIB9P_QT_DIR)) ==
+	        ((bool)(stat.file_mode & LIB9P_DM_DIR)) );
+
+	lib9p_o_t flags = req->mode;
+	if (stat.file_mode & LIB9P_DM_DIR) {
+		if ( ((flags & LIB9P_O_MODE_MASK) != LIB9P_O_READ) ||
+		     (flags & LIB9P_O_TRUNC) ||
+		     (flags & LIB9P_O_RCLOSE) ) {
+			lib9p_error(&ctx->ctx.basectx,
+			            LINUX_EISDIR, "directories cannot be written, executed, truncated, or removed-on-close");
+			return;
+		}
+	} else {
+		if (stat.file_mode & LIB9P_QT_APPEND)
+			flags = flags & ~LIB9P_O_TRUNC;
+	}
+	if (flags & LIB9P_O_RCLOSE) {
+		struct lib9p_stat parent_stat = filep->_parent_dir->vtable->stat(&ctx->ctx, filep->_parent_dir);
+		if (lib9p_ctx_has_error(&ctx->ctx.basectx))
+			return;
+		if (!check_perm(&ctx->ctx, &parent_stat, 0b010)) {
+			lib9p_error(&ctx->ctx.basectx,
+			            LINUX_EACCES, "permission denied to remove-on-close");
+			return;
+		}
+	}
+	uint8_t perm_bits = 0;
+	switch (flags & LIB9P_O_MODE_MASK) {
+	case LIB9P_O_READ:
+		perm_bits = 0b100;
+		break;
+	case LIB9P_O_WRITE:
+		perm_bits = 0b010;
+		break;
+	case LIB9P_O_RDWR:
+		perm_bits = 0b110;
+		break;
+	case LIB9P_O_EXEC:
+		perm_bits = 0b001;
+		break;
+	}
+	if (!check_perm(&ctx->ctx, &stat, perm_bits)) {
+		lib9p_error(&ctx->ctx.basectx,
+		            LINUX_EACCES, "permission denied");
+	}
+
+	uint32_t iounit = filep->vtable->io(&ctx->ctx, filep, flags);
+	if (lib9p_ctx_has_error(&ctx->ctx.basectx))
+		return;
+
+	filep->_io_flags = flags;
+	filep->_io_unit = iounit;
+	filep->_io_qid = stat.file_qid;
+
+	resp->qid = filep->_io_qid;
+	resp->iounit = filep->_io_unit;
 }
 
 static void handle_Tcreate(struct _lib9p_srv_req *ctx,
@@ -702,7 +807,7 @@ static void handle_Tstat(struct _lib9p_srv_req *ctx,
 static void handle_Twstat(struct _lib9p_srv_req *ctx,
                           struct lib9p_msg_Twstat *req,
                           struct lib9p_msg_Rwstat *resp) {
-	handler_common(ctx, req, resp);;
+	handler_common(ctx, req, resp);
 
 	lib9p_error(&ctx->ctx.basectx,
 	            LINUX_EOPNOTSUPP, "wstat not yet implemented");