android: logger: Allow a UID to read it's own log entries

Modify the kernel logger to record the UID associated with
the log entries. Always allow the same UID which generated a
log message to read the log message.

Allow anyone in the logs group, or anyone with CAP_SYSLOG, to
read all log entries.

In addition, allow the client to upgrade log formats, so they
can get additional information from the kernel.

Change-Id: Ie48fb614b43c9302a07ad2673b78dd8749b492b6
Signed-off-by: Nick Kralevich <nnk@google.com>

drivers/staging/android/logger.c

@@ -57,6 +57,8 @@ struct logger_reader {
 	struct logger_log	*log;	/* associated log */
 	struct list_head	list;	/* entry in logger_log's list */
 	size_t			r_off;	/* current read head offset */
+	bool			r_all;	/* reader can read all entries */
+	int			r_ver;	/* reader ABI version */
 };
 
 /* logger_offset - returns index 'n' into the log via (optimized) modulus */
@@ -86,25 +88,71 @@ static inline struct logger_log *file_get_log(struct file *file)
 }
 
 /*
- * get_entry_len - Grabs the length of the payload of the next entry starting
- * from 'off'.
+ * get_entry_header - returns a pointer to the logger_entry header within
+ * 'log' starting at offset 'off'. A temporary logger_entry 'scratch' must
+ * be provided. Typically the return value will be a pointer within
+ * 'logger->buf'.  However, a pointer to 'scratch' may be returned if
+ * the log entry spans the end and beginning of the circular buffer.
+ */
+static struct logger_entry *get_entry_header(struct logger_log *log,
+		size_t off, struct logger_entry *scratch)
+{
+	size_t len = min(sizeof(struct logger_entry), log->size - off);
+	if (len != sizeof(struct logger_entry)) {
+		memcpy(((void *) scratch), log->buffer + off, len);
+		memcpy(((void *) scratch) + len, log->buffer,
+			sizeof(struct logger_entry) - len);
+		return scratch;
+	}
+
+	return (struct logger_entry *) (log->buffer + off);
+}
+
+/*
+ * get_entry_msg_len - Grabs the length of the message of the entry
+ * starting from from 'off'.
  *
  * Caller needs to hold log->mutex.
  */
-static __u32 get_entry_len(struct logger_log *log, size_t off)
+static __u32 get_entry_msg_len(struct logger_log *log, size_t off)
 {
-	__u16 val;
+	struct logger_entry scratch;
+	struct logger_entry *entry;
 
-	switch (log->size - off) {
-	case 1:
-		memcpy(&val, log->buffer + off, 1);
-		memcpy(((char *) &val) + 1, log->buffer, 1);
-		break;
-	default:
-		memcpy(&val, log->buffer + off, 2);
+	entry = get_entry_header(log, off, &scratch);
+	return entry->len;
+}
+
+static size_t get_user_hdr_len(int ver)
+{
+	if (ver < 2)
+		return sizeof(struct user_logger_entry_compat);
+	else
+		return sizeof(struct logger_entry);
+}
+
+static ssize_t copy_header_to_user(int ver, struct logger_entry *entry,
+					 char __user *buf)
+{
+	void *hdr;
+	size_t hdr_len;
+	struct user_logger_entry_compat v1;
+
+	if (ver < 2) {
+		v1.len      = entry->len;
+		v1.__pad    = 0;
+		v1.pid      = entry->pid;
+		v1.tid      = entry->tid;
+		v1.sec      = entry->sec;
+		v1.nsec     = entry->nsec;
+		hdr         = &v1;
+		hdr_len     = sizeof(struct user_logger_entry_compat);
+	} else {
+		hdr         = entry;
+		hdr_len     = sizeof(struct logger_entry);
 	}
 
-	return sizeof(struct logger_entry) + val;
+	return copy_to_user(buf, hdr, hdr_len);
 }
 
 /*
@@ -118,15 +166,30 @@ static ssize_t do_read_log_to_user(struct logger_log *log,
 				   char __user *buf,
 				   size_t count)
 {
+	struct logger_entry scratch;
+	struct logger_entry *entry;
 	size_t len;
+	size_t msg_start;
 
 	/*
-	 * We read from the log in two disjoint operations. First, we read from
-	 * the current read head offset up to 'count' bytes or to the end of
+	 * First, copy the header to userspace, using the version of
+	 * the header requested
+	 */
+	entry = get_entry_header(log, reader->r_off, &scratch);
+	if (copy_header_to_user(reader->r_ver, entry, buf))
+		return -EFAULT;
+
+	count -= get_user_hdr_len(reader->r_ver);
+	buf += get_user_hdr_len(reader->r_ver);
+	msg_start = logger_offset(reader->r_off + sizeof(struct logger_entry));
+
+	/*
+	 * We read from the msg in two disjoint operations. First, we read from
+	 * the current msg head offset up to 'count' bytes or to the end of
 	 * the log, whichever comes first.
 	 */
-	len = min(count, log->size - reader->r_off);
-	if (copy_to_user(buf, log->buffer + reader->r_off, len))
+	len = min(count, log->size - msg_start);
+	if (copy_to_user(buf, log->buffer + msg_start, len))
 		return -EFAULT;
 
 	/*
@@ -137,9 +200,34 @@ static ssize_t do_read_log_to_user(struct logger_log *log,
 		if (copy_to_user(buf + len, log->buffer, count - len))
 			return -EFAULT;
 
-	reader->r_off = logger_offset(reader->r_off + count);
+	reader->r_off = logger_offset(reader->r_off +
+		sizeof(struct logger_entry) + count);
 
-	return count;
+	return count + get_user_hdr_len(reader->r_ver);
+}
+
+/*
+ * get_next_entry_by_uid - Starting at 'off', returns an offset into
+ * 'log->buffer' which contains the first entry readable by 'euid'
+ */
+static size_t get_next_entry_by_uid(struct logger_log *log,
+		size_t off, uid_t euid)
+{
+	while (off != log->w_off) {
+		struct logger_entry *entry;
+		struct logger_entry scratch;
+		size_t next_len;
+
+		entry = get_entry_header(log, off, &scratch);
+
+		if (entry->euid == euid)
+			return off;
+
+		next_len = sizeof(struct logger_entry) + entry->len;
+		off = logger_offset(off + next_len);
+	}
+
+	return off;
 }
 
 /*
@@ -151,7 +239,7 @@ static ssize_t do_read_log_to_user(struct logger_log *log,
  * 	- If there are no log entries to read, blocks until log is written to
  * 	- Atomically reads exactly one log entry
  *
- * Optimal read size is LOGGER_ENTRY_MAX_LEN. Will set errno to EINVAL if read
+ * Will set errno to EINVAL if read
  * buffer is insufficient to hold next entry.
  */
 static ssize_t logger_read(struct file *file, char __user *buf,
@@ -191,6 +279,10 @@ start:
 
 	mutex_lock(&log->mutex);
 
+	if (!reader->r_all)
+		reader->r_off = get_next_entry_by_uid(log,
+			reader->r_off, current_euid());
+
 	/* is there still something to read or did we race? */
 	if (unlikely(log->w_off == reader->r_off)) {
 		mutex_unlock(&log->mutex);
@@ -198,7 +290,8 @@ start:
 	}
 
 	/* get the size of the next entry */
-	ret = get_entry_len(log, reader->r_off);
+	ret = get_user_hdr_len(reader->r_ver) +
+		get_entry_msg_len(log, reader->r_off);
 	if (count < ret) {
 		ret = -EINVAL;
 		goto out;
@@ -224,7 +317,8 @@ static size_t get_next_entry(struct logger_log *log, size_t off, size_t len)
 	size_t count = 0;
 
 	do {
-		size_t nr = get_entry_len(log, off);
+		size_t nr = sizeof(struct logger_entry) +
+			get_entry_msg_len(log, off);
 		off = logger_offset(off + nr);
 		count += nr;
 	} while (count < len);
@@ -336,7 +430,9 @@ ssize_t logger_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	header.tid = current->pid;
 	header.sec = now.tv_sec;
 	header.nsec = now.tv_nsec;
+	header.euid = current_euid();
 	header.len = min_t(size_t, iocb->ki_left, LOGGER_ENTRY_MAX_PAYLOAD);
+	header.hdr_size = sizeof(struct logger_entry);
 
 	/* null writes succeed, return zero */
 	if (unlikely(!header.len))
@@ -409,6 +505,10 @@ static int logger_open(struct inode *inode, struct file *file)
 			return -ENOMEM;
 
 		reader->log = log;
+		reader->r_ver = 1;
+		reader->r_all = in_egroup_p(inode->i_gid) ||
+			capable(CAP_SYSLOG);
+
 		INIT_LIST_HEAD(&reader->list);
 
 		mutex_lock(&log->mutex);
@@ -463,6 +563,10 @@ static unsigned int logger_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &log->wq, wait);
 
 	mutex_lock(&log->mutex);
+	if (!reader->r_all)
+		reader->r_off = get_next_entry_by_uid(log,
+			reader->r_off, current_euid());
+
 	if (log->w_off != reader->r_off)
 		ret |= POLLIN | POLLRDNORM;
 	mutex_unlock(&log->mutex);
@@ -470,11 +574,25 @@ static unsigned int logger_poll(struct file *file, poll_table *wait)
 	return ret;
 }
 
+static long logger_set_version(struct logger_reader *reader, void __user *arg)
+{
+	int version;
+	if (copy_from_user(&version, arg, sizeof(int)))
+		return -EFAULT;
+
+	if ((version < 1) || (version > 2))
+		return -EINVAL;
+
+	reader->r_ver = version;
+	return 0;
+}
+
 static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct logger_log *log = file_get_log(file);
 	struct logger_reader *reader;
-	long ret = -ENOTTY;
+	long ret = -EINVAL;
+	void __user *argp = (void __user *) arg;
 
 	mutex_lock(&log->mutex);
 
@@ -499,8 +617,14 @@ static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			break;
 		}
 		reader = file->private_data;
+
+		if (!reader->r_all)
+			reader->r_off = get_next_entry_by_uid(log,
+				reader->r_off, current_euid());
+
 		if (log->w_off != reader->r_off)
-			ret = get_entry_len(log, reader->r_off);
+			ret = get_user_hdr_len(reader->r_ver) +
+				get_entry_msg_len(log, reader->r_off);
 		else
 			ret = 0;
 		break;
@@ -514,6 +638,22 @@ static long logger_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		log->head = log->w_off;
 		ret = 0;
 		break;
+	case LOGGER_GET_VERSION:
+		if (!(file->f_mode & FMODE_READ)) {
+			ret = -EBADF;
+			break;
+		}
+		reader = file->private_data;
+		ret = reader->r_ver;
+		break;
+	case LOGGER_SET_VERSION:
+		if (!(file->f_mode & FMODE_READ)) {
+			ret = -EBADF;
+			break;
+		}
+		reader = file->private_data;
+		ret = logger_set_version(reader, argp);
+		break;
 	}
 
 	mutex_unlock(&log->mutex);
@@ -534,8 +674,8 @@ static const struct file_operations logger_fops = {
 
 /*
  * Defines a log structure with name 'NAME' and a size of 'SIZE' bytes, which
- * must be a power of two, greater than LOGGER_ENTRY_MAX_LEN, and less than
- * LONG_MAX minus LOGGER_ENTRY_MAX_LEN.
+ * must be a power of two, and greater than
+ * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
  */
 #define DEFINE_LOGGER_DEVICE(VAR, NAME, SIZE) \
 static unsigned char _buf_ ## VAR[SIZE]; \

drivers/staging/android/logger.h

@@ -20,7 +20,12 @@
 #include <linux/types.h>
 #include <linux/ioctl.h>
 
-struct logger_entry {
+/*
+ * The userspace structure for version 1 of the logger_entry ABI.
+ * This structure is returned to userspace unless the caller requests
+ * an upgrade to a newer ABI version.
+ */
+struct user_logger_entry_compat {
 	__u16		len;	/* length of the payload */
 	__u16		__pad;	/* no matter what, we get 2 bytes of padding */
 	__s32		pid;	/* generating process's pid */
@@ -30,14 +35,28 @@ struct logger_entry {
 	char		msg[0];	/* the entry's payload */
 };
 
+/*
+ * The structure for version 2 of the logger_entry ABI.
+ * This structure is returned to userspace if ioctl(LOGGER_SET_VERSION)
+ * is called with version >= 2
+ */
+struct logger_entry {
+	__u16		len;		/* length of the payload */
+	__u16		hdr_size;	/* sizeof(struct logger_entry_v2) */
+	__s32		pid;		/* generating process's pid */
+	__s32		tid;		/* generating process's tid */
+	__s32		sec;		/* seconds since Epoch */
+	__s32		nsec;		/* nanoseconds */
+	uid_t		euid;		/* effective UID of logger */
+	char		msg[0];		/* the entry's payload */
+};
+
 #define LOGGER_LOG_RADIO	"log_radio"	/* radio-related messages */
 #define LOGGER_LOG_EVENTS	"log_events"	/* system/hardware events */
 #define LOGGER_LOG_SYSTEM	"log_system"	/* system/framework messages */
 #define LOGGER_LOG_MAIN		"log_main"	/* everything else */
 
-#define LOGGER_ENTRY_MAX_LEN		(4*1024)
-#define LOGGER_ENTRY_MAX_PAYLOAD	\
-	(LOGGER_ENTRY_MAX_LEN - sizeof(struct logger_entry))
+#define LOGGER_ENTRY_MAX_PAYLOAD	4076
 
 #define __LOGGERIO	0xAE
 
@@ -45,5 +64,7 @@ struct logger_entry {
 #define LOGGER_GET_LOG_LEN		_IO(__LOGGERIO, 2) /* used log len */
 #define LOGGER_GET_NEXT_ENTRY_LEN	_IO(__LOGGERIO, 3) /* next entry len */
 #define LOGGER_FLUSH_LOG		_IO(__LOGGERIO, 4) /* flush log */
+#define LOGGER_GET_VERSION		_IO(__LOGGERIO, 5) /* abi version */
+#define LOGGER_SET_VERSION		_IO(__LOGGERIO, 6) /* abi version */
 
 #endif /* _LINUX_LOGGER_H */