[PATCH 4/5] staging: android: logger: Allow a UID to read it's own log entries

John Stultz
2013-02-27T06:09:18Z

From: Nick Kralevich <nnk@google.com>

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.

Cc: Android Kernel Team <kernel-team@android.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Nick Kralevich <nnk@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/staging/android/logger.c | 191 +++++++++++++++++++++++++++++++++-----
drivers/staging/android/logger.h | 40 +++++++-
2 files changed, 202 insertions(+), 29 deletions(-)

diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c
index dbc63cb..cfa6061 100644
--- a/drivers/staging/android/logger.c
+++ b/drivers/staging/android/logger.c
@@ -68,6 +68,8 @@ static LIST_HEAD(log_list);
* @log: The associated log
* @list: The associated entry in @logger_log's list
* @r_off: The current read head offset.
+ * @r_all: Reader can read all entries
+ * @r_ver: Reader ABI version
*
* This object lives from open to release, so we don't need additional
* reference counting. The structure is protected by log->mutex.
@@ -76,6 +78,8 @@ struct logger_reader {
struct logger_log *log;
struct list_head list;
size_t r_off;
+ bool r_all;
+ int r_ver;
};

/* logger_offset - returns index 'n' into the log via (optimized) modulus */
@@ -109,8 +113,29 @@ 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'.
*
* An entry length is 2 bytes (16 bits) in host endian order.
* In the log, the length does not include the size of the log entry structure.
@@ -118,20 +143,45 @@ static inline struct logger_log *file_get_log(struct file *file)
*
* 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;

- /* copy 2 bytes from buffer, in memcpy order, */
- /* handling possible wrap at end of buffer */
+ entry = get_entry_header(log, off, &scratch);
+ return entry->len;
+}

- ((__u8 *)&val)[0] = log->buffer[off];
- if (likely(off+1 < log->size))
- ((__u8 *)&val)[1] = log->buffer[off+1];
+static size_t get_user_hdr_len(int ver)
+{
+ if (ver < 2)
+ return sizeof(struct user_logger_entry_compat);
else
- ((__u8 *)&val)[1] = log->buffer[0];
+ 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);
}

/*
@@ -145,15 +195,31 @@ 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(log,
+ 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;

/*
@@ -164,9 +230,34 @@ 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(log, reader->r_off + count);
+ reader->r_off = logger_offset(log, 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(log, off + next_len);
+ }
+
+ return off;
}

/*
@@ -178,7 +269,7 @@ 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,
@@ -219,6 +310,10 @@ 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);
@@ -226,7 +321,8 @@ 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;
@@ -252,7 +348,8 @@ 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(log, off + nr);
count += nr;
} while (count < len);
@@ -382,7 +479,9 @@ static 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))
@@ -463,6 +562,10 @@ 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);
@@ -522,6 +625,10 @@ 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);
@@ -529,11 +636,25 @@ 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);

@@ -558,8 +679,14 @@ 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;
@@ -573,6 +700,22 @@ 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);
@@ -592,8 +735,8 @@ static const struct file_operations logger_fops = {
};

/*
- * Log size must be a power of two, greater than LOGGER_ENTRY_MAX_LEN,
- * and less than LONG_MAX minus LOGGER_ENTRY_MAX_LEN.
+ * Log size must must be a power of two, and greater than
+ * (LOGGER_ENTRY_MAX_PAYLOAD + sizeof(struct logger_entry)).
*/
static int __init create_log(char *log_name, int size)
{
diff --git a/drivers/staging/android/logger.h b/drivers/staging/android/logger.h
index 9b929a8..cc6bbd9 100644
--- a/drivers/staging/android/logger.h
+++ b/drivers/staging/android/logger.h
@@ -21,7 +21,7 @@
#include <linux/ioctl.h>

/**
- * struct logger_entry - defines a single entry that is given to a logger
+ * struct user_logger_entry_compat - defines a single entry that is given to a logger
* @len: The length of the payload
* @__pad: Two bytes of padding that appear to be required
* @pid: The generating process' process ID
@@ -29,8 +29,12 @@
* @sec: The number of seconds that have elapsed since the Epoch
* @nsec: The number of nanoseconds that have elapsed since @sec
* @msg: The message that is to be logged
+ *
+ * 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 logger_entry {
+struct user_logger_entry_compat {
__u16 len;
__u16 __pad;
__s32 pid;
@@ -40,14 +44,38 @@ struct logger_entry {
char msg[0];
};

+/**
+ * struct logger_entry - defines a single entry that is given to a logger
+ * @len: The length of the payload
+ * @hdr_size: sizeof(struct logger_entry_v2)
+ * @pid: The generating process' process ID
+ * @tid: The generating process' thread ID
+ * @sec: The number of seconds that have elapsed since the Epoch
+ * @nsec: The number of nanoseconds that have elapsed since @sec
+ * @euid: Effective UID of logger
+ * @msg: The message that is to be logged
+ *
+ * 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;
+ __u16 hdr_size;
+ __s32 pid;
+ __s32 tid;
+ __s32 sec;
+ __s32 nsec;
+ uid_t euid;
+ char msg[0];
+};
+
#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

@@ -55,5 +83,7 @@ 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 */
--
1.7.10.4