staging: android: logger: Allow a UID to read it's own log entries
authorNick Kralevich <nnk@google.com>
Wed, 27 Feb 2013 06:07:37 +0000 (22:07 -0800)
committerKarol Lewandowski <k.lewandowsk@samsung.com>
Thu, 22 Apr 2021 09:02:48 +0000 (11:02 +0200)
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>
Signed-off-by: Nick Kralevich <nnk@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/android/logger.c
drivers/staging/android/logger.h

index dbc63cb..cfa6061 100644 (file)
@@ -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)
 {
index 9b929a8..cc6bbd9 100644 (file)
@@ -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
  * @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 */