Since commit cd678fce4280 ("switch logger to ->write_iter()"), any
attempt to write to the log results in the log data being written over
its own metadata, thus rendering the log unreadable.
The problem was first detected when I ran an Android userspace on the
v3.18-rc1 kernel. However the issue can also be observed with a
non-Android userspace by using echo/cat to write to/from /dev/log_main .
This patch resolves the problem by using a temporary to track the status
of not-yet-committed writes to the log buffer.
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
drivers/staging/android/logger.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c
index 28b93d3..a673ffa 100644
--- a/drivers/staging/android/logger.c
+++ b/drivers/staging/android/logger.c
@@ -420,7 +420,7 @@ static ssize_t logger_write_iter(struct kiocb *iocb, struct iov_iter *from)
struct logger_log *log = file_get_log(iocb->ki_filp);
struct logger_entry header;
struct timespec now;
- size_t len, count;
+ size_t len, count, w_off;
count = min_t(size_t, iocb->ki_nbytes, LOGGER_ENTRY_MAX_PAYLOAD);
@@ -452,11 +452,14 @@ static ssize_t logger_write_iter(struct kiocb *iocb, struct iov_iter *from)
memcpy(log->buffer + log->w_off, &header, len);
memcpy(log->buffer, (char *)&header + len, sizeof(header) - len);
- len = min(count, log->size - log->w_off);
+ /* Work with a copy until we are ready to commit the whole entry */
+ w_off = logger_offset(log, log->w_off + sizeof(struct logger_entry));
- if (copy_from_iter(log->buffer + log->w_off, len, from) != len) {
+ len = min(count, log->size - w_off);
+
+ if (copy_from_iter(log->buffer + w_off, len, from) != len) {
/*
- * Note that by not updating w_off, this abandons the
+ * Note that by not updating log->w_off, this abandons the
* portion of the new entry that *was* successfully
* copied, just above. This is intentional to avoid
* message corruption from missing fragments.
@@ -470,7 +473,7 @@ static ssize_t logger_write_iter(struct kiocb *iocb, struct iov_iter *from)
return -EFAULT;
}
- log->w_off = logger_offset(log, log->w_off + count);
+ log->w_off = logger_offset(log, w_off + count);
mutex_unlock(&log->mutex);
/* wake up any blocked readers */
--
1.9.3
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