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staging: android: logger: Fix log corruption regression 

Since commit cd678fce42 ("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@linaro.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Daniel Thompson 2014-10-27 18:51:43 +00:00 committed by Al Viro
parent cac7f24298
commit 5fecf3a1e1
1 changed files with 8 additions and 5 deletions
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13
drivers/staging/android/logger.c
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@ -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 */