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| author |   Daniel Thompson <daniel.thompson@linaro.org> | 2014-10-27 18:51:43 +0000 |
|---|---|---|
| committer |   Al Viro <viro@zeniv.linux.org.uk> | 2014-10-28 18:24:30 -0400 |
| commit | 5fecf3a1e1a0af61eb34eb6976ec9f59cca65d3f (patch) | |
| tree | 3ce7295f4f7429418339fe3d47c4c996dafbbc8d | |
| parent | Linux 3.18-rc2 (diff) | |
| download | linux-dev-5fecf3a1e1a0af61eb34eb6976ec9f59cca65d3f.tar.xz linux-dev-5fecf3a1e1a0af61eb34eb6976ec9f59cca65d3f.zip | |
staging: android: logger: Fix log corruption regression
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@linaro.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| -rw-r--r-- | drivers/staging/android/logger.c | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c index 28b93d39a94e..a673ffa34aa3 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 */ |