mirror of https://github.com/torvalds/linux.git
a3de58b12c
If all the subrequests in an unbuffered write stream fail, the subrequest
collector doesn't update the stream->transferred value and it retains its
initial LONG_MAX value. Unfortunately, if all active streams fail, then we
take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set
in wreq->transferred - which is then returned from ->write_iter().
LONG_MAX was chosen as the initial value so that all the streams can be
quickly assessed by taking the smallest value of all stream->transferred -
but this only works if we've set any of them.
Fix this by adding a flag to indicate whether the value in
stream->transferred is valid and checking that when we integrate the
values. stream->transferred can then be initialised to zero.
This was found by running the generic/750 xfstest against cifs with
cache=none. It splices data to the target file. Once (if) it has used up
all the available scratch space, the writes start failing with ENOSPC.
This causes ->write_iter() to fail. However, it was returning
wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought
the amount transferred was non-zero) and iter_file_splice_write() would
then try to clean up that amount of pipe bufferage - leading to an oops
when it overran. The kernel log showed:
CIFS: VFS: Send error in write = -28
followed by:
BUG: kernel NULL pointer dereference, address: 0000000000000008
with:
RIP: 0010:iter_file_splice_write+0x3a4/0x520
do_splice+0x197/0x4e0
or:
RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282)
iter_file_splice_write (fs/splice.c:755)
Also put a warning check into splice to announce if ->write_iter() returned
that it had written more than it was asked to.
Fixes:
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||
|---|---|---|
| .. | ||
| Kconfig | ||
| Makefile | ||
| buffered_read.c | ||
| buffered_write.c | ||
| direct_read.c | ||
| direct_write.c | ||
| fscache_cache.c | ||
| fscache_cookie.c | ||
| fscache_internal.h | ||
| fscache_io.c | ||
| fscache_main.c | ||
| fscache_proc.c | ||
| fscache_stats.c | ||
| fscache_volume.c | ||
| internal.h | ||
| iterator.c | ||
| locking.c | ||
| main.c | ||
| misc.c | ||
| objects.c | ||
| read_collect.c | ||
| read_pgpriv2.c | ||
| read_retry.c | ||
| read_single.c | ||
| rolling_buffer.c | ||
| stats.c | ||
| write_collect.c | ||
| write_issue.c | ||
| write_retry.c | ||