I got a report about unkillable task eating CPU. Further
investigation shows, that the problem is in the fuse_fill_write_pages()
function. If iov's first segment has zero length, we get an infinite
loop, because we never reach iov_iter_advance() call.
Fix this by calling iov_iter_advance() before repeating an attempt to
copy data from userspace.
A similar problem is described in 124d3b7041f ("fix writev regression:
pan hanging unkillable and un-straceable"). If zero-length segmend
is followed by segment with invalid address,
iov_iter_fault_in_readable() checks only first segment (zero-length),
iov_iter_copy_from_user_atomic() skips it, fails at second and
returns zero -> goto again without skipping zero-length segment.
Patch calls iov_iter_advance() before goto again: we'll skip zero-length
segment at second iteraction and iov_iter_fault_in_readable() will detect
invalid address.
Special thanks to Konstantin Khlebnikov, who helped a lot with the commit
description.
Signed-off-by: Roman Gushchin <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Maxim Patlasov <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Roman Gushchin <[email protected]>
---
fs/fuse/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f523f2f..195476a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
flush_dcache_page(page);
+ iov_iter_advance(ii, tmp);
if (!tmp) {
unlock_page(page);
page_cache_release(page);
@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
req->page_descs[req->num_pages].length = tmp;
req->num_pages++;
- iov_iter_advance(ii, tmp);
count += tmp;
pos += tmp;
offset += tmp;
--
2.4.3
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