4a4ac4eba1
The patch fixes a race between ftruncate(2), mmap-ed write and write(2): 1) An user makes a page dirty via mmap-ed write. 2) The user performs shrinking truncate(2) intended to purge the page. 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to writeback. fuse_writepage_locked fills FUSE_WRITE request and releases the original page by end_page_writeback. 4) fuse_do_setattr() completes and successfully returns. Since now, i_mutex is free. 5) Ordinary write(2) extends i_size back to cover the page. Note that fuse_send_write_pages do wait for fuse writeback, but for another page->index. 6) fuse_writepage_locked proceeds by queueing FUSE_WRITE request. fuse_send_writepage is supposed to crop inarg->size of the request, but it doesn't because i_size has already been extended back. Moving end_page_writeback to the end of fuse_writepage_locked fixes the race because now the fact that truncate_pagecache is successfully returned infers that fuse_writepage_locked has already called end_page_writeback. And this, in turn, infers that fuse_flush_writepages has already called fuse_send_writepage, and the latter used valid (shrunk) i_size. write(2) could not extend it because of i_mutex held by ftruncate(2). Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Cc: stable@vger.kernel.org |
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| .. | ||
| control.c | ||
| cuse.c | ||
| dev.c | ||
| dir.c | ||
| file.c | ||
| fuse_i.h | ||
| inode.c | ||
| Kconfig | ||
| Makefile | ||