On Wed, Jul 15, 2020 at 08:16AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: e9919e11 Merge branch 'for-linus' of git://git.kernel.org/.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1217a83b100000 > kernel config: https://syzkaller.appspot.com/x/.config?x=570eb530a65cd98e > dashboard link: https://syzkaller.appspot.com/bug?extid=0f1e470df6a4316e0a11 > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b) > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+0f1e470df6a4316e0a11@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KCSAN: data-race in generic_file_buffered_read / generic_file_buffered_read Our guess is that this is either misuse of an API from userspace, or a bug. Can someone clarify? Below are the snippets of code around these accesses. > write to 0xffff8880968747b0 of 8 bytes by task 6336 on cpu 0: > generic_file_buffered_read+0x18be/0x19e0 mm/filemap.c:2246 ... would_block: error = -EAGAIN; out: ra->prev_pos = prev_index; ra->prev_pos <<= PAGE_SHIFT; 2246) ra->prev_pos |= prev_offset; *ppos = ((loff_t)index << PAGE_SHIFT) + offset; file_accessed(filp); return written ? written : error; } EXPORT_SYMBOL_GPL(generic_file_buffered_read); ... > generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326 > ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74 > call_read_iter include/linux/fs.h:1902 [inline] > generic_file_splice_read+0x22a/0x310 fs/splice.c:312 > do_splice_to fs/splice.c:870 [inline] > splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950 > do_splice_direct+0xf2/0x170 fs/splice.c:1059 > do_sendfile+0x562/0xb10 fs/read_write.c:1540 > __do_sys_sendfile64 fs/read_write.c:1601 [inline] > __se_sys_sendfile64 fs/read_write.c:1587 [inline] > __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587 > do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > read to 0xffff8880968747b0 of 8 bytes by task 6334 on cpu 1: > generic_file_buffered_read+0x11e/0x19e0 mm/filemap.c:2011 ... index = *ppos >> PAGE_SHIFT; prev_index = ra->prev_pos >> PAGE_SHIFT; 2011) prev_offset = ra->prev_pos & (PAGE_SIZE-1); last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; offset = *ppos & ~PAGE_MASK; ... > generic_file_read_iter+0x7d/0x3e0 mm/filemap.c:2326 > ext4_file_read_iter+0x2d6/0x420 fs/ext4/file.c:74 > call_read_iter include/linux/fs.h:1902 [inline] > generic_file_splice_read+0x22a/0x310 fs/splice.c:312 > do_splice_to fs/splice.c:870 [inline] > splice_direct_to_actor+0x2a8/0x660 fs/splice.c:950 > do_splice_direct+0xf2/0x170 fs/splice.c:1059 > do_sendfile+0x562/0xb10 fs/read_write.c:1540 > __do_sys_sendfile64 fs/read_write.c:1601 [inline] > __se_sys_sendfile64 fs/read_write.c:1587 [inline] > __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1587 > do_syscall_64+0x51/0xb0 arch/x86/entry/common.c:384 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 1 PID: 6334 Comm: syz-executor.0 Not tainted 5.8.0-rc5-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > ================================================================== Thanks, -- Marco
