On Mon, Nov 7, 2022 at 10:10 AM syzbot <syzbot+9767be679ef5016b6082@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hello, > > syzbot found the following issue on: > > HEAD commit: 968c2729e576 x86: kmsan: fix comment in kmsan_shadow.c > git tree: https://github.com/google/kmsan.git master > console output: https://syzkaller.appspot.com/x/log.txt?x=11d01ad6880000 > kernel config: https://syzkaller.appspot.com/x/.config?x=131312b26465c190 > dashboard link: https://syzkaller.appspot.com/bug?extid=9767be679ef5016b6082 > compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project.git 610139d2d9ce6746b3c617fb3e2f7886272d26ff), GNU ld (GNU Binutils for Debian) 2.35.2 > userspace arch: i386 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/c78ce21b953f/disk-968c2729.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/22868d826804/vmlinux-968c2729.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+9767be679ef5016b6082@xxxxxxxxxxxxxxxxxxxxxxxxx > > ===================================================== > BUG: KMSAN: uninit-value in pagecache_write+0x655/0x720 fs/ext4/verity.c:91 > pagecache_write+0x655/0x720 fs/ext4/verity.c:91 > ext4_write_merkle_tree_block+0x84/0xa0 fs/ext4/verity.c:389 > build_merkle_tree_level+0x972/0x1250 fs/verity/enable.c:121 > build_merkle_tree fs/verity/enable.c:182 [inline] > enable_verity+0xede/0x1920 fs/verity/enable.c:268 > fsverity_ioctl_enable+0x895/0xab0 fs/verity/enable.c:392 > __ext4_ioctl fs/ext4/ioctl.c:1572 [inline] > ext4_ioctl+0x26dd/0x8c50 fs/ext4/ioctl.c:1606 > ext4_compat_ioctl+0x702/0x800 fs/ext4/ioctl.c:1682 > __do_compat_sys_ioctl fs/ioctl.c:968 [inline] > __se_compat_sys_ioctl+0x781/0xfa0 fs/ioctl.c:910 > __ia32_compat_sys_ioctl+0x8f/0xd0 fs/ioctl.c:910 > do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] > __do_fast_syscall_32+0xa2/0x100 arch/x86/entry/common.c:178 > do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203 > do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:246 > entry_SYSENTER_compat_after_hwframe+0x70/0x82 > > Local variable fsdata created at: > pagecache_write+0x21c/0x720 fs/ext4/verity.c:85 > ext4_write_merkle_tree_block+0x84/0xa0 fs/ext4/verity.c:389 > > CPU: 1 PID: 15121 Comm: syz-executor.3 Not tainted 6.0.0-rc5-syzkaller-48543-g968c2729e576 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022 > ===================================================== This is identical to other reports fixed in https://lore.kernel.org/lkml/20220915150417.722975-43-glider@xxxxxxxxxx/ To fix the error, we need to initialize fsdata explicitly, because aops->write_begin is not guaranteed to do so: ============================================================================= ext4: initialize fsdata in pagecache_write() When aops->write_begin() does not initialize fsdata, KMSAN reports an error passing the latter to aops->write_end(). Fix this by unconditionally initializing fsdata. Fixes: c93d8f885809 ("ext4: add basic fs-verity support") Reported-by: syzbot+9767be679ef5016b6082@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c index 3c640bd7ecaeb..30e3b65798b50 100644 --- a/fs/ext4/verity.c +++ b/fs/ext4/verity.c @@ -79,7 +79,7 @@ static int pagecache_write(struct inode *inode, const void *buf, size_t count, size_t n = min_t(size_t, count, PAGE_SIZE - offset_in_page(pos)); struct page *page; - void *fsdata; + void *fsdata = NULL; int res; res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata); =============================================================================
