Hello, syzbot has tested the proposed patch but the reproducer still triggered crash: BUG: unable to handle kernel NULL pointer dereference in generic_perform_write BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0010) - not-present page PGD a3819067 P4D a3819067 PUD a2ea0067 PMD 0 Oops: 0010 [#1] PREEMPT SMP KASAN CPU: 1 PID: 9214 Comm: syz-executor.1 Not tainted 5.6.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:0x0 Code: Bad RIP value. RSP: 0018:ffffc90006d1fa38 EFLAGS: 00010246 RAX: ffffffff883cb0a0 RBX: 0000000000000000 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffff888082b89a60 RDI: ffff88808a414a80 RBP: ffff888082b89a60 R08: 0000000000000000 R09: ffffc90006d1fac0 R10: ffff888072cd6607 R11: ffffed100e59acc0 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000000 R15: ffffc90006d1fd18 FS: 00007f310f3f3700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 00000000904f1000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: generic_perform_write+0x20a/0x4e0 mm/filemap.c:3302 ext4_buffered_write_iter+0x1f7/0x450 fs/ext4/file.c:270 ext4_file_write_iter+0x1ec/0x13f0 fs/ext4/file.c:642 call_write_iter include/linux/fs.h:1907 [inline] new_sync_write+0x4a2/0x700 fs/read_write.c:484 __vfs_write+0xc9/0x100 fs/read_write.c:497 vfs_write+0x268/0x5d0 fs/read_write.c:559 ksys_write+0x12d/0x250 fs/read_write.c:612 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 entry_SYSCALL_64_after_hwframe+0x49/0xb3 RIP: 0033:0x45c889 Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f310f3f2c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f310f3f36d4 RCX: 000000000045c889 RDX: 0000000000000001 RSI: 0000000020000080 RDI: 0000000000000003 RBP: 000000000076bfa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 0000000000000cdc R14: 00000000004cf042 R15: 000000000076bfac Modules linked in: CR2: 0000000000000000 ---[ end trace ff42a65b331528ba ]--- RIP: 0010:0x0 Code: Bad RIP value. RSP: 0018:ffffc90006d1fa38 EFLAGS: 00010246 RAX: ffffffff883cb0a0 RBX: 0000000000000000 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffff888082b89a60 RDI: ffff88808a414a80 RBP: ffff888082b89a60 R08: 0000000000000000 R09: ffffc90006d1fac0 R10: ffff888072cd6607 R11: ffffed100e59acc0 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000000 R15: ffffc90006d1fd18 FS: 00007f310f3f3700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000076c061 CR3: 00000000904f1000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Tested on: commit: 5b8b9d0c Merge branch 'akpm' (patches from Andrew) git tree: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git console output: https://syzkaller.appspot.com/x/log.txt?x=158b23ca100000 kernel config: https://syzkaller.appspot.com/x/.config?x=23c5a352e32a1944 dashboard link: https://syzkaller.appspot.com/bug?extid=bca9799bf129256190da compiler: gcc (GCC) 9.0.0 20181231 (experimental)
