On Monday, September 21, 2020 at 5:32:22 PM UTC+8 syzbot wrote: > > Hello, > > syzbot found the following issue on: > > HEAD commit: 325d0eab Merge branch 'akpm' (patches from Andrew) > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1671c0e3900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=b12e84189082991c > dashboard link: https://syzkaller.appspot.com/bug?extid=690cb1e51970435f9775 > compiler: gcc (GCC) 10.1.0-syz 20200507 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15705a3d900000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=117b3281900000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+690cb1...@xxxxxxxxxxxxxxxxxxxxxxxxx > > REISERFS (device loop0): journal params: device loop0, size 15748, journal first block 18, max trans len 256, max batch 225, max commit age 30, max trans age 30 > REISERFS (device loop0): checking transaction log (loop0) > REISERFS (device loop0): Using tea hash to sort names > REISERFS (device loop0): using 3.5.x disk format > general protection fault, probably for non-canonical address 0xdffffc000000000d: 0000 [#1] PREEMPT SMP KASAN > KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f] > CPU: 0 PID: 6874 Comm: syz-executor834 Not tainted 5.9.0-rc5-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:d_really_is_negative include/linux/dcache.h:472 [inline] > RIP: 0010:reiserfs_xattr_jcreate_nblocks fs/reiserfs/xattr.h:78 [inline] > RIP: 0010:reiserfs_security_init+0x285/0x4d0 fs/reiserfs/xattr_security.c:70 > Code: 48 c1 ea 03 80 3c 02 00 0f 85 2b 02 00 00 4d 8b ad a0 05 00 00 48 b8 00 00 00 00 00 fc ff df 49 8d 7d 68 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 23 02 00 00 49 83 7d 68 00 0f 84 62 01 00 00 48 > RSP: 0018:ffffc90005827980 EFLAGS: 00010202 > RAX: dffffc0000000000 RBX: 0000000000000036 RCX: 000000000000006c > RDX: 000000000000000d RSI: ffffffff82009dd3 RDI: 0000000000000068 > RBP: ffff88807d8441d0 R08: ffffc90005827a10 R09: ffffc90005827a18 > R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000005fa > R13: 0000000000000000 R14: ffff888094e60000 R15: 0000000000000000 > FS: 0000000001036880(0000) GS:ffff8880ae400000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f5a6fb90ab4 CR3: 000000009a1ab000 CR4: 00000000001506f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > reiserfs_mkdir+0x2c9/0x980 fs/reiserfs/namei.c:821 > create_privroot fs/reiserfs/xattr.c:882 [inline] > reiserfs_xattr_init+0x4de/0xb52 fs/reiserfs/xattr.c:1004 int reiserfs_xattr_init(struct super_block *s, int mount_flags) { int err = 0; struct dentry *privroot = REISERFS_SB(s)->priv_root; err = xattr_mount_check(s); if (err) goto error; if (d_really_is_negative(privroot) && !(mount_flags & SB_RDONLY)) { inode_lock(d_inode(s->s_root)); err = create_privroot(REISERFS_SB(s)->priv_root); inode_unlock(d_inode(s->s_root)); } if (d_really_is_positive(privroot)) { inode_lock(d_inode(privroot)); if (!REISERFS_SB(s)->xattr_root) { struct dentry *dentry; dentry = lookup_one_len(XAROOT_NAME, privroot, strlen(XAROOT_NAME)); if (!IS_ERR(dentry)) { pr_alert("assign xattr_root with dentry = 0x%lx", dentry); REISERFS_SB(s)->xattr_root = dentry; }else err = PTR_ERR(dentry); } inode_unlock(d_inode(privroot)); } ...... } >From the implementation of reiserfs_xattr_init, only when d_really_is_positive(privroot) is true, xattr_root could be assigned with a dentry obtained from lookup_one_len. In other words, create_privroot is executed with REISERFS_SB(s)->xattr_root as NULL pointer. With improper implementation of mkdir operation in reiserfs filesystem or accessing the xattr_root in reiserfs_mkdir , it can lead to NULL pointer dereference. If you remove the red code in reiserfs_xattr_jcreate_nblocks, the crash never occurs, but it may affect nblocks calculation in the reiserfs filesystem. static inline size_t reiserfs_xattr_jcreate_nblocks(struct inode *inode) { size_t nblocks = JOURNAL_BLOCKS_PER_OBJECT(inode->i_sb); pr_alert("5: inode = 0x%lx", inode); if ((REISERFS_I(inode)->i_flags & i_has_xattr_dir) == 0) { nblocks += JOURNAL_BLOCKS_PER_OBJECT(inode->i_sb); if (d_really_is_negative(REISERFS_SB(inode->i_sb)->xattr_root)) nblocks += JOURNAL_BLOCKS_PER_OBJECT(inode->i_sb); } return nblocks; } -- My best regards to you. No System Is Safe! Dongliang Mu
