linux-kernel - Re: null-ptr-deref due to "ext4: fix potential race between online resizing and write operations"

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Date:   Fri, 21 Feb 2020 19:58:01 +0000
From:   "Jitindar SIngh, Suraj" <surajjs@...zon.com>
To:     "cai@....pw" <cai@....pw>
CC:     "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "paulmck@...nel.org" <paulmck@...nel.org>,
        "tytso@....edu" <tytso@....edu>
Subject: Re: null-ptr-deref due to "ext4: fix potential race between online
 resizing and write operations"

On Fri, 2020-02-21 at 09:02 -0500, Qian Cai wrote:
> Reverted the linux-next commit c20bac9bf82c ("ext4: fix potential
> race between
> s_flex_groups online resizing and access") fixed the crash below
> (with line
> numbers),

Good catch, this is a bug where the dereference of the array
s_flex_groups needs to happen after the "if (flex_size > 1)" if
statement in fs/ext4/ialloc.c:373

> 
> struct flex_groups *flex_group = sbi_array_rcu_deref(EXT4_SB(sb),
>                                                      s_flex_groups,
> g);
> 
> [  575.924527][T13183] LTP: starting fanotify13
> [  576.010554][T31835] /dev/zero: Can't open blockdev
> [  576.867392][T31835] EXT4-fs (loop0): mounting ext3 file system
> using the ext4
> subsystem
> [  576.919604][T31835] EXT4-fs (loop0): mounted filesystem with
> ordered data
> mode. Opts: (null)
> [  576.920112][T31835] ext3 filesystem being mounted at /tmp/ltp-
> ZMONVGlgwi/o0A0RE/mntpoint supports timestamps until 2038
> (0x7fffffff)
> [  576.948501][T31854] BUG: Kernel NULL pointer dereference on read
> at
> 0x00000070
> [  576.948550][T31854] Faulting instruction address:
> 0xc008000010501bfc
> [  576.948573][T31854] Oops: Kernel access of bad area, sig: 11 [#1]
> [  576.948575][    C2] irq event stamp: 107073312
> [  576.948583][    C2] hardirqs last  enabled at (107073312):
> [<c00000000099a174>] _raw_spin_unlock_irqrestore+0x94/0xd0
> [  576.948595][T31854] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=256
> DEBUG_PAGEALLOC NUMA PowerNV
> [  576.948598][T31854] Modules linked in: brd ext4 crc16 mbcache jbd2
> loop
> ip_tables x_tables xfs sd_mod bnx2x ahci libahci mdio libata tg3
> libphy
> firmware_class dm_mirror dm_region_hash dm_log dm_mod
> [  576.948614][    C2] hardirqs last disabled at (107073311):
> [<c000000000999e0c>] _raw_spin_lock_irqsave+0x3c/0xa0
> [  576.948646][T31854] CPU: 52 PID: 31854 Comm: fanotify13 Not
> tainted 5.6.0-
> rc2-next-20200221 #7
> [  576.948689][    C2] softirqs last  enabled at (107073296):
> [<c000000000113b3c>] irq_enter+0x8c/0xc0
> [  576.948693][    C2] softirqs last disabled at (107073297):
> [<c000000000113cdc>] irq_exit+0x16c/0x1d0
> [  576.948754][T31854] NIP:  c008000010501bfc LR: c008000010501d94
> CTR:
> c0000000001f1e30
> [  576.948758][T31854] REGS: c00000129f56f700 TRAP: 0300   Not
> tainted  (5.6.0-
> rc2-next-20200221)
> [  576.948945][T31854] MSR:  9000000000009033
> <SF,HV,EE,ME,IR,DR,RI,LE>  CR:
> 24004224  XER: 20040000
> [  576.948982][T31854] CFAR: c008000010501d9c DAR: 0000000000000070
> DSISR:
> 40000000 IRQMASK: 0 
> [  576.948982][T31854] GPR00: c008000010501d94 c00000129f56f990
> c0080000105c1600
> 0000000000000001 
> [  576.948982][T31854] GPR04: c000000001510808 0000000000000008
> 0000000005cf0ca2
> fffffffe5ca98558 
> [  576.948982][T31854] GPR08: 0000000000000001 0000000000000070
> 0000000000000000
> c00800001057b690 
> [  576.948982][T31854] GPR12: c0000000001f1e30 c000001ffffd5600
> 000000000000000e
> 00000000000007ff 
> [  576.948982][T31854] GPR16: c00000129f56fa20 000000000000fff5
> 0000000000000001
> 0000000000001dbc 
> [  576.948982][T31854] GPR20: 0000000000000000 000000000000002e
> 0000000000000800
> 0000000000000020 
> [  576.948982][T31854] GPR24: 000000000000000e 0000000000000000
> 0000000000000000
> c000000001510808 
> [  576.948982][T31854] GPR28: c000001206b8d000 c0080000105d8227
> c00000129f56fa20
> 0000000000000001 
> [  576.949200][T31854] NIP [c008000010501bfc]
> get_orlov_stats+0x114/0x390 [ext4]
> get_orlov_stats at fs/ext4/ialloc.c:373 (discriminator 11)
> [  576.949232][T31854] LR [c008000010501d94]
> get_orlov_stats+0x2ac/0x390 [ext4]
> [  576.949243][T31854] Call Trace:
> [  576.949260][T31854] [c00000129f56f990] [c008000010501d94]
> get_orlov_stats+0x2ac/0x390 [ext4] (unreliable)
> get_orlov_stats at fs/ext4/ialloc.c:373 (discriminator 11)
> [  576.949301][T31854] [c00000129f56f9f0] [c00800001050231c]
> find_group_orlov+0x4a4/0x6b0 [ext4]
> find_group_orlov at fs/ext4/ialloc.c:467
> [  576.949334][T31854] [c00000129f56fae0] [c0080000105055c8]
> __ext4_new_inode+0x1450/0x23c0 [ext4]
> [  576.949367][T31854] [c00000129f56fc50] [c008000010547f2c]
> ext4_mkdir+0x104/0x590 [ext4]
> [  576.949399][T31854] [c00000129f56fd60] [c0000000004cbc64]
> vfs_mkdir+0x114/0x210
> [  576.949432][T31854] [c00000129f56fda0] [c0000000004d1a70]
> do_mkdirat+0xb0/0x1a0
> [  576.949454][T31854] [c00000129f56fe20] [c00000000000b378]
> system_call+0x5c/0x68
> [  576.949465][T31854] Instruction dump:
> [  576.949473][T31854] 3c620000 e8638730 7f44d378 38630068 48078ccd
> e8410018
> 60000000 60000000 
> [  576.949497][T31854] 60000000 73490001 4182019c 7b091f24 <7f59482a>
> 4807a0d1
> e8410018 2fa30000 
> [  576.949522][T31854] ---[ end trace de4acb29e0d7791c ]---
> [  577.200573][T31854] 
> [  578.200652][T31854] Kernel panic - not syncing: Fatal exception
> [  579