Re: [PATCH] ext3: fix a bug when we try to open a file with O_TMPFILE flag

[Jan Kara <jack@suse.cz>]

On Sun 21-07-13 00:53:47, Zheng Liu wrote:
> From: Zheng Liu <wenqing.lz@taobao.com>
> 
> When we try to open a file with O_TMPFILE flag, we will trigger a bug.
> The root cause is that in ext4_orphan_add() we check ->i_nlink == 0 and
> this check always fails because we set ->i_nlink = 1 in
> inode_init_always().  We can use the following program to trigger it:
> 
> int main(int argc, char *argv[])
> {
> 	int fd;
> 
> 	fd = open(argv[1], O_TMPFILE, 0666);
> 	if (fd < 0) {
> 		perror("open ");
> 		return -1;
> 	}
> 	close(fd);
> 	return 0;
> }
> 
> The oops message looks like this:
> 
> kernel: kernel BUG at fs/ext3/namei.c:1992!
> kernel: invalid opcode: 0000 [#1] SMP
> kernel: Modules linked in: ext4 jbd2 crc16 cpufreq_ondemand ipv6 dm_mirror dm_region_hash dm_log dm_mod parport_pc parport serio_raw sg dcdbas pcspkr i2c_i801 ehci_pci ehci_hcd button acpi_cpufreq mperf e1000e ptp pps_core ttm drm_kms_helper drm hwmon i2c_algo_bit i2c_core ext3 jbd sd_mod ahci libahci libata scsi_mod uhci_hcd
> kernel: CPU: 0 PID: 2882 Comm: tst_tmpfile Not tainted 3.11.0-rc1+ #4
> kernel: Hardware name: Dell Inc. OptiPlex 780 /0V4W66, BIOS A05 08/11/2010
> kernel: task: ffff880112d30050 ti: ffff8801124d4000 task.ti: ffff8801124d4000
> kernel: RIP: 0010:[<ffffffffa00db5ae>] [<ffffffffa00db5ae>] ext3_orphan_add+0x6a/0x1eb [ext3]
> kernel: RSP: 0018:ffff8801124d5cc8  EFLAGS: 00010202
> kernel: RAX: 0000000000000000 RBX: ffff880111510128 RCX: ffff8801114683a0
> kernel: RDX: 0000000000000000 RSI: ffff880111510128 RDI: ffff88010fcf65a8
> kernel: RBP: ffff8801124d5d18 R08: 0080000000000000 R09: ffffffffa00d3b7f
> kernel: R10: ffff8801114683a0 R11: ffff8801032a2558 R12: 0000000000000000
> kernel: R13: ffff88010fcf6800 R14: ffff8801032a2558 R15: ffff8801115100d8
> kernel: FS:  00007f5d172b5700(0000) GS:ffff880117c00000(0000) knlGS:0000000000000000
> kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> kernel: CR2: 00007f5d16df15d0 CR3: 0000000110b1d000 CR4: 00000000000407f0
> kernel: Stack:
> kernel: 000000000000000c ffff8801048a7dc8 ffff8801114685a8 ffffffffa00b80d7
> kernel: ffff8801124d5e38 ffff8801032a2558 ffff88010ce24d68 0000000000000000
> kernel: ffff88011146b300 ffff8801124d5d44 ffff8801124d5d78 ffffffffa00db7e1
> kernel: Call Trace:
> kernel: [<ffffffffa00b80d7>] ? journal_start+0x8c/0xbd [jbd]
> kernel: [<ffffffffa00db7e1>] ext3_tmpfile+0xb2/0x13b [ext3]
> kernel: [<ffffffff821076f8>] path_openat+0x11f/0x5e7
> kernel: [<ffffffff821c86b4>] ? list_del+0x11/0x30
> kernel: [<ffffffff82065fa2>] ?  __dequeue_entity+0x33/0x38
> kernel: [<ffffffff82107cd5>] do_filp_open+0x3f/0x8d
> kernel: [<ffffffff82112532>] ? __alloc_fd+0x50/0x102
> kernel: [<ffffffff820f9296>] do_sys_open+0x13b/0x1cd
> kernel: [<ffffffff820f935c>] SyS_open+0x1e/0x20
> kernel: [<ffffffff82398c02>] system_call_fastpath+0x16/0x1b
> kernel: Code: 39 c7 0f 85 67 01 00 00 0f b7 03 25 00 f0 00 00 3d 00 40 00 00 74 18 3d 00 80 00 00 74 11 3d 00 a0 00 00 74 0a 83 7b 48 00 74 04 <0f> 0b eb fe 49 8b 85 50 03 00 00 4c 89 f6 48 c7 c7 c0 99 0e a0
> kernel: RIP  [<ffffffffa00db5ae>] ext3_orphan_add+0x6a/0x1eb [ext3]
> kernel: RSP <ffff8801124d5cc8>
> 
> Here we couldn't call clear_nlink() directly because in d_tmpfile() we
> will call inode_dec_link_count() to decrease ->i_nlink.  So this commit
> tries to call d_tmpfile() before ext4_orphan_add() to fix this problem.
  Thanks the patch looks good. I've added the patch to my tree and will
push it to Linus soon.

								Honza
> 
> Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> ---
>  fs/ext3/namei.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
> index 998ea11..1194b1f 100644
> --- a/fs/ext3/namei.c
> +++ b/fs/ext3/namei.c
> @@ -1780,11 +1780,11 @@ retry:
>  		inode->i_op = &ext3_file_inode_operations;
>  		inode->i_fop = &ext3_file_operations;
>  		ext3_set_aops(inode);
> +		d_tmpfile(dentry, inode);
>  		err = ext3_orphan_add(handle, inode);
>  		if (err)
>  			goto err_drop_inode;
>  		mark_inode_dirty(inode);
> -		d_tmpfile(dentry, inode);
>  		unlock_new_inode(inode);
>  	}
>  	ext3_journal_stop(handle);
> -- 
> 1.7.9.7
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR