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Message-ID: <425ab528-7d9a-975a-7f4c-5f903cedd8bc@huawei.com> Date: Sat, 16 Jul 2022 10:33:30 +0800 From: Baokun Li <libaokun1@...wei.com> To: Greg KH <gregkh@...uxfoundation.org> CC: <stable@...r.kernel.org>, <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>, <ritesh.list@...il.com>, <lczerner@...hat.com>, <enwlinux@...il.com>, <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>, <yebin10@...wei.com>, <yukuai3@...wei.com>, Hulk Robot <hulkci@...wei.com>, Baokun Li <libaokun1@...wei.com> Subject: Re: [PATCH 4.19] ext4: fix race condition between ext4_ioctl_setflags and ext4_fiemap 在 2022/7/15 22:10, Greg KH 写道: > On Fri, Jul 15, 2022 at 10:39:28AM +0800, Baokun Li wrote: >> This patch and problem analysis is based on v4.19 LTS. >> The d3b6f23f7167("ext4: move ext4_fiemap to use iomap framework") patch >> is incorporated in v5.7-rc1. This patch avoids this problem by switching >> to iomap in ext4_fiemap. >> >> Hulk Robot reported a BUG on stable 4.19.252: >> ================================================================== >> kernel BUG at fs/ext4/extents_status.c:762! >> invalid opcode: 0000 [#1] SMP KASAN PTI >> CPU: 7 PID: 2845 Comm: syz-executor Not tainted 4.19.252 #46 >> RIP: 0010:ext4_es_cache_extent+0x30e/0x370 >> [...] >> Call Trace: >> ext4_cache_extents+0x238/0x2f0 >> ext4_find_extent+0x785/0xa40 >> ext4_fiemap+0x36d/0xe90 >> do_vfs_ioctl+0x6af/0x1200 >> [...] >> ================================================================== >> >> Above issue may happen as follows: >> ------------------------------------- >> cpu1 cpu2 >> _____________________|_____________________ >> do_vfs_ioctl >> ext4_ioctl >> ext4_ioctl_setflags >> ext4_ind_migrate >> do_vfs_ioctl >> ioctl_fiemap >> ext4_fiemap >> ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) >> ext4_fill_fiemap_extents >> down_write(&EXT4_I(inode)->i_data_sem); >> ext4_ext_check_inode >> ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS) >> memset(ei->i_data, 0, sizeof(ei->i_data)) >> up_write(&EXT4_I(inode)->i_data_sem); >> down_read(&EXT4_I(inode)->i_data_sem); >> ext4_find_extent >> ext4_cache_extents >> ext4_es_cache_extent >> BUG_ON(end < lblk) >> >> We can easily reproduce this problem with the syzkaller testcase: >> ``` >> 02:37:07 executing program 3: >> r0 = openat(0xffffffffffffff9c, &(0x7f0000000040)='./file0\x00', 0x26e1, 0x0) >> ioctl$FS_IOC_FSSETXATTR(r0, 0x40086602, &(0x7f0000000080)={0x17e}) >> mkdirat(0xffffffffffffff9c, &(0x7f00000000c0)='./file1\x00', 0x1ff) >> r1 = openat(0xffffffffffffff9c, &(0x7f0000000100)='./file1\x00', 0x0, 0x0) >> ioctl$FS_IOC_FIEMAP(r1, 0xc020660b, &(0x7f0000000180)={0x0, 0x1, 0x0, 0xef3, 0x6, []}) (async, rerun: 32) >> ioctl$FS_IOC_FSSETXATTR(r1, 0x40086602, &(0x7f0000000140)={0x17e}) (rerun: 32) >> ``` >> >> To solve this issue, we use __generic_block_fiemap() instead of >> generic_block_fiemap() and add inode_lock_shared to avoid race condition. >> >> Reported-by: Hulk Robot <hulkci@...wei.com> >> Signed-off-by: Baokun Li <libaokun1@...wei.com> >> --- >> fs/ext4/extents.c | 15 +++++++++++---- >> 1 file changed, 11 insertions(+), 4 deletions(-) > What is the git commit id of this change in Linus's tree? > > If it is not in Linus's tree, why not? > > confused, > > greg k-h > . This patch does not exist in the Linus' tree. This problem persists until the patch d3b6f23f7167("ext4: move ext4_fiemap to use iomap framework") is incorporated in v5.7-rc1. However, this problem can be found by asserting after patch 4068664e3cd2 ("ext4: fix extent_status fragmentation for plain files") is incorporated into v5.6-rc1. If someone don't want to convert ext4_fiemap to iomap, this patch may help. I also CC linux-ext4 in hopes of getting some advice. Feel free to improve it if something wrong. Thanks a lot! -- With Best Regards, Baokun Li
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