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Date: Tue, 14 Jun 2022 18:01:46 +0800 From: Baokun Li <libaokun1@...wei.com> To: Jan Kara <jack@...e.cz> CC: <linux-ext4@...r.kernel.org>, <tytso@....edu>, <adilger.kernel@...ger.ca>, <ritesh.list@...il.com>, <lczerner@...hat.com>, <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>, <yebin10@...wei.com>, <yukuai3@...wei.com>, Hulk Robot <hulkci@...wei.com> Subject: Re: [PATCH] ext4: fix use-after-free in ext4_xattr_set_entry 在 2022/6/14 17:54, Jan Kara 写道: > On Thu 02-06-22 19:46:51, Baokun Li wrote: >> Hulk Robot reported a issue: >> ================================================================== >> BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x18ab/0x3500 >> Write of size 4105 at addr ffff8881675ef5f4 by task syz-executor.0/7092 >> >> CPU: 1 PID: 7092 Comm: syz-executor.0 Not tainted 4.19.90-dirty #17 >> Call Trace: >> [...] >> memcpy+0x34/0x50 mm/kasan/kasan.c:303 >> ext4_xattr_set_entry+0x18ab/0x3500 fs/ext4/xattr.c:1747 >> ext4_xattr_ibody_inline_set+0x86/0x2a0 fs/ext4/xattr.c:2205 >> ext4_xattr_set_handle+0x940/0x1300 fs/ext4/xattr.c:2386 >> ext4_xattr_set+0x1da/0x300 fs/ext4/xattr.c:2498 >> __vfs_setxattr+0x112/0x170 fs/xattr.c:149 >> __vfs_setxattr_noperm+0x11b/0x2a0 fs/xattr.c:180 >> __vfs_setxattr_locked+0x17b/0x250 fs/xattr.c:238 >> vfs_setxattr+0xed/0x270 fs/xattr.c:255 >> setxattr+0x235/0x330 fs/xattr.c:520 >> path_setxattr+0x176/0x190 fs/xattr.c:539 >> __do_sys_lsetxattr fs/xattr.c:561 [inline] >> __se_sys_lsetxattr fs/xattr.c:557 [inline] >> __x64_sys_lsetxattr+0xc2/0x160 fs/xattr.c:557 >> do_syscall_64+0xdf/0x530 arch/x86/entry/common.c:298 >> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >> RIP: 0033:0x459fe9 >> RSP: 002b:00007fa5e54b4c08 EFLAGS: 00000246 ORIG_RAX: 00000000000000bd >> RAX: ffffffffffffffda RBX: 000000000051bf60 RCX: 0000000000459fe9 >> RDX: 00000000200003c0 RSI: 0000000020000180 RDI: 0000000020000140 >> RBP: 000000000051bf60 R08: 0000000000000001 R09: 0000000000000000 >> R10: 0000000000001009 R11: 0000000000000246 R12: 0000000000000000 >> R13: 00007ffc73c93fc0 R14: 000000000051bf60 R15: 00007fa5e54b4d80 >> [...] >> ================================================================== >> >> Above issue may happen as follows: >> ------------------------------------- >> ext4_xattr_set >> ext4_xattr_set_handle >> ext4_xattr_ibody_find >> >> s->end < s->base >> >> no EXT4_STATE_XATTR >> >> xattr_check_inode is not executed >> ext4_xattr_ibody_set >> ext4_xattr_set_entry >> >> size_t min_offs = s->end - s->base >> >> UAF in memcpy >> >> we can easily reproduce this problem with the following commands: >> mkfs.ext4 -F /dev/sda >> mount -o debug_want_extra_isize=128 /dev/sda /mnt >> touch /mnt/file >> setfattr -n user.cat -v `seq -s z 4096|tr -d '[:digit:]'` /mnt/file >> >> In ext4_xattr_ibody_find, we have the following assignment logic: >> header = IHDR(inode, raw_inode) >> = raw_inode + EXT4_GOOD_OLD_INODE_SIZE + i_extra_isize >> is->s.base = IFIRST(header) >> = header + sizeof(struct ext4_xattr_ibody_header) >> is->s.end = raw_inode + s_inode_size >> >> Obviously, when the inode does not have EXT4_status_XATTR and its >> i_extra_isize is large, is->s.end may be larger than is->s.base. >> In this case, the above issue may be triggered. >> >> EXT4_GOOD_OLD_INODE_SIZE extra_isize header entry pad data >> |---------------------------|------------|------|---------|---|--------| >> >> As shown above, when adding an xattr to an inode, we must ensure that the >> inode_size is not less than EXT4_GOOD_OLD_INODE_SIZE + extra_isize + pad. >> >> Reported-by: Hulk Robot <hulkci@...wei.com> >> Signed-off-by: Baokun Li <libaokun1@...wei.com> > Thanks for the fix! It looks good to me. Just one small nit: > >> +#define INODE_HAVE_XATTR_SPACE(inode) \ >> + ((EXT4_I(inode)->i_extra_isize != 0) && \ >> + (EXT4_GOOD_OLD_INODE_SIZE + EXT4_I(inode)->i_extra_isize + \ >> + sizeof(struct ext4_xattr_ibody_header) + EXT4_XATTR_PAD <= \ >> + EXT4_INODE_SIZE((inode)->i_sb))) >> + > We should have ext4 in the name of the above macro so something like: > > EXT4_INODE_HAS_XATTR_SPACE() > > With that fixed feel free to add: > > Reviewed-by: Jan Kara <jack@...e.cz> > > Honza Thank you for your review! I will send a patch V2 with the changes suggested by you. Thanks again! -- With Best Regards, Baokun Li .
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