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@xxxxxxxxxx> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> 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@xxxxxxx> Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
