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Previously, ext4_get_group_info() would treat an invalid group number as BUG(), since in theory it should never happen. However, if a malicious attaker (or fuzzer) modifies the superblock via the block device while it is the file system is mounted, it is possible for s_first_data_block to get set to a very large number. In that case, when calculating the block group of some block number (such as the starting block of a preallocation region), could result in an underflow and very large block group number. Then the BUG_ON check in ext4_get_group_info() would fire, resutling in a denial of service attack that can be triggered by root or someone with write access to the block device. For a quality of implementation perspective, it's best that even if the system administrator does something that they shouldn't, that it will not trigger a BUG. So instead of BUG'ing, ext4_get_group_info() will call ext4_error and return NULL. We also add fallback code in all of the callers of ext4_get_group_info() that it might NULL. Also, since ext4_get_group_info() was already borderline to be an inline function, un-inline it. The results in a next reduction of the compiled text size of ext4 by roughly 2k. Cc: stable@kernel.org Link: https://lore.kernel.org/r/20230430154311.579720-2-tytso@mit.edu Reported-by: syzbot+e2efa3efc15a1c9e95c3@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=69b28112e098b070f639efb356393af3ffec4220 Signed-off-by: Theodore Ts'o <tytso@mit.edu> Reviewed-by: Jan Kara <jack@suse.cz> |
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| .. | ||
| .kunitconfig | ||
| acl.c | ||
| acl.h | ||
| balloc.c | ||
| bitmap.c | ||
| block_validity.c | ||
| crypto.c | ||
| dir.c | ||
| ext4.h | ||
| ext4_extents.h | ||
| ext4_jbd2.c | ||
| ext4_jbd2.h | ||
| extents.c | ||
| extents_status.c | ||
| extents_status.h | ||
| fast_commit.c | ||
| fast_commit.h | ||
| file.c | ||
| fsmap.c | ||
| fsmap.h | ||
| fsync.c | ||
| hash.c | ||
| ialloc.c | ||
| indirect.c | ||
| inline.c | ||
| inode-test.c | ||
| inode.c | ||
| ioctl.c | ||
| Kconfig | ||
| Makefile | ||
| mballoc.c | ||
| mballoc.h | ||
| migrate.c | ||
| mmp.c | ||
| move_extent.c | ||
| namei.c | ||
| orphan.c | ||
| page-io.c | ||
| readpage.c | ||
| resize.c | ||
| super.c | ||
| symlink.c | ||
| sysfs.c | ||
| truncate.h | ||
| verity.c | ||
| xattr.c | ||
| xattr.h | ||
| xattr_hurd.c | ||
| xattr_security.c | ||
| xattr_trusted.c | ||
| xattr_user.c | ||