e4571b8c5e
[BUG] It's easy to trigger NULL pointer dereference, just by removing a non-existing device id: # mkfs.btrfs -f -m single -d single /dev/test/scratch1 \ /dev/test/scratch2 # mount /dev/test/scratch1 /mnt/btrfs # btrfs device remove 3 /mnt/btrfs Then we have the following kernel NULL pointer dereference: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 9 PID: 649 Comm: btrfs Not tainted 5.14.0-rc3-custom+ #35 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:btrfs_rm_device+0x4de/0x6b0 [btrfs] btrfs_ioctl+0x18bb/0x3190 [btrfs] ? lock_is_held_type+0xa5/0x120 ? find_held_lock.constprop.0+0x2b/0x80 ? do_user_addr_fault+0x201/0x6a0 ? lock_release+0xd2/0x2d0 ? __x64_sys_ioctl+0x83/0xb0 __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae [CAUSE] Commit a27a94c2b0c7 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly") moves the "missing" device path check into btrfs_rm_device(). But btrfs_rm_device() itself can have case where it only receives @devid, with NULL as @device_path. In that case, calling strcmp() on NULL will trigger the NULL pointer dereference. Before that commit, we handle the "missing" case inside btrfs_find_device_by_devspec(), which will not check @device_path at all if @devid is provided, thus no way to trigger the bug. [FIX] Before calling strcmp(), also make sure @device_path is not NULL. Fixes: a27a94c2b0c7 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly") CC: stable@vger.kernel.org # 5.4+ Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.