diff options
| author | Dominik Maier <dmnk@google.com> | 2026-10-25 21:07:40 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-10-26 20:34:31 -0600 |
| commit | 87409eedc543d288cdd49c2174f7d61eca7b8db5 (patch) | |
| tree | 05f67acff23aa5b84471e2baaef119b3e4f02b23 | |
| parent | 3d97e7c377f1a8fac1c5bf8fd6008c9a67c87847 (diff) | |
loop: check for read-write open mode on LOOP_SET_STATUS in lo_compat_ioctl()
lo_ioctl() checks for (mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN)
before allowing LOOP_SET_STATUS or LOOP_SET_STATUS64, but not
lo_compat_ioctl(), the handler used by 32-bit user space on 64-bit
kernels.
As a result, on 64-bit kernels with CONFIG_COMPAT=y, a 32-bit
unprivileged user-space process holding a read-only (O_RDONLY) file
descriptor to an active /dev/loopN device can issue a compat
LOOP_SET_STATUS ioctl to modify lo_offset, clear lo_sizelimit to 0
(exposing backing-file data past the configured limit), or alter
lo_flags.
Enforce the same (mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN) check
on LOOP_SET_STATUS in lo_compat_ioctl().
Cc: stable@vger.kernel.org
Assisted-by: ARTIST LLM
Signed-off-by: Dominik Maier <dmnk@google.com>
Reviewed-by: Bart Van Assche bvanassche@acm.org
Link: https://patch.msgid.link/20261025200740.2064379-1-dmnk@google.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | drivers/block/loop.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index aabaaacdb4fa..a3325ceab484 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1604,8 +1604,10 @@ static int lo_compat_ioctl(struct block_device *bdev, blk_mode_t mode, switch(cmd) { case LOOP_SET_STATUS: - err = loop_set_status_compat(lo, - (const struct compat_loop_info __user *)arg); + err = -EPERM; + if ((mode & BLK_OPEN_WRITE) || capable(CAP_SYS_ADMIN)) + err = loop_set_status_compat(lo, + (const struct compat_loop_info __user *)arg); break; case LOOP_GET_STATUS: err = loop_get_status_compat(lo, |