From: Tao Cui BLKTRACESETUP allocates user-sized relay buffers and sets up a trace that outlives the creating fd. Every command of the interface, BLKTRACESETUP, BLKTRACESETUP2, BLKTRACESTART, BLKTRACESTOP, BLKTRACETEARDOWN and, on x86_64 with CONFIG_COMPAT, the 32-bit variant can be issued by anyone who can open the block device node, and the sysfs trace attribute group reaches the same tracing state without any check. A container that is handed the node can hold trace state and relay memory on a shared queue; the relay files themselves stay root-only (0400). Gate blk_trace_ioctl() and sysfs_blk_trace_attr_store() with CAP_SYS_ADMIN. The ioctls return -EPERM, the sysfs store -EACCES like the md store callbacks it resembles. Unprivileged callers now get one answer that depends only on their credentials, instead of values that revealed whether a trace existed and was running. Traces survive the creating fd by design, so a creator that drops its privileges can no longer tear down its own trace. Such traces wait for a privileged teardown or for the queue to go away; blk_trace_remove() from sg_device_destroy() and blk_trace_shutdown() from blk_unregister_queue() bound that wait for unplugged devices. Document the sysfs attributes in Documentation/ABI, where the group has been missing since it was added. Signed-off-by: Tao Cui --- Documentation/ABI/stable/sysfs-block | 18 ++++++++++++++++++ kernel/trace/blktrace.c | 6 ++++++ 2 files changed, 24 insertions(+) diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block index 900b3fc4c72d..177c4b95a47d 100644 --- a/Documentation/ABI/stable/sysfs-block +++ b/Documentation/ABI/stable/sysfs-block @@ -939,3 +939,21 @@ Description: == ============================================== For more details refer Documentation/admin-guide/iostats.rst + + +What: /sys/block//trace/{enable,act_mask,pid,start_lba,end_lba} + /sys/block///trace/{enable,act_mask,pid,start_lba,end_lba} +Date: January 2009 +Contact: Steven Rostedt , Masami Hiramatsu +Description: + Configure blktrace for this device's request queue. + "enable" creates (1) or removes (0) the per-queue trace + bookkeeping; "act_mask" selects the traced action + categories, either as a number or as a list of category + names; "pid" restricts tracing to one process; + "start_lba" and "end_lba" bound the traced sector range. + Reading an attribute shows the current setting and needs + no privilege; writing any attribute requires + CAP_SYS_ADMIN. Enabling from sysfs does not set up + relay buffers; full tracing is armed through the + BLKTRACESETUP ioctl. diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 8cd2520b4c99..f56d57a924bf 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -927,6 +927,9 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) int ret, start = 0; char b[BDEVNAME_SIZE]; + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + switch (cmd) { case BLKTRACESETUP2: snprintf(b, sizeof(b), "%pg", bdev); @@ -2079,6 +2082,9 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev, u64 value; ssize_t ret = -EINVAL; + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + if (count == 0) goto out; -- 2.53.0