On Thu, Jan 28, 2021 at 1:24 PM Kalesh Singh [off-list ref] wrote:

Android captures per-process system memory state when certain low memory
events (e.g a foreground app kill) occur, to identify potential memory
hoggers. In order to measure how much memory a process actually consumes,
it is necessary to include the DMA buffer sizes for that process in the
memory accounting. Since the handle to DMA buffers are raw FDs, it is
important to be able to identify which processes have FD references to
a DMA buffer.

Currently, DMA buffer FDs can be accounted using /proc/<pid>/fd/* and
/proc/<pid>/fdinfo -- both are only readable by the process owner,
as follows:
  1. Do a readlink on each FD.
  2. If the target path begins with "/dmabuf", then the FD is a dmabuf FD.
  3. stat the file to get the dmabuf inode number.
  4. Read/ proc/<pid>/fdinfo/<fd>, to get the DMA buffer size.

Accessing other processes’ fdinfo requires root privileges. This limits
the use of the interface to debugging environments and is not suitable
for production builds.  Granting root privileges even to a system process
increases the attack surface and is highly undesirable.

This series proposes making the requirement to read fdinfo less strict
with PTRACE_MODE_READ.

Hi everyone,

I will send v2 of this patch series. Please let me know if you have
any other comments or feedback, that should be addressed in the new
version.

Thanks,
Kalesh

Kalesh Singh (2):
  procfs: Allow reading fdinfo with PTRACE_MODE_READ
  dmabuf: Add dmabuf inode no to fdinfo

 drivers/dma-buf/dma-buf.c |  1 +
 fs/proc/base.c            |  4 ++--
 fs/proc/fd.c              | 15 ++++++++++++++-
 3 files changed, 17 insertions(+), 3 deletions(-)

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2.30.0.365.g02bc693789-goog