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.
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(-)