On 2/5/21 1:33 PM, Kalesh Singh 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 Tangential: Please just use ASCII "'" -- it's good enough. > 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. > > Since fdinfo doesn't permit reading process memory and manipulating > process state, allow accessing fdinfo under PTRACE_MODE_READ_FSCRED. > > Suggested-by: Jann Horn <jannh@xxxxxxxxxx> > Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > --- > Changes in v2: > - Update patch description > > fs/proc/base.c | 4 ++-- > fs/proc/fd.c | 15 ++++++++++++++- > 2 files changed, 16 insertions(+), 3 deletions(-) -- ~Randy
