On Wed, Jun 30, 2021 at 06:54:44PM -0700, Andrew Morton wrote: > From: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > Subject: procfs: allow reading fdinfo with PTRACE_MODE_READ > > 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. > > Since fdinfo doesn't permit reading process memory and manipulating > process state, allow accessing fdinfo under PTRACE_MODE_READ_FSCRED. > > Link: https://lkml.kernel.org/r/20210308170651.919148-1-kaleshsingh@xxxxxxxxxx > Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > Suggested-by: Jann Horn <jannh@xxxxxxxxxx> > Acked-by: Christian König <christian.koenig@xxxxxxx> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> > Cc: Alexey Gladkov <gladkov.alexey@xxxxxxxxx> > Cc: Andrei Vagin <avagin@xxxxxxxxx> > Cc: Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> > Cc: Christian Brauner <christian.brauner@xxxxxxxxxx> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Cc: Helge Deller <deller@xxxxxx> > Cc: Hridya Valsaraju <hridya@xxxxxxxxxx> > Cc: James Morris <jamorris@xxxxxxxxxxxxxxxxxxx> > Cc: Jeff Vander Stoep <jeffv@xxxxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Michel Lespinasse <walken@xxxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Cc: Szabolcs Nagy <szabolcs.nagy@xxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- Rather useful (also for CRIU and others). Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
