procfs: add 'size' to /proc/<pid>/fdinfo/

Patch series "procfs: Add file path and size to /proc/<pid>/fdinfo", v2.

Processes can pin shared memory by keeping a handle to it through a
file descriptor; for instance dmabufs, memfd, and ashmem (in Android).

In the case of a memory leak, to identify the process pinning the
memory, userspace needs to:
  - Iterate the /proc/<pid>/fd/* for each process
  - Do a readlink on each entry to identify the type of memory from
    the file path.
  - stat() each entry to get the size of the memory.

The file permissions on /proc/<pid>/fd/* only allows for the owner
or root to perform the operations above; and so is not suitable for
capturing the system-wide state in a production environment.

This issue was addressed for dmabufs by making /proc/*/fdinfo/*
accessible to a process with PTRACE_MODE_READ_FSCREDS credentials[1]
To allow the same kind of tracking for other types of shared memory,
add the following fields to /proc/<pid>/fdinfo/<fd>:

path - This allows identifying the type of memory based on common
       prefixes: e.g. "/memfd...", "/dmabuf...", "/dev/ashmem..."

       This was not an issued when dmabuf tracking was introduced
       because the exp_name field of dmabuf fdinfo could be used
       to distinguish dmabuf fds from other types.

size - To track the amount of memory that is being pinned.

       dmabufs expose size as an additional field in fdinfo. Remove
       this and make it a common field for all fds.

Access to /proc/<pid>/fdinfo is governed by PTRACE_MODE_READ_FSCREDS
-- the same as for /proc/<pid>/maps which also exposes the path and
size for mapped memory regions.

This allows for a system process with PTRACE_MODE_READ_FSCREDS to
account the pinned per-process memory via fdinfo.

This patch (of 2):

To be able to account the amount of memory a process is keeping pinned by
open file descriptors add a 'size' field to fdinfo output.

dmabufs fds already expose a 'size' field for this reason, remove this and
make it a common field for all fds.  This allows tracking of other types
of memory (e.g.  memfd and ashmem in Android).

Link: https://lkml.kernel.org/r/20220623220613.3014268-1-kaleshsingh@google.com
Link: https://lkml.kernel.org/r/20220623220613.3014268-2-kaleshsingh@google.com
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Ioannis Ilkos <ilkos@google.com>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Cc: Colin Cross <ccross@google.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 979b699e7d14f638cac55c39e640df491e718d81..22d65d755ad20b45eaaa8f9948168b10361cfafb 100644 (file)
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1891,13 +1891,14 @@ if precise results are needed.
 3.8    /proc/<pid>/fdinfo/<fd> - Information about opened file
 ---------------------------------------------------------------
 This file provides information associated with an opened file. The regular
-files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
+files have at least five fields -- 'pos', 'flags', 'mnt_id', 'ino', and 'size'.
+
 The 'pos' represents the current offset of the opened file in decimal
 form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
 file has been created with [see open(2) for details] and 'mnt_id' represents
 mount ID of the file system containing the opened file [see 3.5
 /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
-the file.
+the file, and 'size' represents the size of the file in bytes.
 
 A typical output is::
 
@@ -1905,6 +1906,7 @@ A typical output is::
        flags:  0100002
        mnt_id: 19
        ino:    63107
+       size:   0
 
 All locks associated with a file descriptor are shown in its fdinfo too::
 
@@ -1922,6 +1924,7 @@ Eventfd files
        flags:  04002
        mnt_id: 9
        ino:    63107
+       size:   0
        eventfd-count:  5a
 
 where 'eventfd-count' is hex value of a counter.
@@ -1935,6 +1938,7 @@ Signalfd files
        flags:  04002
        mnt_id: 9
        ino:    63107
+       size:   0
        sigmask:        0000000000000200
 
 where 'sigmask' is hex value of the signal mask associated
@@ -1949,6 +1953,7 @@ Epoll files
        flags:  02
        mnt_id: 9
        ino:    63107
+       size:   0
        tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
 
 where 'tfd' is a target file descriptor number in decimal form,
@@ -1967,6 +1972,7 @@ For inotify files the format is the following::
        flags:  02000000
        mnt_id: 9
        ino:    63107
+       size:   0
        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
 
 where 'wd' is a watch descriptor in decimal form, i.e. a target file
@@ -1990,6 +1996,7 @@ For fanotify files the format is::
        flags:  02
        mnt_id: 9
        ino:    63107
+       size:   0
        fanotify flags:10 event-flags:0
        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
@@ -2015,6 +2022,7 @@ Timerfd files
        flags:  02
        mnt_id: 9
        ino:    63107
+       size:   0
        clockid: 0
        ticks: 0
        settime flags: 01

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 32f55640890ce5cfda4f8bfbd7c88a230054c5ea..5f2ae38c960fd5905babef71b260835334e6f698 100644 (file)
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -378,7 +378,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
 {
        struct dma_buf *dmabuf = file->private_data;
 
-       seq_printf(m, "size:\t%zu\n", dmabuf->size);
        /* Don't count the temporary reference taken inside procfs seq_show */
        seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
        seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name);

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 913bef0d2a36c4ed0d49dfba1b18cac612cdbe5f..464bc3f557596b7fd73e8410214cc2bcd0e613dc 100644 (file)
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -54,10 +54,11 @@ static int seq_show(struct seq_file *m, void *v)
        if (ret)
                return ret;
 
-       seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\n",
-                  (long long)file->f_pos, f_flags,
-                  real_mount(file->f_path.mnt)->mnt_id,
-                  file_inode(file)->i_ino);
+       seq_printf(m, "pos:\t%lli\n", (long long)file->f_pos);
+       seq_printf(m, "flags:\t0%o\n", f_flags);
+       seq_printf(m, "mnt_id:\t%i\n", real_mount(file->f_path.mnt)->mnt_id);
+       seq_printf(m, "ino:\t%lu\n", file_inode(file)->i_ino);
+       seq_printf(m, "size:\t%lli\n", (long long)file_inode(file)->i_size);
 
        /* show_fd_locks() never deferences files so a stale value is safe */
        show_fd_locks(m, file, files);