[Linaro-mm-sig] Re: [RFC PATCH] procfs: Add file path and size to /proc/<pid>/fdinfo

Am 19.05.22 um 23:40 schrieb Kalesh Singh:

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

I think this should be split into two patches, one adding the size and one adding the path.

Adding the size is completely unproblematic, but the path might raise some eyebrows.

[1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kerne...

Signed-off-by: Kalesh Singh kaleshsingh@google.com

Documentation/filesystems/proc.rst | 22 ++++++++++++++++++++-- drivers/dma-buf/dma-buf.c | 1 - fs/proc/fd.c | 9 +++++++-- 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 061744c436d9..ad66d78aca51 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -1922,13 +1922,16 @@ 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 six fields -- 'pos', 'flags', 'mnt_id', 'ino', 'size', +and 'path'.

• 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, 'size' represents the size of the file in bytes, and 'path' +represents the file path. A typical output is:: @@ -1936,6 +1939,8 @@ A typical output is:: flags: 0100002 mnt_id: 19 ino: 63107

•    size:   0
  

•    path:   /dev/null
  

All locks associated with a file descriptor are shown in its fdinfo too:: @@ -1953,6 +1958,8 @@ Eventfd files flags: 04002 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:[eventfd]
  

  eventfd-count: 5a

where 'eventfd-count' is hex value of a counter. @@ -1966,6 +1973,8 @@ Signalfd files flags: 04002 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:[signalfd]
  

  sigmask: 0000000000000200

where 'sigmask' is hex value of the signal mask associated @@ -1980,6 +1989,8 @@ Epoll files flags: 02 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:[eventpoll]
  

  tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7

where 'tfd' is a target file descriptor number in decimal form, @@ -1998,6 +2009,8 @@ For inotify files the format is the following:: flags: 02000000 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:inotify
  

  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 @@ -2021,6 +2034,8 @@ For fanotify files the format is:: flags: 02 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:[fanotify]
  

  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

@@ -2046,6 +2061,8 @@ Timerfd files flags: 02 mnt_id: 9 ino: 63107

•    size:   0
  

•    path:   anon_inode:[timerfd]
  

  clockid: 0 ticks: 0 settime flags: 01

@@ -2070,6 +2087,7 @@ DMA Buffer files mnt_id: 9 ino: 63107 size: 32768

•    path:   /dmabuf:
  

  count: 2 exp_name: system-heap

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index b1e25ae98302..d61183ff3c30 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -377,7 +377,6 @@ 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 913bef0d2a36..a8a968bc58f0 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -54,10 +54,15 @@ 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",

• seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\nino:\t%lu\nsize:\t%zu\n", (long long)file->f_pos, f_flags, real_mount(file->f_path.mnt)->mnt_id,

•    file_inode(file)->i_ino);
  

•    file_inode(file)->i_ino,
  

•    file_inode(file)->i_size);
  

We might consider splitting this into multiple seq_printf calls, one for each printed attribute.

It becomes a bit unreadable and the minimal additional overhead shouldn't matter that much.

Regards, Christian.

• seq_puts(m, "path:\t");
• seq_file_path(m, file, "\n");
• seq_putc(m, '\n');

/* show_fd_locks() never deferences files so a stale value is safe */ show_fd_locks(m, file, files);

base-commit: b015dcd62b86d298829990f8261d5d154b8d7af5