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.
Suggested-by: Jann Horn <[email protected]>
Signed-off-by: Kalesh Singh <[email protected]>
---
Changes in v2:
- Update patch description
fs/proc/base.c | 4 ++--
fs/proc/fd.c | 15 ++++++++++++++-
2 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b3422cda2a91..a37f9de7103f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3160,7 +3160,7 @@ static const struct pid_entry tgid_base_stuff[] = {
DIR("task", S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
DIR("map_files", S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
- DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
+ DIR("fdinfo", S_IRUGO|S_IXUGO, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
DIR("net", S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
@@ -3504,7 +3504,7 @@ static const struct inode_operations proc_tid_comm_inode_operations = {
*/
static const struct pid_entry tid_base_stuff[] = {
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
- DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
+ DIR("fdinfo", S_IRUGO|S_IXUGO, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
DIR("net", S_IRUGO|S_IXUGO, proc_net_inode_operations, proc_net_operations),
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index cb51763ed554..585e213301f9 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -6,6 +6,7 @@
#include <linux/fdtable.h>
#include <linux/namei.h>
#include <linux/pid.h>
+#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/file.h>
#include <linux/seq_file.h>
@@ -72,6 +73,18 @@ static int seq_show(struct seq_file *m, void *v)
static int seq_fdinfo_open(struct inode *inode, struct file *file)
{
+ bool allowed = false;
+ struct task_struct *task = get_proc_task(inode);
+
+ if (!task)
+ return -ESRCH;
+
+ allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
+ put_task_struct(task);
+
+ if (!allowed)
+ return -EACCES;
+
return single_open(file, seq_show, inode);
}
@@ -307,7 +320,7 @@ static struct dentry *proc_fdinfo_instantiate(struct dentry *dentry,
struct proc_inode *ei;
struct inode *inode;
- inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUSR);
+ inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUGO);
if (!inode)
return ERR_PTR(-ENOENT);
--
2.30.0.478.g8a0d178c01-goog
And 'inode_no' field to /proc/<pid>/fdinfo/<FD> and
/proc/<pid>/task/<tid>/fdinfo/<FD>.
The inode numbers can be used to uniquely identify DMA buffers
in user space and avoids a dependency on /proc/<pid>/fd/* when
accounting per-process DMA buffer sizes.
Signed-off-by: Kalesh Singh <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
---
Changes in v5:
- Fixed tab vs spaces, per Randy
- Renamed inode_no to ino, per Matthew
Changes in v4:
- Add inode number as common field in fdinfo, per Christian
Changes in v3:
- Add documentation in proc.rst, per Randy
Changes in v2:
- Update patch description
Documentation/filesystems/proc.rst | 37 +++++++++++++++++++++++++-----
fs/proc/fd.c | 5 ++--
2 files changed, 34 insertions(+), 8 deletions(-)
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2fa69f710e2a..7730d1c120e8 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1902,18 +1902,20 @@ 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 three fields -- 'pos', 'flags' and 'mnt_id'. 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].
+files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
+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.
A typical output is::
pos: 0
flags: 0100002
mnt_id: 19
+ ino: 63107
All locks associated with a file descriptor are shown in its fdinfo too::
@@ -1930,6 +1932,7 @@ Eventfd files
pos: 0
flags: 04002
mnt_id: 9
+ ino: 63107
eventfd-count: 5a
where 'eventfd-count' is hex value of a counter.
@@ -1942,6 +1945,7 @@ Signalfd files
pos: 0
flags: 04002
mnt_id: 9
+ ino: 63107
sigmask: 0000000000000200
where 'sigmask' is hex value of the signal mask associated
@@ -1955,6 +1959,7 @@ Epoll files
pos: 0
flags: 02
mnt_id: 9
+ ino: 63107
tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7
where 'tfd' is a target file descriptor number in decimal form,
@@ -1971,6 +1976,8 @@ For inotify files the format is the following::
pos: 0
flags: 02000000
+ mnt_id: 9
+ ino: 63107
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
@@ -1993,6 +2000,7 @@ For fanotify files the format is::
pos: 0
flags: 02
mnt_id: 9
+ ino: 63107
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
@@ -2017,6 +2025,7 @@ Timerfd files
pos: 0
flags: 02
mnt_id: 9
+ ino: 63107
clockid: 0
ticks: 0
settime flags: 01
@@ -2031,6 +2040,22 @@ details]. 'it_value' is remaining time until the timer expiration.
with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
still exhibits timer's remaining time.
+DMA Buffer files
+~~~~~~~~~~~~~~~~
+
+::
+
+ pos: 0
+ flags: 04002
+ mnt_id: 9
+ ino: 63107
+ size: 32768
+ count: 2
+ exp_name: system-heap
+
+where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
+the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
+
3.9 /proc/<pid>/map_files - Information about memory mapped files
---------------------------------------------------------------------
This directory contains symbolic links which represent memory mapped files
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 585e213301f9..2c25909bf9d1 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -54,9 +54,10 @@ 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\n",
+ seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\ninode_no:\t%lu\n",
(long long)file->f_pos, f_flags,
- real_mount(file->f_path.mnt)->mnt_id);
+ real_mount(file->f_path.mnt)->mnt_id,
+ file_inode(file)->i_ino);
/* show_fd_locks() never deferences files so a stale value is safe */
show_fd_locks(m, file, files);
--
2.30.0.478.g8a0d178c01-goog
On Mon, Feb 08, 2021 at 03:14:28PM +0000, Kalesh Singh wrote:
> - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
> + seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\ninode_no:\t%lu\n",
You changed it everywhere but here ...
On Mon, Feb 8, 2021 at 10:22 AM Matthew Wilcox <[email protected]> wrote:
>
> On Mon, Feb 08, 2021 at 03:14:28PM +0000, Kalesh Singh wrote:
> > - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
> > + seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\ninode_no:\t%lu\n",
>
> You changed it everywhere but here ...
Ahh sorry I missed this. Will resend with this corrected. Thanks Matthew.
>
On Mon, Feb 08, 2021 at 03:22:44PM +0000, Matthew Wilcox wrote:
> On Mon, Feb 08, 2021 at 03:14:28PM +0000, Kalesh Singh wrote:
> > - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
> > + seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\ninode_no:\t%lu\n",
>
> You changed it everywhere but here ...
call it "st_ino", because that's how fstat calls it?
On Mon, Feb 08, 2021 at 08:17:34PM +0300, Alexey Dobriyan wrote:
> On Mon, Feb 08, 2021 at 03:22:44PM +0000, Matthew Wilcox wrote:
> > On Mon, Feb 08, 2021 at 03:14:28PM +0000, Kalesh Singh wrote:
> > > - seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
> > > + seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\ninode_no:\t%lu\n",
> >
> > You changed it everywhere but here ...
>
> call it "st_ino", because that's how fstat calls it?
it's called "st_ino" because it's part of the stat structure.
here, it is not part of the stat structure.