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authorKalesh Singh <kaleshsingh@google.com>2021-07-01 04:54:44 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-07-01 21:06:04 +0300
commit7bc3fa0172a423afb34e6df7a3998e5f23b1a94a (patch)
tree51fae6ee93cf450e32001c6434ca06e5eb32edec
parentd238692b4b9f2c36e35af4c6e6f6da36184aeb3e (diff)
downloadlinux-7bc3fa0172a423afb34e6df7a3998e5f23b1a94a.tar.xz
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@google.com Signed-off-by: Kalesh Singh <kaleshsingh@google.com> Suggested-by: Jann Horn <jannh@google.com> Acked-by: Christian König <christian.koenig@amd.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Alexey Gladkov <gladkov.alexey@gmail.com> Cc: Andrei Vagin <avagin@gmail.com> Cc: Bernd Edlinger <bernd.edlinger@hotmail.de> Cc: Christian Brauner <christian.brauner@ubuntu.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Helge Deller <deller@gmx.de> Cc: Hridya Valsaraju <hridya@google.com> Cc: James Morris <jamorris@linux.microsoft.com> Cc: Jeff Vander Stoep <jeffv@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kees Cook <keescook@chromium.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Michel Lespinasse <walken@google.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Szabolcs Nagy <szabolcs.nagy@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/proc/base.c4
-rw-r--r--fs/proc/fd.c15
2 files changed, 16 insertions, 3 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index a0a2fc1c9da2..e5b5f7709d48 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3172,7 +3172,7 @@ 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),
@@ -3517,7 +3517,7 @@ 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 07fc4fad2602..6a80b40fd2fe 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 @@ out:
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);
}
@@ -308,7 +321,7 @@ 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);