From 679c77e4f05e01946333e5e364ec1e3f31fcd72c Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@google.com>
Date: Mon, 6 Jan 2025 14:01:09 -0800
Subject: [PATCH] proc: Allow interrupting generation of
 /proc/pid/mount{s,info}

In some cases, generating /proc/pid/mount{s,info} can take a long time.
This change allows the process to be interrupted.

Reported-by: syzbot+9e7465bc6f00665727ad@syzkaller.appspotmail.com
Signed-off-by: Andrei Vagin <avagin@google.com>
---
 pkg/sentry/fsimpl/proc/task_files.go |  6 ++----
 pkg/sentry/vfs/mount.go              | 12 ++++++++++--
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/pkg/sentry/fsimpl/proc/task_files.go b/pkg/sentry/fsimpl/proc/task_files.go
index 366d9476a..55f87f130 100644
--- a/pkg/sentry/fsimpl/proc/task_files.go
+++ b/pkg/sentry/fsimpl/proc/task_files.go
@@ -1201,8 +1201,7 @@ func (i *mountInfoData) Generate(ctx context.Context, buf *bytes.Buffer) error {
 		return nil
 	}
 	defer i.fs.SafeDecRef(ctx, rootDir)
-	i.task.Kernel().VFS().GenerateProcMountInfo(ctx, rootDir, buf)
-	return nil
+	return i.task.Kernel().VFS().GenerateProcMountInfo(ctx, rootDir, buf)
 }
 
 // mountsData is used to implement /proc/[pid]/mounts.
@@ -1233,8 +1232,7 @@ func (i *mountsData) Generate(ctx context.Context, buf *bytes.Buffer) error {
 		return nil
 	}
 	defer i.fs.SafeDecRef(ctx, rootDir)
-	i.task.Kernel().VFS().GenerateProcMounts(ctx, rootDir, buf)
-	return nil
+	return i.task.Kernel().VFS().GenerateProcMounts(ctx, rootDir, buf)
 }
 
 // +stateify savable
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index c612138cf..615368957 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -1342,7 +1342,7 @@ func (mnt *Mount) Root() *Dentry {
 // GenerateProcMounts emits the contents of /proc/[pid]/mounts for vfs to buf.
 //
 // Preconditions: taskRootDir.Ok().
-func (vfs *VirtualFilesystem) GenerateProcMounts(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) {
+func (vfs *VirtualFilesystem) GenerateProcMounts(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) error {
 	rootMnt := taskRootDir.mount
 
 	vfs.lockMounts()
@@ -1361,6 +1361,9 @@ func (vfs *VirtualFilesystem) GenerateProcMounts(ctx context.Context, taskRootDi
 	sort.Slice(mounts, func(i, j int) bool { return mounts[i].ID < mounts[j].ID })
 
 	for _, mnt := range mounts {
+		if ctx.Interrupted() {
+			return linuxerr.ErrInterrupted
+		}
 		// Get the path to this mount relative to task root.
 		mntRootVD := VirtualDentry{
 			mount:  mnt,
@@ -1404,13 +1407,14 @@ func (vfs *VirtualFilesystem) GenerateProcMounts(ctx context.Context, taskRootDi
 		// is allowed.
 		fmt.Fprintf(buf, "%s %s %s %s %d %d\n", "none", path, mnt.fs.FilesystemType().Name(), opts, 0, 0)
 	}
+	return nil
 }
 
 // GenerateProcMountInfo emits the contents of /proc/[pid]/mountinfo for vfs to
 // buf.
 //
 // Preconditions: taskRootDir.Ok().
-func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) {
+func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRootDir VirtualDentry, buf *bytes.Buffer) error {
 	rootMnt := taskRootDir.mount
 
 	vfs.lockMounts()
@@ -1431,6 +1435,9 @@ func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRoo
 
 	creds := auth.CredentialsFromContext(ctx)
 	for _, mnt := range mounts {
+		if ctx.Interrupted() {
+			return linuxerr.ErrInterrupted
+		}
 		// Get the path to this mount relative to task root.
 		mntRootVD := VirtualDentry{
 			mount:  mnt,
@@ -1530,6 +1537,7 @@ func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRoo
 		// (11) Superblock options, and final newline.
 		fmt.Fprintf(buf, "%s\n", superBlockOpts(pathFromRoot, mnt))
 	}
+	return nil
 }
 
 // manglePath replaces ' ', '\t', '\n', and '\\' with their octal equivalents.