Unverified Commit b4dba2ef authored by Christian Brauner's avatar Christian Brauner
Browse files

proc: store cookie in private data 

Store the cookie to detect concurrent seeks on directories in
file->private_data.

Link: https://lore.kernel.org/r/20240830-vfs-file-f_version-v1-14-6d3e4816aa7b@kernel.org


Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent ceaa5e80

fs/proc/base.c

+24 −6
Original line number Diff line number Diff line
@@ -3870,12 +3870,12 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx) 
	if (!dir_emit_dots(file, ctx))

		return 0;



	/* f_version caches the tgid value that the last readdir call couldn't

	 * return. lseek aka telldir automagically resets f_version to 0.

	/* We cache the tgid value that the last readdir call couldn't

	 * return and lseek resets it to 0.

	 */

	ns = proc_pid_ns(inode->i_sb);

	tid = (int)file->f_version;

	file->f_version = 0;

	tid = (int)(intptr_t)file->private_data;

	file->private_data = NULL;

	for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);

	     task;

	     task = next_tid(task), ctx->pos++) {
@@ -3890,7 +3890,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx) 
				proc_task_instantiate, task, NULL)) {

			/* returning this tgid failed, save it as the first

			 * pid for the next readir call */

			file->f_version = (u64)tid;

			file->private_data = (void *)(intptr_t)tid;

			put_task_struct(task);

			break;

		}
@@ -3915,6 +3915,24 @@ static int proc_task_getattr(struct mnt_idmap *idmap, 
	return 0;

}



/*

 * proc_task_readdir() set @file->private_data to a positive integer

 * value, so casting that to u64 is safe. generic_llseek_cookie() will

 * set @cookie to 0, so casting to an int is safe. The WARN_ON_ONCE() is

 * here to catch any unexpected change in behavior either in

 * proc_task_readdir() or generic_llseek_cookie().

 */

static loff_t proc_dir_llseek(struct file *file, loff_t offset, int whence)

{

	u64 cookie = (u64)(intptr_t)file->private_data;

	loff_t off;



	off = generic_llseek_cookie(file, offset, whence, &cookie);

	WARN_ON_ONCE(cookie > INT_MAX);

	file->private_data = (void *)(intptr_t)cookie; /* serialized by f_pos_lock */

	return off;

}



static const struct inode_operations proc_task_inode_operations = {

	.lookup		= proc_task_lookup,

	.getattr	= proc_task_getattr,
@@ -3925,7 +3943,7 @@ static const struct inode_operations proc_task_inode_operations = { 
static const struct file_operations proc_task_operations = {

	.read		= generic_read_dir,

	.iterate_shared	= proc_task_readdir,

	.llseek		= generic_file_llseek,

	.llseek		= proc_dir_llseek,

};



void __init set_proc_pid_nlink(void)