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proc: store cookie in private data

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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: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-08-30 15:04:55 +02:00
parent ceaa5e80db
commit b4dba2efa8
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 24 additions and 6 deletions
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30
fs/proc/base.c
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@ -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)