From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8F0541A934 for ; Fri, 17 Jul 2026 14:00:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784296823; cv=none; b=iB7gAKHTJ4tKqSP/BysTQb9LenCqvYZs/srQDghRd/e+kD58Mupx+VQVIqx3jA2WmDncuNTKK1sNp5hV+xeiZc8YYxWTw3OKdJpMXVlvNpnlfA2MdLejSZHmp7HAFtGjQSAgUpgn8rtFnVyUeg8oDNf2rECMA5I+P+gORugKZts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784296823; c=relaxed/simple; bh=CFaMpbdKkzHtQzOUy1lMMgQ5Ifs+FH7ktYX8uXSXJ2g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=q7V5mXEmozKkVG8LDDiDddv3U0pr57/dB5qdDIPAxZBOrhNK/DvR05EQyKHOwIPcuERW33WoBcZJvz2fliZtKAFjExPCXI271VovHpze0yQvs3OmzOhe7flw8yMiqmkaNZ2DI39AtmY+o8lHcrpdKoDvz5yGK5Nnchni88OHVxI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A00UT84f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A00UT84f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5E221F00A3D; Fri, 17 Jul 2026 14:00:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784296821; bh=PTCWqRVUX5LWtcu4jvnB2rnSvbblijjCnEN7z/WG85k=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=A00UT84f/3rSg5OGNYef0vC0pCqwDxbKQGlGINiMdahSivS1tWu0s63azH/YjYjME trEzG72mLbjuJnz3HULlRHVLRQu5UZHnKrfqTvA53tLvIvxaOKlgwG7+Mq7sKGBLLw vO+6guE27Gzon+VG0E6xAjaYbrtY8gdMGkgDsp3030gP7oblorjp5kPUVg0HmpRHkg 1fagnfISvNsjJJVjfSknuTHyG1R29+ZhwSnPxmsK9qBBzthz04XVhnJpL0V6uAtb9b YEMH43NAP+lBTMFZxysgoVERX64DlfErPWc9C+MQGJqLkjnWuqR/VB90az04DboQ4E 2FwctmPJKVqCQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Jann Horn , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 5.15.y 4/4] proc: protect ptrace_may_access() with exec_update_lock (FD links) Date: Fri, 17 Jul 2026 10:00:16 -0400 Message-ID: <20260717140016.1717138-4-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260717140016.1717138-1-sashal@kernel.org> References: <2026071447-twitter-wick-5966@gregkh> <20260717140016.1717138-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jann Horn [ Upstream commit 6255da28d4bb5349fe18e84cb043ccd394eba75d ] proc_pid_get_link() and proc_pid_readlink() currently look up the task from the pid once, then do the ptrace access check on that task, then look up the task from the pid a second time to do the actual access. That's racy in several ways. To fix it, pass the task to the ->proc_get_link() handler, and instead of proc_fd_access_allowed(), introduce a new helper call_proc_get_link() that looks up and locks the task, does the access check, and calls ->proc_get_link(). Fixes: 778c1144771f ("[PATCH] proc: Use sane permission checks on the /proc//fd/ symlinks") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Link: https://patch.msgid.link/20260518-procfs-lockfix-part1-v1-2-5c3d20e0ac33@google.com Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- fs/proc/base.c | 119 ++++++++++++++++++--------------------------- fs/proc/fd.c | 27 +++++----- fs/proc/internal.h | 2 +- 3 files changed, 59 insertions(+), 89 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 93b0b5e89d0803..bb68202c369b90 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -218,33 +218,24 @@ static int get_task_root(struct task_struct *task, struct path *root) return result; } -static int proc_cwd_link(struct dentry *dentry, struct path *path) +static int proc_cwd_link(struct dentry *dentry, struct path *path, + struct task_struct *task) { - struct task_struct *task = get_proc_task(d_inode(dentry)); int result = -ENOENT; - if (task) { - task_lock(task); - if (task->fs) { - get_fs_pwd(task->fs, path); - result = 0; - } - task_unlock(task); - put_task_struct(task); + task_lock(task); + if (task->fs) { + get_fs_pwd(task->fs, path); + result = 0; } + task_unlock(task); return result; } -static int proc_root_link(struct dentry *dentry, struct path *path) +static int proc_root_link(struct dentry *dentry, struct path *path, + struct task_struct *task) { - struct task_struct *task = get_proc_task(d_inode(dentry)); - int result = -ENOENT; - - if (task) { - result = get_task_root(task, path); - put_task_struct(task); - } - return result; + return get_task_root(task, path); } /* @@ -704,23 +695,6 @@ static int proc_pid_syscall(struct seq_file *m, struct pid_namespace *ns, /* Here the fs part begins */ /************************************************************************/ -/* permission checks */ -static int proc_fd_access_allowed(struct inode *inode) -{ - struct task_struct *task; - int allowed = 0; - /* Allow access to a task's file descriptors if it is us or we - * may use ptrace attach to the process and find out that - * information. - */ - task = get_proc_task(inode); - if (task) { - allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS); - put_task_struct(task); - } - return allowed; -} - int proc_nochmod_setattr(struct user_namespace *mnt_userns, struct dentry *dentry, struct iattr *attr) { @@ -1779,16 +1753,12 @@ static const struct file_operations proc_pid_set_comm_operations = { .release = single_release, }; -static int proc_exe_link(struct dentry *dentry, struct path *exe_path) +static int proc_exe_link(struct dentry *dentry, struct path *exe_path, + struct task_struct *task) { - struct task_struct *task; struct file *exe_file; - task = get_proc_task(d_inode(dentry)); - if (!task) - return -ENOENT; exe_file = get_task_exe_file(task); - put_task_struct(task); if (exe_file) { *exe_path = exe_file->f_path; path_get(&exe_file->f_path); @@ -1798,26 +1768,42 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path) return -ENOENT; } +static int call_proc_get_link(struct dentry *dentry, struct inode *inode, struct path *path_out) +{ + struct task_struct *task; + int ret; + + task = get_proc_task(inode); + if (!task) + return -ENOENT; + ret = down_read_killable(&task->signal->exec_update_lock); + if (ret) + goto out_put_task; + if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) { + ret = -EACCES; + goto out; + } + ret = PROC_I(inode)->op.proc_get_link(dentry, path_out, task); + +out: + up_read(&task->signal->exec_update_lock); +out_put_task: + put_task_struct(task); + return ret; +} + static const char *proc_pid_get_link(struct dentry *dentry, struct inode *inode, struct delayed_call *done) { struct path path; - int error = -EACCES; + int error; if (!dentry) return ERR_PTR(-ECHILD); - - /* Are we allowed to snoop on the tasks file descriptors? */ - if (!proc_fd_access_allowed(inode)) - goto out; - - error = PROC_I(inode)->op.proc_get_link(dentry, &path); - if (error) - goto out; - - error = nd_jump_link(&path); -out: + error = call_proc_get_link(dentry, inode, &path); + if (!error) + error = nd_jump_link(&path); return ERR_PTR(error); } @@ -1851,17 +1837,11 @@ static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int b struct inode *inode = d_inode(dentry); struct path path; - /* Are we allowed to snoop on the tasks file descriptors? */ - if (!proc_fd_access_allowed(inode)) - goto out; - - error = PROC_I(inode)->op.proc_get_link(dentry, &path); - if (error) - goto out; - - error = do_proc_readlink(&path, buffer, buflen); - path_put(&path); -out: + error = call_proc_get_link(dentry, inode, &path); + if (!error) { + error = do_proc_readlink(&path, buffer, buflen); + path_put(&path); + } return error; } @@ -2247,21 +2227,16 @@ static const struct dentry_operations tid_map_files_dentry_operations = { .d_delete = pid_delete_dentry, }; -static int map_files_get_link(struct dentry *dentry, struct path *path) +static int map_files_get_link(struct dentry *dentry, struct path *path, + struct task_struct *task) { unsigned long vm_start, vm_end; struct vm_area_struct *vma; - struct task_struct *task; struct mm_struct *mm; int rc; rc = -ENOENT; - task = get_proc_task(d_inode(dentry)); - if (!task) - goto out; - mm = get_task_mm(task); - put_task_struct(task); if (!mm) goto out; diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 6da3da68d5e6e4..277f778146e0f5 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -170,24 +170,19 @@ static const struct dentry_operations tid_fd_dentry_operations = { .d_delete = pid_delete_dentry, }; -static int proc_fd_link(struct dentry *dentry, struct path *path) +static int proc_fd_link(struct dentry *dentry, struct path *path, + struct task_struct *task) { - struct task_struct *task; int ret = -ENOENT; - - task = get_proc_task(d_inode(dentry)); - if (task) { - unsigned int fd = proc_fd(d_inode(dentry)); - struct file *fd_file; - - fd_file = fget_task(task, fd); - if (fd_file) { - *path = fd_file->f_path; - path_get(&fd_file->f_path); - ret = 0; - fput(fd_file); - } - put_task_struct(task); + unsigned int fd = proc_fd(d_inode(dentry)); + struct file *fd_file; + + fd_file = fget_task(task, fd); + if (fd_file) { + *path = fd_file->f_path; + path_get(&fd_file->f_path); + ret = 0; + fput(fd_file); } return ret; diff --git a/fs/proc/internal.h b/fs/proc/internal.h index 4020245a89c233..9c4a5540296fcf 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -97,7 +97,7 @@ extern struct kmem_cache *proc_dir_entry_cache; void pde_free(struct proc_dir_entry *pde); union proc_op { - int (*proc_get_link)(struct dentry *, struct path *); + int (*proc_get_link)(struct dentry *, struct path *, struct task_struct *); int (*proc_show)(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task); -- 2.53.0